MCAT chemistry exam

*If you can't balance an equation,it may be a redox reaction, where you need to "add" an acid or base to the reaction to help balance it.* percent yield

(actual yield)/(theoretical yield) x 100 = percent yield

titration of weak acid and strong base half equivalence point

*Before the titration of a weak acid with a strong base begins, the solution is 100% HA. At the half equivalence point the base has stripped the protons off of exactly half of the molecules of acid present, so at the half equivalence point [HA] =[A1- A t the equivalence point the base has stripped all of the protons from all of the acid molecules, so the solution is 100% A .* half equivalence point: *more likely on the MCAT than the equivalence point*. point where exactly one half of the acid has been neutralized by the base. In other words, the concentration of the acid is equal to the concentration of its conjugate base. Notice that the half equivalence point occurs at the midpoint of the section of the graph that most represents a horizontal line. This is the spot where the largest amount of base or acid could be added with the least amount of change in pH. Such a solution is considered to be buffered. The half equivalence point shows the point in the titration where the solution is the most well buffered.

law of mass action

*Don't use solids or pure liquids such as water in the Law of Mass Action, since their concentrations do not change over the course of the reaction. Their amounts may change, but their concentrations do not.*

henderson-hasselbalch equation

*Finding the pH at the equivalence point is a good exercise, even though you probably won't have to do it on the MCA"f®. Here are the steps: Use Ka and Kw to find the Kb Kb=Kw/Ka Set up the Kb equilibrium expression Kb=[OH-][HA]/[A-] Solve for the OH- concentration, and find the pOH. Subtract the pOH from 14 to find the pH 14-pOH=pH* *Warning! The Henderson-Hasselbalch equation cannot typically be used to find the pH at the equivalence point. Instead, the pKb of the conjugate base must be used. The Kb can be found from the pK. and the Kw-The concentration of the conjugate base at the equivalence point is equal to the number of moles of acid divided by the volume of acid plus the volume of base used to titrate. Do not forget to consider the volume of base used to titrate. Unless the base has no volume, the concentration of the conjugate at the equivalence point will not be equal to the original concentration of the acid. Finding the pH at the equivalence point involves much more calculation than finding the pH at the half equivalence point. For this reason, it is more likely that the MCAT® will ask about the pH at the half equivalence point.* *the Henderson-Hasselbalch equation is simply a form of the equilibrium expression for Ka.*

reaction quotient

*K, the equilibrium constant, gives you the standard thermodynamic favorability of a reaction in its stable, equilibrium state. K is fixed for that reaction at a certain temperature. Q, the reaction quotient, gives you a snapshot of the reaction at a point in time. When compared to K, Q tells you the direction in which the reaction must shift to reach equilibrium.*

physical reaction chemical reaction

*Know the difference between physical and chemical reactions.* physical reaction: f a compound undergoes a reaction and maintains its molecular structure (and thus its identity), the reaction is called a physical reaction. Melting, evaporation, dissolution, and rotation of polarized light are some examples of physical reactions. chemical reaction: When a compound undergoes a reaction and changes its bonding or structure to form a new compound, the reaction is called a chemical reaction. Combustion, metathesis, and redox are examples of chemical reactions.

deltaG = deltaGo + RT ln(Q)

*Memorizing this equation isn't nearly as important as understand- ing what it says about the relation- ships between deltaG, delta Go, Q, and K.* *deltaGo is a specific value of deltaG, calculated when all species have starting concentrations of one molar. Under these conditions, Q =1 and RTln{Q) =0, leaving us with deltaG= deltaGo. This is what we would expect for a reaction at standard conditions.Remember, standard conditions don't indicate a particular temperature. You can have standard conditions at any temperature, but standard conditions are usually assumed to be 298K. Note that ln{1) =0.

Arrhenius equation

*Note the effect of the activation energy (Ea) on the rate constant. Remember that negative exponents are equivalent to an exponent in the denominator. As Ea increases, the rate constant decreases.* *Does the rate of a reaction increase with temperature? Yes! Remember, kinetics and thermodynamics are separate, so increasing the rate does not tell you anything about the equilibrium. It just means that equilibrium is achieved more quickly.*

henry's law

*The most important thing to remember about Henry's law is that it demonstrates that the solubility of a gas is proportional to its vapor partial pressure. We can remember this by thinking of a can of soda. When we open the can and release the pressure, the solubility of the gas decreases, causing some gas to rise out of the solution and create the familiar hiss and foam.* In an ideally dilute solution, the solvent obeys Raoult's law and the solute obeys Henry's law. *As shown by Raoult's law and Henry's law, the partial vapor pressure of a solution component is always proportional to its mole fraction. If the component predominates as the solvent, Raoult's law says that the partial vapor pressure is proportional to the pure vapor pressure. If the component represents a tiny amount of solution, Henry's law says that the vapor partial pressure is proportional to Henry's law constant.*

photoelectric effect

*The work function can be thought of as K.E. (excess) =h f (energy in)- Φ (electron out) In this equation, hf is the energy put in by a photon, and Φ is the energy required to eject the electron from the atom. The energy left over is the electron's kinetic energy.*

heat capacity *constant volume heat capacity Cv* and a *constant pressure heat capacity Cp*. *Cp>Cv If no expansion work (PV work) is done by a system as it is heated, nearly all the heat energy goes into increasing the temperature. When the system is allowed to expand at constant pressure, however, some energy leaves the system as work and the temperature increase is diminished. Thus the constant pressure heat capacity of a sub- stance is greater than its constant volume heat capacity.* *A substance with a greater heat capacity can absorb more heat with less temperature change.*

*Think about the heat capacity of a substance as the amount of energy a substance can absorb per unit of temperature change.*

zeroth law of thermodynamics first law of thermodynamics second law of thermodynamics third law of thermodynamics

*Warning: In our definition of the First Law, we have chosen the convention where work done on the system is positive. It is possible that an MCAT passage could define work done by the system as positive, in which case the formula would be (delta E)= q- w. This is because technically, change in heat and change in work (volume) have opposite sign conventions.* *The zeroth law says that temperature, the state of motion of molecules, exists and that temperature can equilibrate. Remember temperature is not heat (heat is a type of energy transfer). The zeroth law sets up the game with a playing field for the other laws - the game is always at play. Expect to see this law in ideal gas problems. The first law, which says that change in energy is the sum of heat and work, means that you can't win. In other words, you cannot get more energy out than what you put in. The second law says that you can't "break even." Temperature and pressure flow "downhill" from greater to less. This applies to fluid and heat problems. The second law also says that the net entropy or disorder of the universe is always increasing. You can't go back to the beginning of the game- the original level of order of the universe. The third law describes the hypothetical state of absolute zero. It says that you can't ever get out of the game because the game never ends.Since absolute zero, that is zero energy, can never be achieved, energy is eternal!* second law of thermodynamics: it will never happen without some outside intervention, namely work. Another way to state the Second Law is, "The entropy of an isolated system will never decrease." *The First and Second Laws are the most important ones for the MCAT. 0TH LAW: Two bodies in thermal equilibrium with the same system are in thermal equilibrium with each other. In other words, temperature exists and is a state function. 1ST LAW: The energy of an isolated system is conserved for any reaction. 2ND LAW: The entropy of an isolated system will never decrease. 3RD LAW: A perfect crystal at zero Kelvin is assigned an entropy value of zero. All other substances a t all other temperatures have a positive entropy value. (Zero Kelvin is unattainable.) SUMMARY: Think of heat and work as the only two ways to change the energy of a system. Together heat and work result in the change in internal energy of a system at rest. Think of temperature as thermal energy per mole; think of pressure as thermal energy per volume. Think of enthalpy as U+ pv, or think of change in enthalpy at constant pressure as the heat of reaction. Think of entropy as the spreading out of energy. Entropy increases with temperature, volume, and number. Think of Gibbs energy change as the negative of the maximum amount of energy available to do non-PV work, such as electrical work in a cell.* Therefore, the sum of the entropy changes of any system and its surroundings equals the entropy change of the universe, which must be equal to or greater than zero. delta S system + delta S surrounds = delta S universe >= 0 *A reaction must increase the entropy of the universe- but not necessarily the system- in order to proceed.*

phase change

*each phase of a substance has its own specific heat.* *You should know the names of the types of phase changes: solid to liquid = melting liquid to solid =freezing liquid to gas= vaporization gas to liquid =condensation solid to gas = sublimation gas to solid = deposition* -20--> 0C solid 0--> 100C liquid

beta decay

0 -1 e *All forms of beta decay are simply the breakdown or formation of a single neutron (n) within the nucleus. This creates a proton (p+) in the former and eliminates a proton in the latter. If you keep this in mind,you do not need to memorize the reactions, as they make sense accordingly. n--> p+ + e- p+ + e- --> n Using positrons (e+) instead of electrons (e-) n + e+ --> p+ p+ --> n + e+*

11. What is the empirical formula of a neutral compound containing 58.6% oxygen, 39% sulfur, 2.4% hydrogen by mass? OA) HS03- 0B) HS04- 0C) H2S03 OD) H 2S 0 4

0C) H2S03 Oxygen: (58.6 grams)/16 grams/mole)= 3.6 moles Sulfur: (39 grams)/(32 grams/mole)= 1.2 moles Hydrogen: (2.4 grams)/(1 grams/mole)= 2.4 moles Next, divide through by the lowest number of moles, which is 1.2 moles: Oxygen: 3.6 moles/1.2 moles = 3 Sulfur: 1.2 moles/1.2 moles = 1 Hydrogen: 2.4 moles/1.2 moles= 2

27. The electrons in the n bond of an alkene have: A) 33% p character and are at a lower energy level than the electron pair in the a-bond. B) 50% p character and are at a higher energy level than the electron pair in the a-bond. C) I00% p character and are at a lower energy level than the electron pair in the a-bond. D) I00% p character and are at a higher energy level than the electron pair in the a-bond. 31. How much s character is in the hybridized orbital on either nitrogen atom in diatomic nitrogen (N2)? OA) 33.3% OB) 50% OC) 66.6% OD) 100%

27. D) I00% p character and are at a higher energy level than the electron pair in the a-bond. An alkene is a compound containing one or more carbon-carbon double bonds. This double bond is said to consist of one a bond and one TI bond. According to Valence Bond Theory, the a bond is formed by the overlap of sp2 hybrid orbitals whereas the TI bond is formed by the overlap of unhybridized p orbitals. The electrons in the TI bond, therefore, have 100% p character. Thus choices A and B can be eliminated. The electrons occupying the TI bond are said to occupy a 2p orbital whereas those in the a bond are said to occupy an sp2 hybrid orbital with energy higher than that of a 2s orbital but lower than that of a 2p orbital. Therefore, the electrons in the TI bond are considered to be at a higher energy level than those in the a bond. Therefore, choice C can be eliminated and choice D is the best answer. 31. OB) 50% Diatomic nitrogen comprises two nitrogen atoms that are triple bonded to one another. Given nitrogen's five valence electrons, this is the only configuration that will allow each atoms to obtain full octet of valence electrons. In addition to retaining a lone pair of electrons, each atom participates in one a bond, which consists of two overlapping sp hybridized orbitals and two pi bonds, each of which consists of two overlapping unhybridized p orbitals. Thus the hybridized orbitals of the nitrogen atoms are sp hybridized and exhibit 50% s character and 50% p character. sp2 hybridized orbitals exhibit 33.3% s characters. Therefore, choice A can be eliminated. No hybridized orbitals exhibit 66.6% or 100% s character; only unhybridized s orbitals exhibit 100% s character. Therefore, C and D can be eliminated. Note that sp3 orbitals exhibit 25% s character.

50. Which of the following alcohols has the lowest pKa? a) 1-pentanol b) 2-pentanol c) 3-pentanol d) cyclopentanol 52. The Lucas test distinguishes between the presence of primary, secondary, and tertiary alcohols based upon reactivity with a hydrogen halide. The corresponding alkyl chlorides are insoluble in Lucas reagent and turn the solution cloudy at the same rate that they react with the reagent. The alcohols, A, B, and C, are solvated separately in Lucas reagent made of hydrochloric acid and zinc chloride. If the alcohols are primary, secondary, and tertiary respectively, what is the order of their rates of reaction from fastest to slowest? OA) A,B, C OB) B, A, C OC) C,B,A OD) B, C, A

50. a) 1-pentanol Questions asking about the acidity of alcohols can usually be answered by looking at the electron donating and withdrawing properties of a molecule. The more electron withdrawal from an alcohol, the more stable its conjugate base will be (since the negative charge on the oxygen will be "pulled" onto the rest of the molecule by the electron withdrawing groups), thus making it more acidic. Alkyl groups, which are mildly electron donating, have the opposite effect. 2-pentanol, 3-pentanol, and cyclopentanol are all secondary alcohols, so they encounter more electron donating alkyl carbons than a primary alcohol like 1-pentanol. For this reason, 1-pentanol is the most acidic, and choice A is correct. 52. OC) C,B,A The reaction of an alcohol with a hydrogen halide to form an alkyl chloride is a substitution reaction. Regardless of whether or not the mechanism is SN1 or SN2, the hydroxyl group will not leave until it has been protonated. For SNl, the formation of the cation, although rate determining, is very fast after protonation. It is faster, in fact, than S 2, which depends on the chloride ion colliding with an already protonated molecule from the correct side. Molecules with tertiary leaving groups are the fastest to react in SN1, followed by secondaries. Primary leaving groups react only through SN2. The fastest reaction will thus involve the tertiary alcohol and the slowest will involve the primary; every choice but C can be eliminated. This is a very difficult question- organic chemistry questions this difficult are relatively rare.

gabriel synthesis

??? idk if this is the best reaction

103. Ammonia bums in air to form nitrogen dioxide and water. 4NH3(g) + 702(g)--> 4N02(g) + 6H20(L) lf 8 moles of NH3 are reacted with 14 moles of 02 in a rigid container with an initial pressure of II atm, what is the partial pressure of N02 in the container when the reaction runs to completion? (Assume constant temperature.) A) 4 atm B) 6 atm C) 11 atm D) 12 atm

A) 4 atm The number of moles of gas is extra information. If the container began at 11 atm then each gas is contributing a pressure in accordance with its stoichiometric coefficient. When the reaction runs to completion, the only gas in the container is nitrogen dioxide, so the partial pressure of nitrogen dioxide is the total pressure. The volume and temperature of the container remains constant, so the pressure is in accordance with the stoichiometric coefficient of nitrogen dioxide.

30. Relative to a bonds, pi bonds exhibit which of the following characteristics? I. Higher energy II. Increased stability III. Greater strength A) I only B) I and II only C) II and Ill only D) I, II, and Ill

A) I only Compared to the electrons that form a bonds, those that form n bonds inhabit higher energy orbitals. Therefore, I is correct and choice C can be eliminated. This higher energy is associated with decreased stability and lesser strength. Therefore, II and III are incorrect and choices B, C, and D can be eliminated. Note that although a pi bond is weaker than a a bond, a double bond is still stronger than a single bond as it contains both a a and pi bond, rather than just the a bond found in a single bond.

simple mercury barometer

Atmospheric pressure can be measured by an instrument called a simple mercury barometer. In a simple mercury barometer, a tube of mercury that is closed at one end is inverted and placed in an uncovered mercury bath that is open to the atmosphere, as shown in Figure 5.4. Some mercury will fall down into the bath, but the remainder will be suspended above in the tube. T he amount of mercury left in the tube is related to the atmospheric pressure pushing down on the mercury bath by the following equation: P atm = (density)gh P is in pascals

4.

Atoms and ions with electron configurations identical to those of the noble gases do not to have any unpaired electrons in their ground state. Ne, Na+, and 0 2- all have the same electron configuration, [Ne], and, therefore, no unpaired electrons in their ground state. Choices A, C and 0 can be eliminated. Calcium+, by contrast, has a ground state configuration of [Ar]4s1, and has one unpaired electron in its 4s subshell. Thus choice B is the correct answer.

Bohr atom Pauli Exclusion Principle Heisenberg Uncertainty Principle Aufbau principle Hund's rule

Bohr atom: which represents the atom as a nucleus surrounded by electrons in discrete electron shells Pauli Exclusion Principle: no two electrons in the same atom can have the same four quantum numbers Heisenberg Uncertainty Principle: there is an inherent uncertainty in the product of the position of a particle and its momentum. Aufbau principle: hat with each new proton added to create a new element, the new electron that is added to maintain neutrality will occupy the lowest energy level available. Hund's rule: electrons will not fill any orbital in the same subshell until all orbitals in that subshell contain at least one electron, and that the unpaired electrons will have parallel spins.

name ClO- ClO2- ClO3- ClO4- Cu+ Cu2+ Fe2+ Fe3+ H2SO4 H2SO3 NO2- NO3- SO3 2- SO4 2- CO3 2- HCO3- PO4 3- NH4+

ClO- hypochlorite ClO2- chlorite ClO3- chlorate ClO4- perchlorate Cu+ cuprous Cu2+ cupric Fe2+ ferrous Fe3+ ferric H2SO3 sulfurous acid H2SO4 sulfuric acid NO2- nitrite NO3- nitrate SO3 2- sulfite SO4 2- sulfate CO3 2- carbonate HCO3- bicarbonate PO4 3- phosphate NH4+ ammonium

75. Which of the following gas properties is needed to calculate the work done by an expanding gas? I. The initial and final pressures II. The initial and final volumes III. The path followed during the expansion A) I only B) II only C) I and II only D) I, II, and III

D) I, II, and III The work done by a gas is given by w = PdeltaV(constantpressure)· The final and initial volumes would be needed to calculate the change in volume. The equation stated is simplified, because a change in pressure would require calculus. Nonetheless, a change in pressure would also contribute to the work done by the gas. Work is a path function, not a state function, meaning it is dependent on the pathway. This is true in general, but don't confuse it with the concept of conservative forces in physics, which result in work that is path-independent. As a result, I, II, and III must be known to calculate the PV work, or work done by a gas, making choice D the correct answer.

standard state

Don't mix up standard state and STP. If the MCAT says 'standard state' assume a pressure of 1 bar (about 1 atm). The temperature will probably be 25 degrees C, but it doesn't have to be. Then ask yourself, "Under these conditions,is it a gas, liquid, or solid?" Your answer to this question is the reference form.

23. Which of the following graphs best represents the radioactive decay of238U? graph is exponential decay graph

During radioactive decay, the concentration of the decaying substance decreases exponentially. Therefore, choice D, which suggests that the amount of 238U increases over time, can be eliminated. To decide between the remaining answers, recall that radioactive decay is a first order reaction. Although the rates of first order reactions depend on starting concentration, their half-lives are constant and independent of starting concentration. After one half-life, one-half of the starting concentration will remain; after two half-lives, one-fourth will remain; after three half- lives, one-eighth will remain. Consider which graph reflects this trend. Choice A shows a curve with an increasingly negative slope, choice B shows a curve with a decreasingly negative slope, and choice C shows a linear curve with a constant slope. Because rate of decay (the slope of the curve) decreases with decreasing 238U concentration, choice B is the best answer.

zero order and first order reaction order

For the MCAT be concerned with the graphs for the zero order and first order rate laws. Note that the relationships shown are linear, with slopes equal to the rate constant for the given rate law. A typical MCAT question might draw your attention to the descending green line and ask you if the value of the rate constant decreases over time. Of course, it does not; the rate constant is constant! .

Fischer projections

In Fischer projections vertical lines are assumed to be oriented into the page. Horizontal lines are assumed to be oriented out of the page. Fischer projections are often used to represent carbohydrates and are an easy way to give information about the three- dimensional shape of a molecule.

Van der Waals' equation

It is important to understand how real gases deviate from ideal behavior. This deviation can be expressed quantitatively by Van der Waals' equation: where a and b are constants for specific gases. The variable b accounts for the actual volume occupied by a mole of gas. The variable a reflects the strength of intermolecular attractions. The values of a and b generally increase with the molecular mass and molecular complexity of a gas. The result is that these complex gases deviate more significantly from ideal behavior. Taking into account the volume of the molecules, *Vreal > Videal* where Videal is calculated from PV= nRT *Once again, be careful about the confusion with PV=nRT. It seems like increasing pressure also increases temperature, so how can ideal behavior deviations occur with either an increase in pressure or a decrease in temperature? The answer is that deviations in ideal behavior result from any situation in which molecules are moved closer together. In other words, gases deviate when volume is decreased. Volume can be decreased by squeezing the molecules together with high pressure, or by lowering the temperature and letting the molecules settle close together. From PV=nRf, we see that volume decreases with either increasing pressure or decreasing temperature* *Preal < Pideal* Where Pideal is calculated from PV= nRT *Remember, most gases on the MCA"f® actually can be considered to be ideal. Assume ideal behavior unless instructed otherwise.*

*phosphoric acid*

Know the general structure of phosphoric acids for the MCAT. When heated, phosphoric acids form phosphoric anhydrides. Phosphoric acids react with alcohols to form esters. phosphoric acid + heat --> phosphoric anhydride phosphoric anhydride + alcohol --> ester

Lewis acid Lewis base Arrhenius acid Arrenhius base Bronsted-Lowry acid Bronsted-Lower base

Lewis acid: accepts pair of electrons Lewis base: donates pair of electrons Arrhenius acid: produces H+ in water Arrenhius base: produces OH- in water Bronsted-Lowry acid: donates H+ Bronsted-Lower base: accepts H+ *In a series of oxyacids, acid strength increases as the number of oxygen atoms increases.* C-H, H-Cl increasing polarity --> equal bond strength <--> increasing acidity --> H-F, H-Cl, H-Br, H-I polarity increase <-- increase bond strength <-- increase acidity --> *By the way, when we say "strong acid" in inorganic chemistry, we mean an acid that is stronger than H30+ . A strong base is stronger than OW. With bases, we often call something as strong as OW, like NaOH, a strong base. For the purpose of the MCAT, assume that a strong acid or base completely dissociates in water.*

Le Chatlier *Systems "like" to be in equilibrium. When a system a t equilibrium is stressed, the system will shift in a direction to reduce that stress by reducing a substance that has been added, replacing a substance that has been taken away, and so on.*

N2 (g) + 3H2 (g) --> 2NH3 (g) + heat If the size of the container is reduced at constant temperature, total pressure increases. Since there are four gas molecules on the left side of the reaction and only two on the right, the equilibrium shifts to the right, producing heat and raising the NH3 concentration. If the temperature is raised by adding heat (analogous to adding more product), the reaction is pushed to the left. The partial pressures of N2 and H2 increase, while the concentration ofNH3 decreases.

2. Which of the following most likely represents the correct order of ion size from greatest to smallest? OA) 02-,F-,Na+,Mg2+ OB) Mg2+,Na+,F-,02- 0C) Na+,Mg2+,02-,F- OD) Mg2+,Na+,02-, F-

OA) 02-,F-,Na+,Mg2+ This is an isoelectronic series, which means that the number of electrons on each ion is the same. In an isoelectronic series of ions, the nuclear charge increases with increasing atomic number and draws the electrons inward with greater force. The ion with fewest protons produces the weakest attractive force on the electrons and thus has the largest size. Oxygen has the smallest atomic number, and thus the fewest protons. Therefore, it will have the greatest ion size.

8. Aluminum has only one oxidation state, while chromium has several. Which of the following is the best explanation for this difference? OA) Electrons in the d orbitals of Cr may or may not be used to form bonds. OB) Electrons in the p orbitals ofCr may or may not be used to form bonds. OC) Electrons in the d orbitals of AI may or may not be used to form bonds. OD) Electrons in the p orbitals of AI may or may not be used to form bonds.

OA) Electrons in the d orbitals of Cr may or may not be used to form bonds. Remember to make use of the periodic table that is provided whenever possible. Based on chromium's position in the periodic table, it can be inferred that it is a transition metal. As such, the electrons in its d orbitals have the ability to move into valence orbitals and form bonds. Depending on the number of electrons that move from the d orbitals, its oxidation state can vary considerably. Note that aluminum, like all elements in the third and higher periods, has d orbitals. However, unlike chromium, aluminum does not, in its ground state, have electrons in its d orbitals; its configuration is [Ne]3s23p1• Therefore, answer choice C can be eliminated.

120. A student has a block of an unknown solid in the laboratory. Which of the following will most likely melt the block? I. Heating the solid at constant pressure ll. Compressing the solid at constant temperature III. Accelerating the solid to high speeds to increase its kinetic energy OA) I only OB) I and Il only OC) I and lII only OD) I, II, and III

OA) I only Heating the solid will raise its temperature and will eventually melt it. Compressing the solid will raise the pressure on the solid which will most likely keep it a solid. A few substances like water will melt under pressure, but, for most substances, pressure changes a liquid to a solid. It is the random kinetic energy of the molecules of a solid and not the uniform translational motion kinetic energy of the solid that increases its temperature and cause it to melt.

64. The normal reactivity of methyl benzoate is affected by the presence of certain substituents. Which of the following substituents will decrease methyl benzoate reactivity making it safer for transport? OA) NO2 OB) Hydrogen OC) Br OD) CH3

OA) NO2 In order to decrease the reactivity of a benzene molecule, an electron withdrawing deactivating substituent must be used. Hydrogen and alkyl groups are mildly electron donating, so choices B and D are incorrect. Halides are only mildly electron withdrawing. NO:u on the other hand, is strongly electron withdrawing and should stabilize the methyl benzoate, decreasing reactivity. This will make the compound safer for transport and storage. For this reason, choice A is correct and C is incorrect.

106. Using a bomb calorimeter, the change in energy for the combustion of one mole of octane is calculated to be - 5.5 x 103 kJ. Which of the following is true concerning this process? OA) Since no work is done, the change in energy is equal to the heat. OB) Since there is no work, the change in energy is equal to the enthalpy. OC) Since work is done, the change in energy is equal to the heat. OD) The work done can be added to the change in energy to find the enthalpy.

OA) Since no work is done, the change in energy is equal to the heat. Remember, delta E = w + q. There is no work done because there is no change in volume in a bomb calorimeter. Work= PdeltaV so choice C can be ruled out as incorrect. Thus, the total change in energy is heat. Heat is not enthalpy. Heat equals enthalpy at constant pressure, and the pressure is not constant in a bomb calorimeter, therefore choice B is incorrect.

84. Sulfur dioxide reacts with oxygen in a reversible reaction to form sulfur trioxide as shown. 2S02(g) + 0 2(g)<--> 2S03(g) delta H = -200 kJ/mol If the temperature at which the reaction takes place is increased, which of the following will take place? OA) The rates of both the forward and reverse reactions will increase. OB) Only the rate of the forward reaction will increase. OC) Only the rate of the reverse reaction wiII increase. OD) The rates of neither the forward nor reverse reactions will increase.

OA) The rates of both the forward and reverse reactions will increase. Increasing the temperature increases the energy available to both the forward and the reverse reactions, enabling both to more easily overcome the activation energy. As a note, the rate of the reverse reaction will increase more than the rate of the forward reaction. This is because the reaction is exothermic, making heat a product. Based on Le Chatelier's law, an increase in temperature (heat) will cause a leftward shift by increasing the reverse rate of reaction more than the forward rate.

101. Consider two gases A and 8 with different molecular weights in fixed containers of the same volume and pressure. All of the following are true EXCEPT: OA) both gases have the same average kinetic energy. OB) the volumes of a molecule of gas A and a molecule of gas B are equal. OC) the average force exerted on the container by gas A is the same as that exerted by gas B. OD) the molecules of gas A exert no forces on each other when not colliding.

OA) both gases have the same average kinetic energy. These two containers of gas of equal mass have different molecular weights, thus there must be a different number of moles of each gas in each container. If pressure and volume are constant then by the ideal gas law (PV =nRT) the temperatures of the two gases must be different. Average Kinetic Energy for a gas is proportional to the gas's temperature. The other answers are assumed to be true for all ideal gases.

149. The addition of an electron withdrawing group to the alpha carbon of a carboxylic acid will: OA) increase the acidity of the proton by making the 0 - H bond more polar. 08) increase the acidity of the proton by making the 0-H bond stronger. OC) decrease the acidity of the proton by making the 0 - H bond more polar. OD) decrease the acidity of the proton by stabilizing the conjugate base.

OA) increase the acidity of the proton by making the 0 - H bond more polar. The electron withdrawing group will further polarize the 0-H bond, and polarization increases acidity in aqueous solution. Even if the 0-H bond became stronger, which it does not, this change would result in a weaker acid. Choice Cis the opposite of choice A Choice 0 is false, as a stabilization of the conjugate base would cause the acid to be stronger, more readily turning into the conjugate base.

58. Carboxylic acids typically undergo all of the following reactions EXCEPT: OA) nucleophilic addition. OB) nucleophilic substitution . OC) decarboxylation. OD) esterification .

OA) nucleophilic addition. This is a straightforward content question. Nucleophilic substitution is one of the most common and important reaction types for carboxylic acids, so choice B can be eliminated. As the name implies, decarboxylation involves the removal of a carboxylic acid group, making choice C incorrect. Esterification is an ester-forming reaction that occurs between carboxylic acids and alcohols, so choice D can also be eliminated. Nucleophilic addition reactions are favored by ketones and aldehydes, but do not occur with carboxylic acids.

18. Which of the following expressions is the correct rate law for the reaction? OA) rate= 0.l[A] OB) rate = [A] OC) rate = [A][B] OD) rate = [Af[B]

OA) rate= 0.l[A] Between Trials 1 and 2, the concentration of B is doubled, the concentration of A is kept constant, and the reaction rate doesn't change. Thus, we know that the reaction rate does not depend on the concentration of B. Choices C and D can be eliminated. Between Trial1 and Trial 3, the concentration of A is doubled, the concentration of B is kept constant, and the reaction rate doubles. The reaction is first order overall, and first order with respect to A. Recall that every rate law includes a rate constant. In this case, rate= k[A]. Therefore, choice B can be eliminated and choice A is the best answer. To confirm that k is, in fact, equal to 0.1, and, using the values for any trial, solve for k, which equals rate/[A].

123. A student has 0.8 liters of a 3 MHC I solution. How many liters of distilled water must she mix with the 3 M solution in order to create a 1M HCI solution? OA) 0.8 L OB) 1.6L OC) 2.4 L OD) 3.2 L

OB) 1.6L First find the number of moles of HCl. moles= (mol/L)(L) = (3 mol/L)(0.8 L) = 2.4 moles of HCl. Now find the number of liters needed to make the solution 1 molar L = (mol)/(mol/L) = (2.4 mol)/(1 M) = 2.4 L Now be careful. There are already 0.8 liters of solution, so in order to get 2.4 L, 1.6 L of water need to be added.

100. Suppose that you constructed a simple barometer using water instead of mercury. Approximately how high would the water raise in the tube at sea level? (Note: Assume Parm = 1 atm = 101,325 Pa = 760 mrnHg. The specific gravity of mercury = 13.6.) OA) 1.3 m OB) 10m OC) 13m OD) 100m

OB) 10m There are two possible approaches to this problem. First, the height of the substance in the tube can be calculated using Patm= pgh. 101,325 Pa = (1000 kg/m3) (10 m/s2)h. h ::::10 m. Also remember that 1 atm = 760 mmHg. Mercury is 13.6 times denser than water, so water will rise 13.6 times as high, or approximately 14 times higher. 760 mmHg≈ 10,640 mmH20 = 10.64 m. The closest answer is choice B, 10m.

150. Suppose that a student prepares two acidic solutions. Solution A has a hydrogen ion concentration of 6.0 X I0^-5 M. Solution B has a hydrogen ion concentration of l X I0^-7 M. The pH of solution A differs from that of solution B by: OA) 1.3. OB) 2.8. OC) 3.7. OD) 5.0.

OB) 2.8. The pH of solution B is 7. The pH of solution A is between 4 and 5. This is because the a hydrogen ion concentration of 1.0 x 10·5 mole V would result in a pH of 5, and a 1.0 x 10·6 mole L·' would result in a pH of 5. Additionally, if the hydrogen ion concentration is greater than a known value, then the value for the pH will be smaller, and vice versa. The only pH difference between 7 and 4 to 5 is choice B, 2.8.

38. Which of the following functional groups are found in phenylalanine? OA) Alkyl, double bond, and aromatic ring OB) Amine, carboxylic acid, and aromatic ring OC) Double bond, amide, and alcohol OD) Aromatic ring, halide, and ketone

OB) Amine, carboxylic acid, and aromatic ring The NH3 group is indicative of amines, and they do indeed act as weak bases.

138. Which of the following is true for a reaction, if delta Go=0? OA) The reaction is at equilibrium. OB) At 298 K and 1 M concentrations of products and reactants, the equilibrium constant equals one. OC) is also zero. OD) The reaction is spontaneous at temperatures greater than 298 K.

OB) At 298 K and 1 M concentrations of products and reactants, the equilibrium constant equals one. This question requires knowledge of the equation: delta Go=-RT ln(K). This equation is a statement about the relationship between and K at a specific temperature. If 0, then K = 1. The standard state for an aqueous solution is 1M concentrations. Don't confuse with At equilibrium = 0 and is given as in the equation given above. Thus, choices A and C state the same incorrect assumption.

32. Which of the following is NOT true? OA) Bond strength is negatively correlated with bond length. OB) Bond length is positively correlated with bond dissociation energy. OC) Bond energy is positively correlated with bond strength. OD) Bond dissociation energy is positively correlated with bond strength.

OB) Bond length is positively correlated with bond dissociation energy. Bond length is negatively correlated with bond dissociation energy. Therefore, choice B, which states that bond length is positively correlated with bond dissociation energy is NOT true. Recall that bond dissociation energy is a measure of bond strength. Because the breaking of a bond is an endothermic process, bond dissociation energy is always positive. Shorter, stronger bonds have more positive bond dissociation energies than longer, weaker bonds. Because shorter bonds are stronger bonds, choice A, which states that bond strength is negatively correlated with bond length, is a true statement and can be eliminated. Similarly, choice D, which states that bond dissociation energy is positively correlated with bond strength, is true and can, likewise, be eliminated. Recall that bond energy, like bond dissociation energy, is also a measure of bond strength. Shorter, stronger bonds also have more positive bond energies than longer, weaker bonds. Therefore, choice C, which states that bond energy is positively correlated with bond strength is a true statement and can be eliminated.

3. Which of the following species has an unpaired electron in its ground-state electronic configuration? OA) Ne OB) Ca+ OC) Na+ OD) 0 2-

OB) Ca+ Only elements in the third and higher periods of the periodic table, such as sulfur, can form more than four bonds. Second period elements, including oxygen, have four valence orbitals-one 2s and three 2p-with which to form bonds. By contrast, third period elements like sulfur can form bonds with not only one 3s and three 3p, but also five 3d valence orbitals. Remember, the second quantum number, that is, the number of available subshells, can have any integer value from 0 ton -1. When n = 3, three subshells- s, p, and d-are available. Note that this does not mean all are occupied while the atom is in its ground state configuration. The ground state configuration of sulfur, for example, is [Ne]3s^23p^4•

14. When gaseous ammonia is passed over solid copper(Il) oxide at high temperatures, nitrogen gas is formed. 2NH3(g) + 3CuO(s)---> N2(g) + 3Cu(s) + 3H20(g) What is the limiting reagent when 34 grams of ammonia form 26 grams of nitrogen in a reaction that runs to completion? OA) NH3 OB) CuO OC) N2 OD) Cu

OB) CuO The molar mass of ammonia is 17 g. Therefore, 34 g of ammonia is equal to 2 moles of ammonia. According to the balanced chemical equation, ammonia and nitrogen and consumed and produced, respectively, in a 2 to 1 ratio. Therefore, if ammonia were the limiting reagent, 28 g of nitrogen would be produced; the molar mass of molecular nitrogen is 28 g. Because only 26 g were produced, some other reagent must be limiting the yield. The only other reactant is CuO. Therefore, choice B is the correct answer.

126. A solution composed of ethanol and methanol can be thought of as ideal. At room temperature, the vapor pressure of ethanol is 45 mmHg and the vapor pressure of methanol is 95 mmHg. Which of the following will be true regarding the vapor pressure of a solution containing only ethanol and methanol? OA) It will be less than 45mmHg. OB) It will be greater than 45 mmHg and less than 95mmHg. OC) It will be greater than 95 mmHg and less than 140mmHg. OD) It will be greater than 140 mmHg.

OB) It will be greater than 45 mmHg and less than 95mmHg. In an ideal solution, the vapor pressure will be somewhere in between the vapor pressures of the solute and the solvent, depending on their relative mole fractions.

5. What is the electron configuration of chromium? OA) [Ar]3d6 OB) [Ar] 4s1 3d5 OC) [Ar]4s2 3d3 OD) [Ar]4s2 4p4

OB) [Ar] 4s1 3d5 The electron configurations of Cr and Cu are two commonly cited examples of unpredictable configurations. Both Cr and Cu have only one electron in the 4s orbital. Therefore, choice B must be the correct answer. Cr is [Ar] 4s^1 3d^5 Cr and Cu is special case However, even without any pre-existing knowledge of the electron configuration of chromium, the correct answer might have been identified by eliminating improbable choices. Choice C could have been eliminated because it contains the wrong number of electrons. Choice 0 could be eliminated because chromium ground state electrons exist in the 3d rather than the 4d subshell. Only choices A and B would have remained. Given Hund's rule, which states that the most stable arrangement of electrons is the one with the most unpaired electrons, all with the same spin, choice B might have seemed more likely to be correct. Note that Hund's rule really only applies to degenerate orbitals; it just so happens that the 4s and 3d orbitals of Cr and Cu are, in fact, at the same energy level.

35. Benzene exhibits resonance. The carbon-carbon bonds of benzene are: OA) shorter and stronger than the double bond of an alkene. OB) longer and weaker than the double bond of an alkene. OC) longer and stronger than the carbon-carbon bond of an alkane. OD) longer and weaker than the carbon-carbon bond of an alkane.

OB) longer and weaker than the double bond of an alkene. Bonds that are stronger are shorter, eliminating choice C. The bonds are stabilized by resonance and are shorter and stronger than carbon-carbon alkane bonds but longer and weaker than carbon-carbon alkene bonds, eliminating choices A and D.

98. If the density of a gas is given asp which of the following expressions represents the molecular weight of the gas? OA) Pp/RT OB) pRT/P OC) nRT/Pp OD) Pp/RT

OB) pRT/P This is essentially an algebra question that tests your understanding of density and the ideal gas law. Remember that density (p) is mass (m) divided by volume (V) and the ideal gas law is PV = nRT. Mass (m) is molecular weight (MW) times moles (n). Substituting in for mass in the density equation gives us p = m/V = (nMW)/V. After some algebra we have: MW = (pV)/n. From the ideal gas law we know that V/n = RT/P. Substituting RT/P for V/n gives MW = pRT/P, which is choice B.

115. When heat energy is added evenly throughout a block of ice at 0°C and I atm, all of the following are true EXCEPT: OA) the temperature remains constant until all the ice is melted . OB) the added energy increases the kinetic energy of the molecules. OC) entropy increases. OD) hydrogen bonds are broken.

OB) the added energy increases the kinetic energy of the molecules. Watch out for the 'EXCEPT' in this question. The added energy goes into breaking bonds not increasing the kinetic energy of the molecules, so choice B is not true. As is demonstrated by the heat curve the temperature remains constant until all the ice is melted so choice A is true. Entropy increases moving to the right on the heat curve and as an organized solid transitions to a more fluid flowing liquid. Intramolecular hydrogen bonds are broken as the ice transitions to water.

82. The standard enthalpy of formation for liquid water is: H2(g) + 1/20 2(g) -> H20(L) Delta Hf = - 285.8 kJ/mol Which of the following could be the standard enthalpy of formation for water vapor? OA) -480.7 kJ/mol OB) - 285.8 kJ/mol OC) - 241.8 kJ/mol OD) +224.6 kJ/mol

OC) - 241.8 kJ/mol The standard enthalpy of formation for water vapor is H2(g) + Yz02(g) H20(g). The product in the reaction given in the question is H20(Z). The formation of a gas requires more heat than the formation of a liquid, therefore 6.H must be greater than -285.9 kJ/mol, eliminating choices A and B. -285.9 kJ/mol represents the energy released from the formation of covalent bonds, which are intramolecular forces. The difference between liquid water and water vapor is a phase change, which is achieved by breaking intermolecular forces. Intermolecular forces are weaker than intramolecular forces, therefore the amount of additional energy added to -285.9 kJ/mol would not exceed 285.9 kJ/mol, eliminating choice D. The phase change is actually achieved with 44 kJ/mol, making the exact answer -241.8 kJ/mol. Elimination of the other answer choices would leave only this answer.

166. A buffered solution has a pH that cannot readily be changed. A buffered solution will be produced by mixing equal volumes of: OA) 1M HCI and IM NaC2H302. OB) 1 MHCI and I MNaOH. OC) 1 M HC2H302 and I M NaC2H302 OD) 1M HC2H302 and IM NaOH.

OC) 1 M HC2H302 and I M NaC2H302 A buffered solution is formed when equal amounts of a weak acid and its conjugate base are present in a solution. Acetic acid is a weak acid and the acetate ion is its conjugate. The rest of the options contain strong acids or bases, and non-conjugate pairs.

155. Carbonic acid has a Ka of 4.3 X I0^-7. What is the pH when 1 mole of NaHC03 is dissolved in 1 liter of water? OA) 3.2 OB) 3.8 OC) 10.2 OD) 12.5

OC) 10.2 The Kb for NaHC03 is Kw/Ka = Kb= 0.25 x 10-7. We can set up the equilibrium expression: Kb=[OH-][H2CO3]/[HCO3-] 0.25 x 10^-7 = [x][x]/[1-x] (bottom x is insignificant) 0.25 X 10^-8 = x^2 1.5 x 10^-4=x Thus, the pOH =between 3 and 4. Subtracting from 14, the pH is between 10 and 11.

28. Which bond angle is associated with the greatest covalent bond strength? OA) 109° OB) 120° OC) 180° OD) 360°

OC) 180° Triple bonds are stronger than either double or single bonds. Therefore, it makes sense to begin by looking for the bond angle associated with triple bonds. Recall that triple bonds consist of one a bond formed by the overlap of two sp hybridized orbitals and two TI bonds, each formed by the overlap of two unhybridized p orbitals. sp hybridization is associated with a linear geometry and, therefore, bond angles of 180°. Thus Cis the best answer choice. Double bonds consist of one a bond formed by the overlap of two sp2 hybridized orbitals and one TI bond formed by the overlap of two unhybridized p orbitals. sp2 hybridization is associated with trigonal planar geometry, and therefore, bond angles of approximately 120°. Thus choice B can be eliminated. Single bonds consist of one a bond formed by the overlap of two sp3 hybridized orbitals. sp3 hybridization is associated with a tetrahedral geometry, and, therefore, bond angles of approximately 109.5°. Thus choice A can be eliminated. Note that bond angles can vary depending on the presence of lone pair electrons. No bond has an angle of 360°. Therefore choice D can also be eliminated.

165. Which of the following is the equivalence point when the weak acid acetic acid is titrated with NaOH? OA) 4.3 OB) 7 OC) 8.7 OD) 14

OC) 8.7 The equivalence point of a titration of a weak acid with a strong base will always be greater than 7. This is the same as adding the conjugate base of the acid to pure water. 14 is way too basic. Pure 1M NaOH has a pH of 14. pH 7 is the equivalence point for strong-strong titration.

39. Which of the following functional groups is most likely to act as an electron donor in a reaction? OA) Sulfonic acid OB) Nitro group OC) Amino group OD) Quaternary ammonium group

OC) Amino group The amino group is the only possible electron donor of the choices provided: amino groups can donate electrons from their lone pair. Sulfonic acids, nitro groups, and quaternary ammonium groups are all electron withdrawing and can be eliminated.

68. Which of the following nutrients has the greatest heat of combustion? OA) Carbohydrate OB) Protein OC) Saturated fat OD) Unsaturated fat

OC) Saturated fat Asking about heat of combustion is another way of asking about the energy storage potential of these molecules. Fats have the greatest energy storage potential, much more, about twice as much, than that of carbohydrates and proteins, so choices A and B can be eliminated. Saturated fats are higher in energy than unsaturated fats, making choice C correct.

122. A polar solute is poured into a container with a nonpolar solvent. Which of the following statements best describes the reaction? OA) The strong dipoles of the polar molecules separate the weak bonds between the nonpolar molecules. OB) The dipoles of the polar molecules are too weak to break the bonds between the nonpolar molecules. OC) The instantaneous dipoles of the nonpolar molecules are too weak to separate the bonds between the polar molecules. OD) The instantaneous dipoles of the nonpolar molecules separate the bonds between the polar molecules.

OC) The instantaneous dipoles of the nonpolar molecules are too weak to separate the bonds between the polar molecules. If a polar solute and non-polar solvent are mixed, no solution will be formed (remember 'like dissolves like'). Choices A and D describe what would happen if this could successfully form a solution. This is not the case so either choice B or C must be correct. Polar molecules have stronger dipoles so choice B is not true.

141. A galvanic cell is prepared with solutions of Mg2+ and Al3+ ions separated by a salt bridge. A potentiometer reads the difference across the electrodes to be 1.05 V. The following standard reduction potentials at 25°C apply: Al3+ + 3e- ----> AI - 1.66 Mg 2+ + 2e- ----> Mg -2.37 Which of the following statements is true concerning the galvanic cell at 25°C? OA) Magnesium is reduced at the cathode. OB) The concentrations of ions are 1M. OC) The reaction is spontaneous. OD) For every aluminum atom reduced, an equal number of magnesium atoms are oxidized.

OC) The reaction is spontaneous. Reactions in galvanic cells are always spontaneous, thus their electric potentials are always positive. To find the reaction for this cell we must flip the more negative half reaction, in this case Mg, to get a positive electric potential. Al3+ + 3e- --> AI Eo =-1.66 Mg--> Mg2+ + 2e- Eo = + 2.37 Now we have a spontaneous cell with a positive electric potential (-1.66 V + 2.37 V = 0.71 V). We also have to multiply the aluminum reaction by 2 and the magnesium reaction by 3 to balance the electrons that are being produced. Notice, however, that we do not multiply their potentials. 2Al3+ + 3Mg --> 3Mg2+ + 2Al Eo =0.71 v Since 2 Al atoms are reduced for every 3 Mg atoms oxidized, choice Dis incorrect. We are given that the potential for this cell is 1.05 V. Since it does not equal the electric potential we calculated the conditions must not be standard. Thus, choice B is incorrect. Magnesium is oxidized, so choice A is incorrect.

74. Immediately upon bringing a hot piece of metal into a room, the heat is felt from 5 meters away. This heat transfer is probably occurring through: OA) convection. OB) transduction. OC) radiation. OD) conduction.

OC) radiation. Heat, which is the movement of thermal energy, occurs via conduction, convection, or radiation, making B, transduction, incorrect. Conduction is transfer via molecular collisions, or physical contact. Conduction through the air is inefficient and would take a very long time, eliminating choice D. Convection is transfer of thermal energy via fluid (gas or liquid) movements, such as air current or a breeze, which is not mentioned in the question, eliminating choice A. Radiation is transfer via EM waves, or light. The speed of light is 3 x 10^8 m/s, which would allow for the heat to be felt instantaneously, making choice C the correct explanation.

124. When two pure liquids, A and B, are mixed, the temperature of the solution increases. All of the following must be true EXCEPT: OA) the intermolecular bond strength in at least one of the liquids is less than the intermolecular bond strength between A and B in solution. OB) the reaction is exothermic. OC) the vapor pressure of the solution is less than both the vapor pressure of pure A and pure B. OD) the rms velocity of the molecules increases when the solution is formed.

OC) the vapor pressure of the solution is less than both the vapor pressure of pure A and pure B. The vapor pressure of solution will be in between the vapor pressures of the two pure substances, thus choice C is an incorrect statement. We are told that the temperature of the solution increases so we can assume that forming the solution was exothermic. Thus, the new intermolecular bonds between solvent and solute are more stable than the old intermolecular bonds within the solvent and solute. So choices A and Bare correct statements. The rms velocity is related to the temperature. Since temperature increases so does rms velocity, and choice D is a correct statement.

105. 20 g ofNaCI is poured into a coffee cup calorimeter containing 250 mL of water. lfthe temperature inside the calorimeter drops l oc by the time the NaCI is totally dissolved, what is the heat of solution for NaCl and water? (The specific heat of water; is 4.18 Jig 0 C.) OA) - 3 kJ/mol OB) -1kJ/mol OC) I kJ/mol OD) 3 kJ/mol

OD) 3 kJ/mol First figure out the heat evolved by the reaction using q = mcdeltaT. Remember that the density of water is 1 g/mL so 250 mL of water will have a mass of 250 g. q = mcdeltaT = 250 grams x 4.18 J/gC x 1C= 1050 joules. Notice that all the choices are given per mole of NaCl. One mole of NaCl weighs 57 grams so 20 grams is about 1/3 of a mole. Next divide by moles. This gives 3150 joules, which is equal to 3 kJ. Since the temperature went down, the reaction is endothermic with a positive enthalpy. Notice all the row1ding as these types of problems can often be done with very little math.

113. To prevent 'the bends,' scuba divers need to know the partial pressure of nitrogen duri ng their dive. At sea level the atmosphere is composed of approximately 78% nitrogen, 21% Oxygen, and l% other gases. What is the partial pressure ofNitrogen at an ocean depth of 100m? OA) 2.3 atm OB) 7.7 atm OC) 7.9 atm OD) 8.5 atm

OD) 8.5 atm By Dalton's law the total pressure at 100 meters will be equal to the sum of the partial pressures of the individual gases. The pressure at 100 meters is given by P = pgh, where p is the density of water (1000 kg/m3), g is gravitational acceleration (10 mM), and his the depth below sea level here 100 m. P= (1000 kg/m3) (10 m/s2) (100m) = 106 Pa. Then, the atmospheric pressure must be accounted for: P = 106 Pa + 101,325 Pa = 1.1 x 106 Pa. Since 78% of the pressure is nitrogen, by Dalton's law the partial pressure is: 0.78x1.1x106 Pa= 8.5x105 Pa or about 8.5 atm

93. A chemical cold pack contains a membrane separating water and ammonium nitrate. When the membrane is broken, the compounds react, cooling the mixture. At standard state, the equilibrium constant K: OA) =0 OB) =1 OC) <I OD) >1

OD) >1 When the membrane is broken, the compounds mix and react without outside energy, making the reaction spontaneous < 0). Even though this reaction is endothermic (deltaH > 0), recall that a reaction can still be spontaneous based on entropy (delta G= deltaH- T deltaS) at standard state, a spontaneous reaction must have an equilibrium constant K > 1, which is D. K < 1 indicates a reaction that is non-spontaneous, eliminating A and C. K = 1 indicates a reaction that is in equilibrium at standard state, which is not true of this reaction, otherwise heat would not be absorbed. Therefore, B is also incorrect.

137. Which of the following statements about a galvanic cell is false? OA) If Eo =0, a reaction may still be spontaneous depending upon the chemical concentrations. OB) A galvanic cell with a positive potential can perform work. OC) Reduction takes place at the cathode. OD) A salt bridge balances the charge by allowing positive ions to move to the anode

OD) A salt bridge balances the charge by allowing positive ions to move to the anode Positive ions move across the salt bridge to the cathode. This can be memorized by considering that the salt bridge is used to balance the charges. Since negative electrons move to the cathode, positive ions must balance the charge by also moving to the cathode.

54. Which of the following solvents is most likely to promote an alcohol to behave as a leaving group? OA) Carbon Tetrachloride OB) Ether OC) Acetone OD) Acetic Acid

OD) Acetic Acid Alcohol is not normally a good leaving group. In order to behave as a leaving group, it needs to be protonated COH2 is an excellent leaving group). The solvent that best promotes alcohol behaving as a leaving group is the solvent most likely to protonate the alcohol. Carbon tetrachloride, ether, and acetone are all aprotic solvents, meaning they do not donate protons to the reaction and are thus incapable of protonating alcohol. Choices A, B, and Care incorrect. Acetic acid, which is a protic solvent and an acid, will protonate an alcohol and help it behave as a leaving group.

80. As the temperature of hydrogen gas in a sealed container is increased, which of the following occurs? OA) A decrease in the random translational energy, decreasing pressure OB) A decrease in the random translational energy, increasing pressure OC) An increase in the random translational energy, decreasing pressure OD) An increase in the random translational energy, increasing pressure

OD) An increase in the random translational energy, increasing pressure The kinetic energy of molecules of a gas is directly proportional to the temperature, as given by KE = 3/2RT. Therefore, increasing the temperature will increase the random translational energy of the gas molecules, eliminating A and B. If the molecules have a higher kinetic energy, they would be moving faster, hitting the walls of the container more frequently, causing as increase in pressure. Another way to determine the effect of temperature on pressure is to use the ideal gas law, PV = nRT. Increasing the temperature while holding the volume constant will cause the pressure to increase, making C incorrect.

25. Of the bonds listed in the table below, the most stable bond is between : bond ---- energy C2H5-Cl 339 C2H5-CH3 356 H2C=CH-Cl 352 H2C=CH-CH3 385 C6H5-Cl 360 C6H5-CH3 389 OA) C2H5-Cl OB) C2H5-CH3 OC) C6H5-Cl OD) C6H5-CH3

OD) C6H5-CH3 The most stable bond is the bond with the highest bond energy. Remember, bond energy is the total energy required to break a compound into its constituent atoms divided by the number of bonds in that compound. In other words, it is a measure of average bond strength within a molecule. Bond energy is actually negative potential energy, so the higher the magnitude, the lower the energy of the compound, the more energy necessary to break the bond, and the more stable the bond. The highest bond energy is between the methyl group bonded to a ring structure; therefore, choice Dis the best answer. All other choices can be eliminated, as they all have lower bond energies than choice D.

17. All of the following may be true concerning catalysts and the reactions which they catalyze EXCEPT: OA) Catalysts are not used up by the reaction. OB) Catalysts lower the energy of activation. OC) Catalysts increase the rate of the reverse reaction. OD) Catalysts shift the reaction equilibrium to the right.

OD) Catalysts shift the reaction equilibrium to the right. Catalysts increase the rate of the reverse reaction as well as the forward reaction, often by lowering the activation energy of each. Catalysts do not directly affect the equilibrium of a reaction and are not used up in or produced by the reaction. Catalysts, for example, enzymes, are very likely to be tested.

99. At STP, one liter of which of the following gases contains the most molecules? OA) H2 OB) He OC) N2 OD) Each gas contains the same number of molecules at STP .

OD) Each gas contains the same number of molecules at STP . Unless otherwise indicated, assume that all gases behave ideally. The ideal gas law states that n =PVI RT. Therefore, at standard temperature and pressure, equal volumes of ideal gases contain the same number of gas molecules, ruling out choices A, B, and C. If these volumes contain the same number of moles, then they will contain the same number of molecules as well; the number of molecules equals Avogadro's number times the number of moles. Thus choice D is correct.

73. Which of the following is true concerning an air conditioner that sits inside a thermally sealed room and draws energy from an outside power source? OA) It will require more energy to cool the room than if part of the air conditioner were outside the room. OB) It will require more time to cool the room than if part of the air conditioner were outside the room. OC) It will require less energy to cool the room than if part of the air conditioner were outside the room. OD) It cannot cool the room on a permanent basis.

OD) It cannot cool the room on a permanent basis. The second law of thermodynamics states that a heat engine cannot have 100% efficiency in converting heat to work in a cyclical process. An air conditioner is a heat engine running backwards. Thus an air conditioner must expel more heat than it takes in when it runs perpetually (heat generated> heat extracted). Choice B is incorrect because as time passes, more heat will be generated, making the room warmer, not cooler. A specially made air conditioner could initially cool the room, but to cool the room permanently, it must expel the heat to a heat reservoir outside the room. However, the amount of energy required would be the same, eliminating choices A and C.

56. In the reaction above, ifKI were added directly to cyclopentanol without the use of a tosylate, what would be the major product? OA) S- iodocyclopentane OB) R- iodocyclopentane OC) Racemic mixture of S- and R- iodocylcopentane OD) No reaction

OD) No reaction This question requires an understanding of the purpose of the tosylate group used in step one. The tosylate plus oxygen act as a leaving group in step two- the purpose of using this molecule was to make the alcohol a better leaving group for the reaction with K-I. In the absence of a tosylate, the hydroxyl group will not act as a leaving group unless another compound (like an acid) is added to make leaving more favorable. The question stem does not indicate that any other molecule beside K-I is present, however, so no reaction will occur. It is tempting after reading this question to begin figuring out the chirality of each product and reactant, so trying to eliminate the "odd man out" answer choice before moving on the others can be very beneficial. In this case, it cannot be eliminated and leads to the correct answer. Answer: No reaction. There is no acid to make the alcohol a good leaving group, so no reaction will occur.

87. The condensation of water is shown. H20(g)-> H20(l) Which of the following will be positive for the condensation of water at 25°C and I atm? OA) delta H OB) delta S OC) delta G OD) None of the above

OD) None of the above Bonds are formed when water condenses, so energy is released and deltaH is negative. The water molecules become less random, so deltaS is negative. Condensation occurs spontaneously at 25°C (water is a liquid at room temperature), so llG is negative. Notice that this question can be answered without any numbers.

108. Substance A has a greater heat capacity than substance B. Which of the following is most likely true concerning substances A and B? OA) Substance A has larger molecules than substance B. OB) Substance B has a lower boiling point than substance A. OC) At the same temperature, the molecules of substance B move faster than those of substance A. OD) Substance A has more methods of absorbing energy than substance B.

OD) Substance A has more methods of absorbing energy than substance B. The heat capacity doesn't provide anything about the molecular size of an substance. Heat capacity is the amount of energy required to raise the temperature of the substance by a certain amount. Boiling point is dependent on vapor pressure not heat capacity. Imaging that substance A is water and substance B is ice. That would satisfy the question stem, but water and ice have the same boiling point. Choice C mistakenly relies upon speed and not kinetic energy for temperature. Choice Dis the correct choice by process of elimination. The more ways that a substance has to absorb energy, the more heat it can absorb with the least change in temperature.

83. For a particular reversible reaction, the forward process is exothermic and the reverse process is endothermic. Which of the following statements must be true about this reaction? OA) The forward reaction will be spontaneous under standard conditions. OB) The reverse reaction will be spontaneous under standard conditions. OC) The activation energy will be greater for the forward reaction than for the reverse reaction. OD) The activation energy will be greater for the reverse reaction than for the forward reaction.

OD) The activation energy will be greater for the reverse reaction than for the forward reaction. The reaction coordinate below shows the energy of activation for an endothermic reaction is greater than for an exothermic reaction. Choices A and B cannot be determined without knowing the change in entropy.

139. A negative cell potential indicates which of the following? OA) Both half reactions are nonspontaneous. OB) The reduction half reaction potential is greater than the oxidation half reaction potential. OC) The oxidation half reaction potential is greater than the reduction half reaction potential. OD) The cell is electrolytic.

OD) The cell is electrolytic. Although a both a Galvanic cell and an electrolytic cell can have a positive potential, only an electrolytic cell can have a negative potential.

77. A rigid container of constant volume is used to store compressed gas. When gas is pumped into the container, the pressure of the gas inside the container is increased and the temperature of the container also increases. Which statement is true of the work done on the container? OA) The work is equal to the increase in the pressure inside the container. OB) The work is equal to the increase in the temperature inside the container. OC) The work is equal to the sum of the pressure and temperature increases. OD) There is no work done on the container.

OD) There is no work done on the container. The work done by or on a gas is given by w = P deltaV(constantpressure)· Because pressure is not constant, calculus would be needed to solve this problem. However, the container is rigid and has a constant volume, making deltaV = 0, resulting in zero work.

142. A concentration cell contains 0.5 M aqueous Ag+on one side and 0.1 M aqueous Ag+on the other. All of the following are true EXCEPT: OA) electrons will move from the less concentrated side to the more concentrated side. OB) electrons will move from the anode to the cathode. OC) as the cell potential moves toward zero, the concentrations of both sides will tend to even out. OD) delta G > 0

OD) delta G > 0 A concentration cell is a special type of galvanic cell where the two half reactions in the half cells are the exact reverse of each other. Like a galvanic cell, a concentration cell is always spontaneous, so < 0.. The concentrations in the cell even out at equilibrium, a cell potential of zero. Choices A and B state the same thing, thus neither could be the correct answer.

121. The air we breathe is approximately 21 % 0 2and 79% N2. If the partial pressure of nitrogen in air is 600 torr, then all of the following are true EXCEPT: OA) the mole fraction of nitrogen in air is 0.79. OB) the mass of nitrogen in a 22.4 L sample of air is 22.1 grams at 0°C. OC) the partial pressure of oxygen is approximately 160 torr. OD) for every 21 grams of oxygen in an air sample, there are 79 grams of nitrogen.

OD) for every 21 grams of oxygen in an air sample, there are 79 grams of nitrogen. 1 atm is equivalent to 760 torr. Since the partial pressure of nitrogen is 600, the mole fraction of nitrogen is 0.79. X N2 = P Nz f P t ot = 6 0 0 t o r r / 7 6 0 t o r r = 0 . 7 9 . Since this is the same as the percentage given in the question stem we know that those percentages are by particle and not by mass. Choice D would be true if the percentages were based on mass. Choice A is true based on our calculations above. Choice B is true as it restates what we know about standard temperature and pressure. Since the two partial pressures have to add to the total, then the partial pressure of oxygen is 760 torr- 600 torr = 160 torr.

132. All of the following are always true concerning oxidation reduction reactions EXCEPT: OA) an atom in the reducing agent is always oxidized. OB) if reduction takes place, so must oxidation. OC) an atom in the oxidizing agent gains electrons. OD) if an atom of the reductant loses two electrons, an atom of the oxidant gains two electrons.

OD) if an atom of the reductant loses two electrons, an atom of the oxidant gains two electrons. An example of where this is false is in Question 11: 2HCI+Zn->ZnCh+H2 Here each atom of the reducing agent, zinc, loses two electrons, and the hydrogen atom of the oxidizing agent, HCl, gains one electron. To balance the equation there must be two hydrogens for each zinc. Choices A and Bare both true statements, and state the same thing. Choice Cis a true statement, based on LEO roars GER.

160. When solid sodium acetate, NaC2H3O2, is added to pure water, the pH of the solution will: OA) decrease, because Na+acts as an acid. OB) increase, because a+acts as a base. OC) decrease, because C2H3O2- acts as an acid OD) increase, because C2H3O2- acts as a base.

OD) increase, because C2H3O2- acts as a base. Acetate ion, C2H30 2-, is the conjugate base of a weak acid, so it will act as a base in solution. Sodium ion, Na+, is the conjugate acid of a strong base, so it is neutral in solution. The result of a base and a neutral compound in solution is a basic solution, or a pH over 7. This means that the pH will increase from the initial value of 7 due to the contribution from the acetate ion.

95. The combustion of propane is given by the following exothermic reaction: C3H8(g) +5O2 --> 3CO2(g) +4H2O(g) For the above reaction, each of the following wi ll increase the production of heat EXCEPT: OA) high pressure and high temperature. OB) high pressure and low temperature. OC) low pressure and high temperature. OD) low pressure and low temperature.

OD) low pressure and low temperature. In order to increase the production of heat, the reaction must shift towards the right and generate products. Increasing the temperature will cause a leftward shift, which is opposite the desired effect, eliminating choices A and C. The effects of pressure change are dependent on the moles of gas of the reactants vs. products. Looking only at gases (which are all the compounds in this reaction), 6 moles of reactants generates 7 moles of products. A decrease in pressure shifts the reaction toward the side with more moles of gas, in this case, the products. Therefore, a low pressure and low temperature will increase the production of heat, eliminating choice B and leaving choice 0 as the correct answer.

119. At atmospheric pressure, the temperature of a pot of boiling water remains at 100°C, when heat is added. The best explanation as to why the added energy does not raise the temperature is that: OA) at the boiling point, the large heat capacity of water allows water to absorb the added energy. 08) the hydrogen bonds of water are strong enough to absorb the added energy without breaking. OC) as the water becomes steam, the added energy becomes kinetic energy of the gas molecules. OD) the added energy is used to break bonds between water molecules.

OD) the added energy is used to break bonds between water molecules. At the boiling point, any added energy is used to break intermolecular bonds and not to increase kinetic energy, so, while the water is boiling, there is no temperature increase.

entropy

On the MCAT®, if a reaction increases the number of gaseous molecules, that reaction has positive entropy for the reaction system (but not necessarily for the surroundings or the universe). This is because gas particles are more free to move around than are solid or liquid particles and thus can spread their energy more freely. The greater the temperature of a substance, the greater is its entropy. Among molecules that are in the same phase, the larger molecule (more bonds) has a higher entropy at a given temperature. *Other factors being equal, the entropy of a gas is much higher than the entropy of a liquid, which is higher than the entropy of a solid.* *Zero-point enthalpy is based on a scale created relative to common chemical reactions. Zero-point entropy is based on an absolute scale rather than a relative scale.* *In practice, absolute entropy is unattainable. Pure substances in equilibrium are assigned an entropy approaching zero as they approach 0 Kelvin. For the think of entropy as nature trying to spread energy evenly throughout the universe.* *The point of equilibrium is the point of maximum universal entropy. Since the entropy of an isolated system cannot decrease, the universal entropy change for any reversible reaction must be zero in both directions.*

cell potential (E)=electromotive force (emf)

Only potential differences between chemically identical forms of matter are easily measurable, so the two terminals of a galvanic cell must be made of the same material. The cell potential (E), also called the electromotive force (emf), is the potential difference between the terminals when they are not connected. Connecting the terminals reduces the potential difference due to internal resistance within the galvanic cell. The drop in the emf increases as the current increases. The current from one terminal to the other is defined as moving in the direction opposite the electron flow. Since electrons in the anode have higher potential energy than those in the cathode, electrons flow from the anode to the cathode *electrons are negatively charged, so they are attracted to the positive cathode and repelled by the negative anode in a galvanic cell.* *Sketch a couple of your own galvanic cells so that you understand how they are made. Notice that the concentrations are 1 M. This rep- resents standard conditions. When the concentrations are 1 M, the values from the reduction half reaction table can be used to calculate the cell potential. The Nernst equation can be used to find the cell potential when the concentrations are not 1 M, as will be discussed later in this section.*

oxidation reduction neither oxidation nor reduction

Oxidation: increase in bonds to oxygen or halogen, loss of C-H bonds. Reduction : increase in bonds to hydrogen or R groups, loss of bonds to oxygen or halogen. Neither oxidation nor reduction: addition or loss of H+, H2O, HX, etc . oxidation of C in CO2? 4+ oxidation of C in formic acid (H-(C=O)-OH)? 2+ oxidation of C in formaldehyde (H-(C=O)-H)? 0 oxidation of C in methanol? -2 oxidation of C in methane CH4? -4

Paramagnetic elements Diamagnetic elements

Paramagnetic elements: elements with unpaired electrons (e.g. Li), meaning that a subshell is not completely filled. The spin of each unpaired electron is parallel to the others. As a result, the electrons will align with an external magnetic field. Diamagnetic elements: are elements with no unpaired electrons (e.g. He), meaning their subshells are completely filled. They are unresponsive to an external magnetic field.

Q < K Q = K Q > K *if K =1 then deltaGo =0 if K > 1 then deltaGo < 0 if K < 1 then deltaGo > 0* * This is is pretty tricky stuff, but it's worth racking your brains and killing some time on it now rather than on the MCAf®. Reread this section and make sure that you understand the relationships between K, Q, deltaGo, delta G, and T.*

Q < K Forward reaction Q = K equilibrium Q > K reserve reaction *In some cases, the forward reaction is so much more favorable than the reverse reaction that,for all practical purposes,the reaction runs to completion. Alternatively, if a product is continually removed as the reaction proceeds (perhaps in the form of a gas leaving an aqueous solution), the reaction can run to completion .*

143. According to the Nernst equation: if a concentration cell has a potential of 0.12 V, and a concentration of 0.1 M Ag+ at the anode, what is the concentration of Ag+at the cathode? OA) 10^-3 M OB) 10^-1 M OC) lM OD) 10M

Q=x/y OD) 10M In this cell the cathode has the greater concentration because electrons flow toward it to reduce the number of cations. Also in a concentration cell Eo = 0, since the reduction half reaction is simply the exact reverse of the oxidation half reaction. n = 1 because only one electron is transferred in each reaction. x/y must be a fraction so that the log will be negative and E will be positive. Thus we have: E = 0 - (0.06/1)log(0.1/y) = 0.12 V -2 = log(0.1/y) y = 10 so that x/y = 10^-2.

Quantum mechanics

Quantum mechanics : ays that elementary particles can only gain or lose energy in discrete units. This is analogous to walking up stairs as opposed to walking up a ramp. Someone walking up the stairs can only move up or down in discrete units, defined by the height of each step. If the steps are each 25 em tall, the person will never be 17 em above the ground. Someone using a ramp moves continuously upward, and can be at 17 em, 25 em, or 111.2 em above the ground; this person is not limited to discrete units. In quantum mechanics the 'steps' are discrete quanta of energy. Each 'step' or energy unit is very small, and is only significant when dealing with elementary particles.

Hydrolysis of carboxylic acid derivatives R-(C=O)-Cl +H2O--> acid chloride R-(C=O)-OR +H2O--> ester R-(C=O)-NHR +H2O--> amide R-(C=O)-O-(C=O)-R +H2O--> anhydride

R-(C=O)-Cl +H2O--> R-(C=O)-OH +HCl acid chloride R-(C=O)-OR +H2O--> R-(C=O)-OH +ROH ester R-(C=O)-NHR +H2O--> R-(C=O)-OH +RNH2 amide R-(C=O)-O-(C=O)-R +H2O-->R-(C=O)-OH +RCOOH anhydride

acid halide +... RCOOH H2O ROH RNH2

RCOOH --> anhydride H2O --> carboxylic acid ROH --> ester RNH2 --> amide

common ion effect

The F- ions do affect the equilibrium because F- is included in the equilibrium expression. Their disturbance of the equilibrium is called the common ion effect because it involves an ion in "common" with an ion in the equilibrium expression. According toLe Chatelier's principle, the addition of a common ion pushes the equilibrium in the direction that will reduce the concentration of that ion. In this case, the equilibrium would move to the left in order to decrease the concentration of BaF2, reducing the solubility ofBaF2. *A common ion added to a saturated solution shifts the equilibrium, increasing the amount of precipitate. It does NOT affect the value of Ksp· A common ion added to a solution that is not saturated does NOT shift the equilibrium, because in an unsaturated solution, there is no equilibrium to shift*

effective charge

The amount of charge felt by the most recently added electron is called the effective nuclear charge (Z.u)· In complete shielding, each electron added to an atom would be completely shielded from the attractive force of all the protons except for the last proton added, and the Zeff would be 1 eV for each electron. Without shielding, each electron added would feel the full attractive force of all the protons in the nucleus, and the Zeff would simply be equal to Z for each electron. notice that Zeff drops going from neon to sodium. This happens because the new electron is added to an entirely new shell, the 3s subshell. This causes a strong increase in shielding and reduction in Zeff, but the outermost electron in sodium still experiences a higher Zeff than the outermost electron of the element immediately above it on the periodic table, lithium. This is because the effects of the more strongly charged nucleus outweigh the shielding effect that an additional electron shell can provide. A similar drop also occurred between He and Li, though it was not quite as large because there were fewer protons and electrons involved.

decarboxylation

The final important oxidation reaction is the oxidation of a carboxylic acid to carbon dioxide gas.

lower, the Ksp, then the solid will precipitate first

The solubility product, Ksp is the equilibrium constant for the solvation reaction. As with all equilibrium constants, it is calculated as [products]/[reactants]. Thus, the smaller the equilibrium constant the smaller the proportion of products formed compared to the reactants. For solubilities, the smaller the Ksp the less soluble the compound. The least soluble compound will be the first to precipitate. Here BaSO4 has the smallest Ksp so it will be the first to precipitate.

weak acids weak bases

WEAK ACIDS HF HCN CH3COOH H2O WEAK BASES NH3 NH4OH C5H5N H2O

Raoult's law

When a *nonvolatile solute* (a solute with no vapor pressure) is added to a liquid, some solute molecules reach the surface of the solution and reduce the surface area available for the liquid molecules. Since solute molecules do not break free from the solution but do take up surface area, the number of molecules breaking free from the liquid decreases while the surface area of the solution and the volume of open space above the solution remain the same. Thus the vapor pressure of a solution is lower than the vapor pressure of the pure solvent. According to the ideal gas law, PV = nRT, n and P are proportional at constant volume and temperature. This means that the vapor pressure of the solution Pvis proportional to the vapor pressure of the pure liquid P. and the mole fraction of the liquid x., meaning the ratio of moles solvent to total moles of solution, as given by Raoult's law The sum of the partial vapor pressures is equal to the total vapor pressure of the solution, giving a modified form of Raoult's law: P=XaPa + Xb+Pb *Raoult's law for nonvolatile solutes: If 97% of the solution is solvent, the vapor pressure will be 97% of the vapor pressure of the pure solvent. Raoult's law for volatile solutes: If 97% of the solution is solvent, the vapor pressure will be 97% of the vapor pressure of the pure solvent PLUS 3% of the vapor pressure of the pure solute.*

aldol condensation

a carbonyl nucleophile attacks another carbonyl. A new bond is formed between the a-carbon on one molecule (which preserves its carbonyl) and the carbonyl carbon on the other molecule (which is reduced to an alcohol). *When you see a carbonyl reaction, ask yourself if the carbonyl was attacked (more common) or if the carbonyl was the attacker. If you see a change in what was attached to the carbonyl carbon, the carbonyl carbon was attacked by a nucleophile ana either an aaaition (alaehyae or ketone becomes an alcohol) or a substitution reaction (carbonyl with a new leaving group) took place. If the original carbonyl is intact with a new bona to the alpha carbon, the *alpha carbon* of the carbonyl acted as a nucleophile (carboxylate or enolate).* *Aldol condensation is one of the reactions of glycolysis. The reverse of this reaction is a **retro-aldol** reaction, which is what splits the ATP activated glucose in half.*

salt bridge

a type of liquid junction that minimizes this potential difference. Typically a salt bridge is made from an aqueous solution of KCl. The salt bridge allows movement of ions between solutions without creating a strong extra potential within the galvanic cell. It minimizes the potential because the K' ions move toward the cathode at about the same rate that the Cl- ions move toward the anode. *Here is exactly what's going on in the galvanic cell diagram in Figure 6 .10. The solid zinc atoms would like to get rid of their electrons, but they need a place to put them. The Cu2+ ions in solution are happy to take them. This creates a potential difference. The question is how to transfer electrons without building up a charge difference, because separating charges is energy expensive. The copper wire gives the electrons a path with low resistance to flow, but the electrons won't flow if they are building up a charge difference. The salt bridge allows ions to move (negative ions toward the anode and positive ions toward the cathode) and carry away any charge buildup. As electrons leave the solid zinc strip, Zn2+ ions are formed and dissolve into solution. At the cathode, Cu2+ ions gain the electrons coming through the wire and form solid Cu.*

90. Nitric acid is produced commercially by oxidation in the Oswald process. The first step of this process is shown below. 4NH3 (g) + 5O2 (g) <---> 4NO (g) + 6H2O (g) A container holds 4 moles of gaseous ammonia, 5 moles of gaseous oxygen, 4 moles of gaseous nitric oxide, and 6 moles of water vapor at equilibrium. Which of the following would be true if the container were allowed to expand at constant temperature? a) Initially during the expansion the forward reaction rate would be greater than the reverse reaction rate. b) The equilibrium would shift to the left. c) The partial pressure of oxygen would increase. d) The pressure inside the container would increase.

a) Initially during the expansion the forward reaction rate would be greater than the reverse reaction rate. Expansion of the container increases the volume and decreases the pressure, so choice D is incorrect. By Le Chatelier's principle, a decrease in pressure shifts the reaction to the side with more moles of gas. In this problem, the ratio of the moles of gas in terms of reactants to products is 9 to 10. As a result, the equilibrium would shift to the right by increasing the forward reaction rate, eliminating choices Band C and leaving choice A as the correct answer.

79. Which of the following is a type of kinetic energy? a) Vibrational energy b) Chemical energy c) Rest mass energy d) Intermolecular energy

a) Vibrational energy Like macroscopic energy, microscopic energy can be divided into kinetic and potential energy. Kinetic energy is a result of motion, such as vibrational energy, making choice A the correct answer. Electronic, rest mass, and intermolecular energy are examples of potential energy, energy that is stored in some form, at the microscopic scale. Therefore choices B, C, and D are incorrect.

24. The mass number of an atom undergoing radioactive decay will remain unchanged in each of the processes below EXCEPT: a) alpha decay. b) beta decay. c) electron capture. d) gamma decay.

a) alpha decay. In alpha decay, a particle identical to a helium nucleus is released, and, therefore, the mass number decreases by four. None of the other processes changes the mass number.

absolute configuration relative configuration *Know that enantiomers have the same chemical and physical characteristics except for two cases: 1. interactions with other chiral compounds; 2. interactions with polarized light.*

absolute configuration: R or S relative configuration: two molecules have the same relative configuration about a chiral carbon if they differ by only one substituent and the other substituents are oriented identically about the carbon

hemiacetal

aldehyde+ alcohol --> hemi acetal ketone+ alcohol --> hemiketal alcohol is the nucleophile When additional alcohol- R OH - is added to the hemiacetal or hemiketal, the OR group can replace the OH group, forming an *acetal* or a ketal. Acetals and ketals have two OR groups attached to what was previously the carbonyl carbon.

hemiketal

aldehyde+ alcohol --> hemi acetal ketone+ alcohol --> hemiketal alcohol is the nucleophile When additional alcohol- R OH - is added to the hemiacetal or hemiketal, the OR group can replace the OH group, forming an *acetal* or a ketal. Acetals and ketals have two OR groups attached to what was previously the carbonyl carbon.

aldose ketose

aldose: carbohydrates + aldehydes ketose: carbohydrate + ketones

tautomerization alpha carbon

alpha carbon: any carbon attached directly to a carbonyl carbon *There are other forms of tautomeriza- tion, but keto-enol tautomerization is the most likely to be tested on the MCAT. To recognize other forms, simply watch for the proton shift. The two molecules exist in equilibrium. They are NOT resonance structures.*

trend of reactivity of carbonyls least to most

amide carboxylic acid acid anhydride and ester ketone-undergo addition not substitution aldehyde-undergo addition not substitution acid halide *Compare the groups attached- are they with- drawing or donating? - CI is very withdrawing. -H in the aldehyde is neutral. The R group in the ketone is somewhat donating. For this reason, aldehydes are more electropositive and there- fore more reactive than ketones. The lone pair on the oxygen in the carboxylic acid and ester donate into the carbonyl carbon. The lone pair on the nitrogen in the amide is even more strongly donating. Therefore an amide is least reactive.*

144. A spoon is plated with silver in an electrolytic process where the half reaction at the cathode is: Ag+ (aq) + e- --> Ag (s) Eo=0.8 V If the current i is held constant fort seconds, which of the following expressions gives the mass of silver deposited on the spoon? (F is Faraday's constant.) a) 107.8 itF b) 107.8 (it)/F c) 107.8 i (tF) d) 107.8 (iF)/t

b) 107.8 (it)/F Use units to solve the problem. We want to go from current to grams. Current is Coulombs/sec. F is coulombs per mole of electrons. From the balanced equation we can see that for every mole of electrons there is one mole of silver. The molecular weight of silver is 107.8 g/mol. (Coulombs/sec) x (sec) x (mol/Coulombs) x (grams/mol)= grams i x t x (1/F) x 107.8 =grams

168. The acid dissociation constant for HC6H7O6 is 8.0x10^-5. If a solution contains equal concentrations of HC6H7O6 and C6H7O6-, what will be the pH of the solution? a) 3.0 b) 4.1 c) 5.3 d) 9.0

b) 4.1 he Henderson-Hasselbalch equation shows that when a weak acid and its conjugate base are present in a solution in equal amounts, the pH will be equal to the pK. of the conjugate acid. This is because of the log of 1 is 0. The negative logarithm of 8.0 x 10^-5 is between 4 and 5, narrowing down the answer to choice B.

boyle's law charles' law avogadro's law

boyle's law: PV=constant charles' law: V/T = constant *Special cases of the ideal gas law include: 1) Charles' law: The volume ofa gas is proportional totem- perature at constant pressure; 2) Boyle's law: The volume of a gas is inversely proportional to pressure at constant temperature; and 3) Avogadro's law: The volume of a gas is proportional to the number of moles at constant temperature and pressure.* avogadro's law: V/moles=constant *Though Charles', Boyle's, and Avogadro's laws are important, it is more important to have a good understanding of the ideal gas law. PV= nRT will solve any problem that the other three laws might solve.*

bronsted-lowry acid-base lewis acid-base

bronsted-lowry acid-base: moves O and H lewis acid-base: moves H

21. The half-life of substance X is 45 years, and it decomposes to substance Y. A sample from a meteorite was taken which contained 1.5% of X and 13.5% of Y by mass. If substance Y is not normally found on a meteorite, what is the approximate age of the meteorite? a) 45 years b) 100 years c) 140 years d) 270 years

c) 140 years Since Y is not normally found in the meteorite, we assume that all of the Y came from the decomposition of X. Thus, the percentage of the sample that was X at the birth of the meteorite must have been the sum of the percentages of Y and X, or 15% (1.5% + 13.5% = 15%). The percentage of the sample that is X is now only 10% of that (or 1.5%). After the first half life there would have been 50% left; after the second half life, 25% left; after 3 half-lives, 12.5% left. Thus, a little more than 3 half-lives is required to reduce a substance to 10% of its original amount. Each half life is 45 years. 45 years times 3 half-lives gives 135 years. A little more than three half-lives are used, so the best answer is a little more than 135 years.

91. Which of the following is true concerning a reaction that begins with only reactants and moves toward equilibrium? a) The rates of the forward and reverse reactions decrease until equilibrium is reached. b) The rates of the forward and reverse reactions increase until equilibrium is reached. c) The rate of the forward reaction decreases and the rate of the reverse reaction increases until equilibrium is reached. d) The rate of the forward reaction increases and the rate of the reverse reaction decreases until equilibrium is reached.

c) The rate of the forward reaction decreases and the rate of the reverse reaction increases until equilibrium is reached. Initially, the reaction contains only reactants and no products, so the reverse reaction rate begins at zero. As the reactants are consumed, the forward reaction rate decreases while the reverse reaction rate increases, eliminating choices A, B, and D. At equilibrium, the rate of the forward reaction will be equal to the rate of the reverse reaction, so the forward decreases and the reverse increases until equilibrium, making C correct.

20. As temperature is increased in an exothermic gaseous reaction, all of the following increase EXCEPT: a) reaction rate. b) rate constant. c) activation energy. d) rms molecular velocity.

c) activation energy. Exothermicity concerns the thermodynamics of the reaction, and not the rate, so it can be ignored. The energy of activation is the energy required for a collision of properly oriented molecules to produce a reaction. This does not change with temperature. Rms velocity increases with temperature. Reaction rate increases with temperature because more collisions can take place at higher temperature as the molecules are moving faster. Rate constant is related to reaction rate so it, likewise, will increase with temperature.

78. All of the following are forms of internal energy EXCEPT: a)rotational energy. b) vibrational energy. c) chemical energy. d) translational energy.

c) chemical energy. Internal energy is the energy of molecules on a microscopic scale - all forms of energy excluding those related to the motion of the system as a whole. Rotational, vibrational, and translational energy are all examples of internal energy, therefore choices A, B, and Dare incorrect. Gravitational energy is an example of potential energy at the macroscopic scale, making choice C the correct answer.

buffer in solution

combinations of acids and salts that are used to keep the pH of a solution within a certain range. To make a buffer solution, we would start with an acid whose pKa is close to the pH at which we want to buffer the solution. Next we would mix equal amounts of that acid with its conjugate base. The concentration of the buffer solution should greatly exceed the concentration of outside acid or base that could affect the pH of the solution. So, a buffer solution is made from equal and copious amounts of a weak acid and its conjugate base. *Carbonic acid, H2C03, is a weak acid with a pKa of 6.37. Bicarbonate HC03 - is amphoteric (can act as an acid or a base), but will only act as a base when it makes up part of a buffer with carbonic acid.* *Don't worry if multiple acids or bases are added to the same buffer solution. The buffer will accept any excess protons or donate pro- tons to any excess hydroxides. All you must do to find the pH of the solution is to solve the Henderson- Hasselbalch equation.* *The carbonic acid/bicarbonate buffer is extremely important in the regulation of physiological pH in the human body. Carbon dioxide participates through the activity of the enzyme carbonic anhydrase, which catalyzes the reversible conversion of carbonic acid into water and carbon dioxide: CO2 + H2O <--> H2CO3 <--> HCO3- + H+*

concentration cell electrolytic cell

concentration cell: *The concentration cell is just a particular type of galvanic cell. It is never a t standard conditions, so the Nernst equation must be used to solve for the cell potential.* limited form of a galvanic cell in which a reduction half reaction takes place in one half cell while the exact reverse of that half reaction is taking place in the other half cell. The cells differ in their ion concentrations. electrolytic cell: created by hooking up a power source across the resistance of a galvanic cell and forcing the reactions to run in reverse. Any electrolytic cell on the MCAT®will have a negative emf. In the electrolytic cell, the cathode is marked negative and the anode is marked positive. Reduction still takes place at the cathode and oxidation at the anode. *The assignment of positive and negative to electrodes in galvanic and electrolytic cells is based upon perspective. Galvanic cells are used to provide energy to an external load, so the electrodes are labeled so that negative electrons are flow- ing toward the positive electrode. Electrons flow from the load to the cathode, so the cathode is labeled positive in the galvanic cell. The focus of electrolytic cells is within the cell itself. For instance, electrophoresis uses an electrolytic cell. Negatively charged amino acids within the electrolytic cell flow toward the positive electrode, so the anode is labeled positive in the electrolytic cell.* *Learn to diagram a galvanic cell. Once you can do that, other types of cells can be created from the galvanic cell. Remember that galvanic cells have a positive cell potential and electrolytic cells have a negative potential. Galvanic cells are spontaneous; electrolytic cells are forced by an outside power source. The term 'electrochemical' cell can mean either 'galvanic' or 'electrolytic' cell. For any and all cells, remember 'Red Cat, An Ox'. This translates to Reduction at the Cathode, Oxidation at the Anode.*

conduction convection radiation

conduction: thermal energy transfer via molecular collisions. It requires direct physical contact. In conduction, higher energy molecules of one system transfer some of their energy to the lower energy molecules of the other system via molecular collisions. Heat can also be conducted through a single object. *the order in which objects are placed makes no difference in conduction. For instance, whether a cold blanket is placed under a warm blanket or vice versa makes no difference to trapping heat.* convection: thermal energy transfer via fluid (i.e. liquid or gas) movements. In convection, differences in pressure or density drive warm fluid in the direction of cooler fluid. On a warm sunny day at the beach, for instance, the air above the land heats up faster than the air above the water. As the air above the land warms, it becomes less dense and rises, carrying its thermal energy with it. The cool air over the ocean moves in to fill the space over the land. The net result is a circular current of air carrying the heat generated by the hot beach up and out to the cooler ocean. Ocean and air currents are common examples of convection radiation: thermal energy transfer via electromagnetic waves. When metal is heated, it glows red, orange-yellow, white, and finally blue-white as the hot metal radiates visible electromagnetic waves. Even before the metal begins to glow, it radiates electromagnetic waves at a frequency too low to be visible to the human eye.

conformational isomers

conformational isomers- different spatial orientations for the same molecule. newman projections most potential energy is fully eclipsed> eclipsed> gauche> antistaggered

22. 216Po undergoes two alpha decays and two beta decays to form : a) 208Tl b) 224Ra c) 212Pb d) 208Pb

d) 208Pb Each of the answers shows an isotope of element and its associated mass number. Recall that mass number is the sum of the numbers of protons and neutrons. Because atomic number is a defining characteristic of an element, it can be inferred that each element has an atomic number equal to that shown on the periodic table. Therefore, 216Po has mass number 216 and atomic number 84. Recall that alpha decay is the loss of an alpha particle consisting of two protons and two neutrons, and beta decay is the conversion of a neutron into a proton, electron and neutrino. In order to determine the identity of the resulting atom, consider changes to the atomic number. Each alpha decay results in the loss of two protons, and each beta decay results in the gain of one proton. Thus, there is a net loss of two protons, meaning the new element has atomic number 82; the resulting atom is Pb. Therefore choices A and B can be eliminated. In order to decide between choices C and D, consider the changes that occur to the mass number. Each alpha decay results in a loss of four mass units whereas beta decay does not change the mass of the atom. Thus, there is a net loss of eight mass units, meaning the isotope has a mass number of 208; the resulting atom is 208Pb and choice D is the best answer.

66. Glucose reduces Tollens reagent to give an aldonic acid, ammonia, water, and a silver mirror. Methyl B-glucoside does not reduce Tollens reagent. Based on the structures shown below, which of the following best explains why methyl B- glucoside gives a negative Tollens test? a) Aldehydes are not oxidized by Tollens reagent. b) Ketones are not oxidized by Tollens reagent. c) Hemiacetal rings are stable and do not easily open to form straight chain aldehydes. d) Acetal rings are stable and do not easily open to form straight chain aldehydes.

d) Acetal rings are stable and do not easily open to form straight chain aldehydes. The Tollens test gives a silver mirror for reducing sugars. Reducing sugars are hemiacetals in their ring form and either aldehydes or ketones in their straight-chain form. Acetals do not open easily because they contain blocking groups. Methyl is an acetal. Choice A is incorrect because glucose is an aldehyde and reduces Tollens reagent. Choice B is irrelevant because neither sugar is a ketone. Additionally, Tollens reagent promotes enediol rearrangement of ketones to aldehydes. Choice Cis incorrect because glucose is a hemiacetal that opens to an aldehyde and reacts with Tollens reagent.

enthalpy standard state enthalpy of formation

delta H= delta U + P(delta V) at constant pressure U=E= internal energy P= pressure V=volume *Enthalpy cannot be understood intuitively. Just rely on the equation. For an ideal gas, enthalpy and internal energy depend ONLY on temperature. Enthalpy increases with temperature.* standard state enthalpy of formation: deltaH reaction = deltaH products - deltaH reactants *Remember that bond breaking requires energy and bond formation releases energy. This is true of all types of bonds: covalent, non-covalent, and ionic. It is also true for both intermolecular and intramolecular bonds. This concept will help you on the MCAT when you see unfamiliar reactions. But do not confuse exothermic and endothermic with spontaneous and non-spontaneous! Either can be spontaneous or non-spontaneous depending on other factors of the reaction, as will be discussed.*

diastereomers meso compound maximum number of optically active isomers =

diastereomers: have the same molecular formula, and same bond-to-bond connectivity, but are NOT mirror images of each other and are NOT the same compound. Unlike enantiomers, diastereomers with multiple chiral centers have the same absolute configuration at one or more of those chiral centers. meso compound: A meso compound is one that has multiple chiral centers, but is optically inactive. Meso compounds have a plane of symmetry through their center, which divides the molecule into two halves that are mirror images ofeach other. Because oftheir symmetry, the chiral centers offset each other and the overall compound does not rotate plane-polarized light. Meso compounds are considered to be achiral. 2^n

electric potential (E) reduction potentials

electric potential (E): Since electrons, which have charge, are transferred in a redox reaction, there is an electric potential (E) associated with any redox reaction. The more positive the potential, the more likely the reaction is to proceed. reduction potentials: Half reaction potentials are usually listed as reduction potentials. To find the oxidation potential for the reverse half reaction, the sign of the reduction potential is flipped.

standard reduction potentials

electric potentials (Don't need to memorize) 1.50 1.23 1.2 0.80 0.52 0.34 0 -0.036 -0.76 -0.83 going up: reactants in this direction are stronger oxidizing agents and more easily reduced going down: products in this direction are stronger reducing agents and more easily oxidized *Notice that the metals used to make coins have negative oxidation potentials (except for nickel). Unlike most metals, platinum, gold, silver, mercury, and copper do not oxidize (or dissolve) spontaneously under standard conditions in the presence of aqueous W . Also notice that Table 6.4 gives the reduction potential for Ag2+(aq) and the oxidation potential for Ag(s). (Warning:The table does not give the oxidation potential for Ag2+.) The strongest oxidizing agent is in the upper left hand corner of a reduction table. The strongest reducing agent is in the lower right hand corner of a reduction table. Notice that water is both a poor oxidizing agent and a poor reducing agent. Finally, notice that the second half reaction in Table 6 .4 is part of the final reaction in aerobic respiration, in which oxygen accepts electrons to form water. Predictably, this reaction has a high positive potential.* *2H+ + 2e- --> H2 Eo =0.00v*

emission line spectrum absorption line spectrum

emission line spectrum: When excited electrons fall from a higher energy state to a lower energy state, energy is released. This energy creates an emission line spectrum that is characteristic of the given element. absorption line spectrum: measures the radiation absorbed when electrons absorb energy to move to a higher energy state. E= hf wavelength = h/ mv

epimers anomers cis=E trans=Z

epimers: diastereomers that differ in configuration at only one chiral carbon. anomers: cyclic diastereomers that are formed when a ring closure occurs at an epimeric carbon. The chiral carbon of an anomer is called the *anomeric carbon*. As will be described in the next lecture, carbohydrates are classified according to their configuration at the anomeric carbon.

titration of weak acid with weak base

equivalence point is at 7

ether amine ester amide alkoxy

ether R-O-R' amine RNH2 (primary amine), RNHR' (secondary amine), R(NR')R'' (tertiary amine) *When an amine appears on the MCAT, think of these two reactions: 1. Nitrogen acts as a nucleophile where the lone pair ofelectrons attacks a positive charge; and 2. Nitrogen can take on a fourth bond (becoming positively charged).* ester R-(C=O)-OR amide R-(C=O)-NH2 alkoxy -OR

galvanic cell terminals electrodes anode cathode

galvanic cell: (also called a voltaic cell) offers an alternative pathway for the flow of electrons between phases. The electric potential generates a current from one phase to another in a conversion of chemical energy to electrical energy. The components of a simple galvanic cell can be represented by the letters T-E-I-E'-T', where T represents the *terminals* (conductors such as metal wires), E represents the *electrodes* (also conductors), and I represents the ionic conductor (often the salt bridge). anode: negative sign cathode: positive sign *Remember: RED CAT; AN OX: reduction at the cathode; oxidation at the anode.Remember: RED CAT; AN OX: reduction at the cathode; oxidation at the anode.* *A galvanic cell turns chemical energy into electrical energy. It's a battery,just like the one that starts your car, powers your cell phone, or energizes your flashlight. The wire between the anode and cathode is the same kind of circuit discussed in physics. Any circuit elements would appear there.* *The language and notation used to describe an electrochemical cell make sense if you consider the context of each part of the cell. The features of the anode and cathode are described in the language of chemistry- oxidation, reduction, dissolution, or precipitation of ions. The wire between them is described in the language of physics - current traveling from the + to the - (cathode to anode) and electrons moving in the opposite direction. Since the solution of an electrochemical cell is the focus of electrophoresis, you may find it described in terms of biology- the movement of negatively charged substances such as DNA toward the positively charged ions released into solution from the anode. From this perspective, the anode is assigned a +.*

zwitterion

has a positive and negative charge

relative acidity of the functional groups (strong base--> weak acid) (strong acid--> weak base)

increase acidity --> alkyl < alkene< H2 < NH3 < alkyne < aldehyde < alcohol < H2O < carboxylic acid

indicator endpoint

indicator: A chemical called an indicator can be used to find the equivalence point in a titration. The indicator is usually a weak acid whose conjugate base is a different color. endpoint: The point where the indicator changes color is called the endpoint. Do not confuse the equivalence point with the endpoint. We usually choose an indicator whose range will cover the equivalence point. *You don't need to memorize the details about how indicators work, but it's useful to understand.* *By the way, you can remember that the indicator changes color at the end- point by spelling indicator as: Endicator* *Since we established that the Henderson-Hasselvalch equation cannot ve used to find the pH of the equivalence point, how can it be used to find an indicator range that will include the equivalence point? The answer is that we are using the indicator pH concentrations in the Henderson-Hasselvalch equation, and the indicator never reaches its equivalence point in the titration. The indicator ions do not approach zero concentration near the color change range.* *If the mcat asks you which indicator to use for a titration, you should choose an indicator with a pKa as close as possible to the pH of the titration's equivalence point.*

salts

ionic compounds that dissociate in water. he dissociation of a salt often creates acidic or basic conditions. The pH of a salt solution can be predicted qualitatively by comparing the conjugates of the respective ions. The conjugate of the salt cation is the species that remains after removal of a proton. If the salt cation has no protons to donate, the conjugate is formed by the addition of OH. The conjugate of the salt anion results from the addition of a proton. If the conjugates are both strong, the salt solution is neutral. If one of the conjugates is strong and the other is weak, the pH of the salt solution favors the strong conjugate. *When considering salts, remember that all cations, except those of the alkali metals and the heavier alkaline earth metals (Ca2+, Sr2+, and Ba2_, act as weak Lewis acids) in aqueous solutions.*

ionization energy

ionization energy : energy needed to detach an electron from an atom. The second ionization energy is always greater than the first because once one electron is removed, the effective nuclear charge increases for the remaining electrons. Moving across a period to the right, increasing z .lf values pull electrons more strongly toward the nucleus. Therefore, more energy is required to rip them off *Zeff is useful for understanding all of the periodic trends. Zeff increases from left to right across a period, so each new electron is pulled closer to the nucleus and held more tightly than the previous one. Remember: 1) pulling the outermost electron closer decreases atomic radius; 2) holding the outermost electron more tightly increases ionization energy; 3) atoms with greater Zeff will pull more strongly on electrons in covalent bonds, increasing electronnegativity across a period; and 4) atoms with stronger Zeff will more readily accept another electron, so electron affinity increases across a period.*

transesterification

is just trading alkoxy groups on an ester.

ring structure formation in glucose

know the structure of glucose in this form

straight form of glucose

know the structure of glucose in this form

strong acids strong bases

know this STRONG ACIDS HI HBr HCl HNO3 HCLO4 HCL03 H2SO4 STRONG BASES NaOH KOH NH2- H- Ca(OH)2 Na2O CaO

saponification

lipid breakdown is base catalyzed in a process called saponification, soap is formed - fatty acid salts and glycerol. *If you have ever accidentally gotten a drop of a strong base on your finger in organic chemistry lab, you might have noticed it feels slippery. This is because you have made soap out of the oils in your skin. This is an example of saponification. Most soaps are now made of vegetable oils. Soap used to be made of animal fat.*

calorimeter

measures heat change The relationship between heat transfer and temperature change can be used to determine the energy change associated with a chemical or physical reaction. A device called a calorimeter A calorimeter is a container that holds a liquid, often water, with a thermometer placed inside to measure any changes in temperature. Calorimeters are useful because they are highly insulated from their surroundings. This makes them well suited to track the energy changes associated with a reaction.

formic acid acetic acid formaldehyde acetone

methanoic acid H-(C=O)-OH ethanoic acid H3C-(C=O)-OH benzoic acid Ph-(C=O)-OH formaldehyde H-(C=O)-H acetone H3C-(C=O)-CH3

molality molarity

molality= m= (moles of solute)/ (kg of solvent) molarity= M= (moles of solute)/(volume of solution

Gibbs free energy equation

must know this *On the MCAT, you may see the terms "endergonic" and "exergonic." These just mean positive deltaG (non- spontaneous) and negative deltaG (spontaneous), respectively.* *Under certain conditions delta S surrounding = -delta H system/T deltaG=0 indicates equilibrium. Negative deltaG indicates a spontaneous reaction.* *Study the Gibbs function, and, most importantly, realize that a negative delta G indicates a spontaneous reaction. Remember,the terms delta G, delta H, and delta S in the Gibbs function refer to changes in the system, not the surroundings. Also realize that since Gibbs energy is a function of enthalpy and entropy. Gibbs energy of the universe is not conserved,just as enthalpy and entropy of the universe are not conserved. The negative of the Gibbs free energy is the amount of non-PV work available in a completely reversible process, but we know that completely reversible processes are not possible in the real world. The actual amount of non-PV work that we will get out of the system is always something less than the magnitude of -deltaG.* *If a reaction produces a positive change in enthalpy and a negative change in entropy, it can never be spontaneous on its own. If a reaction produces a negative change in enthalpy and a positive change in entropy, it must be spontaneous. If the enthalpy and entropy of a reaction have the same sign, spontaneity depends on temperature. It makes sense that endothermic reactions (+deltaH) with +deltaS are spontaneous at higher temperatures, since heat transfer into the system is required. The opposite logic applies to exothermic reactions (-deltaH) with -deltaS.* endothermic graph = positive delta G exothermic graph, negative delta G

*The first quantum number is the shell. It corresponds roughly to the energy (eve( of the electrons within that shell. The second quantum number is the subshell. It gives the shape. Recognize that s orbitals are spherical and p orbitals are dumbbell-shaped. The third quantum number'is the specific orbital within a subshell. The fourth quantum number distinguishes between two electrons in the same orbital; one is spin +1/2 and the other is spin -1/2.*

n = principle quantum number -shell l = azimuthal -subshell, shape: spdf ml= magnetic -orbital = px, py, pz ms = spin -spin

nernst equation

nernst equation is the second one on the image *If Eo is positive, deltaGo is negative and K > 1. If Eo is negative, deltaGo is positive and K< 1.* *For the understand how the Nernst equation expresses the relationship between chemical concentrations and potential difference. The Nernst equation can be used to express the resting potential across the membrane of a neuron. This environment is similar to a concentration cell, discussed in the next section.*

Neutralization titration

neutralization: acid+ base --> water and salt titration: drop-by-drop mixing of an acid and a base. Titrations are usually performed for one of two reasons: 1. to find the concentration of a substance by comparing it with the known concentration of the titrant (the acid or base that is added to the substance of unknown concentration); or 2. to find the pK or pKb, and by extension the Ka or Kb, of an acid or base.

partial ionic character dipole moment Intermolecular attractions

partial ionic character: electrons are shared equally by two atoms with equivalent electronegativities, it is a nonpolar covalent bond. When the electrons are not shared equally because of a difference in electronegativity, it is a polar covalent bond. If the difference in electronegativity is significant, the bond is said to have partial ionic character. dipole moment: occurs when the center of positive charge in a bond does not coincide with the center of negative charge. The concept of center of charge is analogous to the concept of center of mass. When the center of positive charge is displaced from the center of negative charge, the bond is said to have a partial positive character on one side and a partial negative character on the other. In chemistry a dipole moment is represented by a vector pointing from the center of positive charge to the center of negative charge. Intermolecular attractions: (attractions between separate molecules) occur due to dipole moments. The partial negative charge of one molecule is attracted to the partial positive charge of another molecule. Intermolecular dipole attractions are weak electrostatic bonds

state functions

properties that describe the current state of a system internal energy (U) temperature pressure volume enthalpy entropy gibbs energy *You need to know what a state function is. State functions are pathway independent and describe the state of a system. The change in a state property going from one state to another is the same regardless of the process used to change it. Heat and work are also thermodynamic functions, but they are not state functions. If you know three macroscopic properties of a one-component system in equilibrium and at least one of them is extensive, you can find all of the other properties. Thermodynamic functions apply to systems with large numbers of molecules. They are not accurate for individual molecules or collisions. If you are asked about individual collisions, use your knowledge from physics about forces and motion.* *The MCAT may refer to internal energy as 'heat energy,' 'thermal energy,' or even 'heat.' Heat energy and thermal energy are really the vibrational, rotational, and translational parts of internal energy. They are called thermal energy because they affect temperature. Heat is a transfer of energy, and using it as another name for internal energy can create confusion. Unfortunately, this isa common mistake.*

reducing agents oxidizing agents

reducing agents -LiAlH4 -NaBH4 -H2 + pressure H-(C=O)-OC2H5 + LiALH4--> CH2OH oxidizing agents -K2Cr2O7 -K2MnO4 -H2CrO4 -O2 -PCC

saturated

saturated: as the concentration of dissolved salt increases, the rates of dissolution and precipitation equilibrate. at this point, the solution is saturated. In a saturated solution, the concentration of dissolved salt has reached a maximum. Just like the equilibrium established for a chemical reaction, the equilibrium established at the saturation point is dynamic. The overall concentrations of products and reactants do not change, but the forward and reverse reactions continue to occur at equal rates.

hybridization bond angles? shape? sp sp2 sp3 sp3d sp3d2

sp -180 -linear sp2 -120 -trigonal planar sp3 -109.5 -tetrahedral, pyramidal, bent sp3d -90, 120 -trigonal bipyramidal, seesaw, t-shaped, linear sp3d2 -90, 90 -octahedral, square pyramidal, square planar

sucrose --> maltose--> lactose--> cellulose--> amylose (starch)--> amylopectin--> glycogen-->

sucrose --> glucose + fructose alpha linkage maltose--> 2 glucose alpha linkage lactose--> galactose and glucose beta linkage cellulose--> chain of glucose molecules beta linkage amylose (starch)--> chain of glucose molecules alpha linkage amylopectin--> chain of glucose molecules alpha linkage glycogen--> chain of glucose molecules alpha linkage

enamine imine

tautomers aldehyde+ amine--> imine and enamine ketone+ amine--> imine and enamine *Notice that the tautomer of an imine is an enamine, although this can only happen when the original amine is primary. For an example of MCAT tautomers, check out the nitrogenous bases on nucleotides.*

polyprotic titration

the "midpoint" is the half equivalence point *There really isn't anything tricky about polyprotic acid titration curves. They are just made up of a series of monoprotic curves. The trickiest part is keeping in mind how many equivalents of titrant are needed to neutralize the acid.*

valence shell electron pair repulsion (VSEPR) theory

the electrons in an orbital seek to minimize their energy by moving as far away from other electron pairs as possible, minimizing the repulsive forces between them. The different types of hybridization are each associated with the formation of 120° predictable bond angles and molecular shapes

half-life *In any half-life problem, there are 4 , and only 4 , possible variables. They are: 1) the initial amount of substance, 2) the final amount of substance, 3) the length of the half-life, and 4) the number of half-lives (often given as a time period, in which case you simply divide by the length of a half-life). Any MCA"f® half-life question will provide you with three of these variables in some form, and will ask you to find the fourth. This type of question should be a fast, free point. To answer a half-life question, count the number of half-lives on your fingers. For instance, if 12.5% of a substance remains after 5 years, what is the half-life? The initial amount is, of course, 100%. The final amount is 12.5%. The number of half-lives is found by dividing the initial amount by 2 until you arrive at the final amount. Keep track on your fingers of the number of time that you divide by 2: 50 % is once , 25 % i s twice, 12.5% is three times. That's three half-lives. In another example: how long will it take for 500 grams of a substance with a half-life of 2 years to decay to 62 grams? The initial amount equals 500, the final amount equals 62, and the half-life is 2 years. Divide the initial amount by 2 until you arrive at the final amount. Keep track of the number of half-lives on your fingers. 250 is one, 125 is two, 62.5 is three. Rounding off numbers is the rule on the MCAT, so the answer is 3 half-lives or 6 years. Whatever the combination, look for the 3 variables and solve for the fourth by counting half-lives on your fingers. If you find it easier to visualize math problems as a graph, see Figure 1.27. Remember that even though we count it in half lives, radioactive decay is a continual process.* -->

the length of time necessary for one half of a given amount of a substance to decay. Radioactive decay follows first- order kinetics, and the amount of atoms that remain after decay can be expressed as follows: At=Aoe^(-kt) (exponential decay) ln(At/Ao)=-kt Ao=original amount At=amount at time t *Carbon dating uses the principles of radioactive decay to determine how old organic matter is. Radioactive isotopes are also used for some types of biomedical imaging.*

conjugate acid conjugate base

the reactants are referred to as the acid and base, and the products are called the conjugate acid and conjugate base. In every acid/ base reaction the acid has a conjugate base and the base has a conjugate acid. Deciding which form is called the conjugate simply depends on the direction in which the reaction is viewed. *It is correct to say either "HA is the conjugate acid of base A-, or "A- is the conjugate base of acid HA." The MCA"f® many ask you to identify conjugates. Remember that the stronger the acid, the weaker its conjugate base, and the stronger the base, the weaker its conjugate acid. WARNING: Many students and even some prep books translate this into "Strong acids have weak conjugate bases, and weak acids have strong conjugate bases." The second part of this statement is incorrect! Acid strength is on a logarithmic scale. A weak acid can have a strong or weak conjugate base.* *Many reactions in living cells involve the transfer of a proton. The rate of such reactions depends on the concentration of W ions, or the pH.*

Electronegativity

the tendency of an atom to attract electrons shared in a covalent bond. *Use relative electronegativity to find the polarity of a bond or a molecule. For example, in a carbonyl, a C=O bond is polar. Carbon has a partial positive charge and oxygen has a partial negative charge. This is due to oxygen's greater relative electronegativity.* *The electronegativity of hydrogen falls between that of boron and that of carbon. When bonded with hydrogen, carbon and elements to the right of carbon will carry a partial negative charge while hydrogen will carry a partial positive charge. Think of CH4 • Boron and the elements to the left of boron will carry a partial positive charge when bonded to hydrogen, while the hydrogen will carry a partial negative charge. Think of the hydrides. (H) in NaH or LiAIH3 .*

Electron affinity

the willingness of an atom to accept an additional electron. More precisely, it is the energy released when an electron is added to an isolated atom. *Some atoms have a very high affinity for electrons.* Warning: Electron affinity is sometimes described in terms of exothermicity, for which the energy released is given a negative sign. We can state this as follows: electron affinity is more exothermic to the right and up on the periodic table. The noble gases do not follow this trend. Electron affinity values for the noble gases are endothermic, because noble gases are stable and thus significant amounts of energy are required to force them to take on electrons and become less stable.

phase diagram

this is for water. the solid and liquid line for non water is more to the right *follow the energy in phase changes. It enters the substance as heat or PV work, but what happens then? During a phase change, energy breaks bonds and does NOT change the temperature. Within a given phase, energy increases molecular movement, which increases the temperature.* *Do you see why one substance can actually have many melting and boiling "points" depending on the pressure? At a fixed pressure, the temperature at which a substance melts or boils is a "point." But if we consider all possibilities (at various pressures) the temperature-at which a substance melts or vaporizes lies along a melting or boiling "curve."*

titration curve equivalence point

titration curve: starts at a very low pH; by the end of the titration, the solution is basic, so the titration curve finishes at a very high pH. For the titration of a strong base with a strong acid, the graph would start at a high pH and decrease with the addition of acid titrant. equivalence point: Notice the portion of the graph that most nearly approximates a vertical line. The midpoint of this line is called the equivalence point. The equivalence point for the titration of a monoprotic acid is the point in the titration when there are equal equivalents of acid and base in solution. (An equivalent is the amount of acid or base required to produce or consume one mole of protons.) *The Ka and therefore the pKa are intrinsic to the acid and thus are constants. The pH is environmental and thus is variable. How any species behaves is dependent on the environment. When the pH is lower than the pKa, a species interprets the environment as protic (full of H+ ions) and it is less likely to act acidic. When the pH is greater than the pK3 , a species interprets the environment as aprotic (few H+ ions) and it is more likely to act acidic. Some molecules can act as an acid in one environment, and a base in another.* *A monoprotic acid is simply an acid with only one hydrogen that can be lost. HCI and CH3 COOH are monoprotic, but H2S04 and H3P04 are not.*

isoelectric point

with all diprotic acids, there will be two equivalence points - one for each equivalent of added base. However, the first equivalence point is unique. At this point, the carboxylic acid group has been fully deprotonated and nearly all of the amino acid exists in the zwitterionic form. Because there is one positive and one negative charge, this species of the amino acid is neutral. The pH at which this occurs is called the isoelectric point pl. *Uncharged amino acids are non- acidic and non-basic. Recall from the Biological Molecules and Enzymes Lecture that the basic amino acids are arginine, lysine, and histidine, while the acidic amino acids are aspartic acid and glutamic acid. Cysteine and tyrosine side chains can also act as acids at high pH . The remaining 13 common amino acids have pi values near 6 .* *Proteins can be separated in a gel based on their isoelectric points. Proteins are chains of many amino acids. Combining the isoelectric points of the individual amino acids gives a protein its pl. Since the -COOH group and the -NH2 group are joined in a peptide bond, they are not acidic or basic within the protein. This means that the side chains of the charged amino acids determine the pi of the protein.*