Bootcamp chem test bank Ch 1-8

Below is the unbalanced chemical equation for the combustion of C2H2. From left to right, what are the coefficients in the balanced chemical equation? __C2H2 + ___ O2 --> ____ CO2 + ____ H20

2,5,4,2

Aspirin, shown below, is used to treat pain, fever, and inflammation. How many sigma (σ) and pi (π) bonds are present in a molecule of aspirin?

21 sigma and 5 pie Single bonds are made of sigma bonds. Double bonds are made of one sigma bond and one pi bond; triple bonds are made of one sigma bond and two pi bonds. So for aspirin, we count all the single bonds (which each contain one sigma bond) and all of the double bonds (which each contain one sigma bond), for a total of 21 sigma bonds. Each of the double bonds contains one pi bond, which gives us a total of 5 pi bonds.

Which of the following aqueous solutions has approximately the same boiling point as that of a 0.15 m NaCl solution? a. 0.1 m MgCl2 b. 0.2 m ethylene glycol c. 0.15 m glucose d. 0.15 m Na2S e. 0.2 m AlCl3

A

The solubility of BaSO4 in water is 2 mg/L at 25 oC. A 2 mg BaSO4 sample was added to 100 mL water. Some of the solid dissolved while 1.8 mg of it remained as precipitate. The solution is said to be . a. saturated b. supersaturated c. unsaturated d. dilute e. pure

A A saturated solution is one that contains the maximum amount of solute that a solvent can dissolve. In such a solution, the rate of dissolution is equal to the rate of crystallization. If the amount of solute dissolved is greater than the solubility, then we have a supersaturated solution. On the other hand, if the solute dissolved is less than the solubility, then an unsaturated solution is formed.

The compound formed between an unknown metallic element, M, and chlorine has a formula MCl2. What is the formula of the compound formed between M and oxygen?

A metal reacts with a nonmetal to form an ionic compound. If M reacts with Cl2 to form MCl2, this means that M forms a stable +2 ion (M2+) since chlorine forms Cl- (there are two Cl atoms in MCl2). When M reacts with oxygen, the product formed would have the formula MO since oxygen forms O2- and we've determined that M is M2+.

A sample of an ideal gas at 298K and 3 atm has a volume of 2.5 L. What will be the volume of the same sample of gas at 1 atm pressure and 298K?

At constant temperature and amount of gas, pressure is inversely proportional to volume. If pressure decreases to 1/3 its initial amount (3 atm → 1 atm), the volume will increase by 3 times. Therefore, the new volume will be 7.5 L.

Two ideal gases, X and Y, are at the same temperature and have the same number of molecules. The pressure of gas X is twice that of gas Y. The volume of gas X will be .

At constant temperature and number of moles (moles is a representation of number of molecules), the pressure, P of an ideal gas is inversely proportional to its volume, V (Boyle's Law): Thus, in order for X to have a pressure twice that of Y, its volume must be one-half that of Y.

A flask contains 5.5 mol of O2 gas at 25 oC and 2.00 atm. How much O2 gas, in moles, must be added to increase the pressure to 8.00 atm at constant temperature and volume?

At constant temperature and volume, the pressure of a gas is directly proportional to the number of moles of gas. Increasing the pressure from 2.00 atm to 8.00 atm requires an increase in the number of moles of O2 from 5.5 mol to 22 mol, or an additional 16.5 mol of O.

All of the following statements regarding catalysts are true EXCEPT one. Which one is the EXCEPTION? a. catalysts are regenerated at the end of a reaction b. catalysts directly lower the activation energy of a reaction c. performing a reaction with a catalyst speeds it up d. the equilibirum of a reaxtion is not shifted w the addition of a catalyst e. many biological processes depend on catalysts

B

Consider a solution that contains 0.1 mol of benzene and 0.2 mol of toluene. What is the vapor pressure of this solution at 25 oC? The vapor pressure of pure benzene and pure toluene is 75 torr and 21 torr, respectively. a. 12 torr b. 39 torr c. 48 torr d. 54 torr e. 96 torr

B

In which of the following solvents is carbon tetrachloride, CCl4, most soluble, and what intermolecular force between solute and solvent is the most important? a. water, H bonding b. hexane, dispersion (C6H14) c. acetone, dispersion (CH3C(O)CH3) d. ethanol, dipole dipole (C2H5OH) e. chloroform, dispersion (CHCl3)

B The solubility of a solute in a solvent is determined by the relative strength of attractive forces between solute-solute, solvent-solvent, and solute-solvent. A solute is more soluble in a solvent with similar intermolecular forces to its own (like dissolves like). Carbon tetrachloride is nonpolar and its molecules are held by dispersion forces. So we expect it to dissolve through dispersion forces. All other solvents given, except hexane, have polar groups. The nonpolar CCl4 will interact weakly with these polar solvents.

Which of the following statements is true regarding a first order reaction? a. the half life of a first order reaction increases with increasing initial concentration of the reactant b. the half life is dependent of the initial concentration of the reacntnt. c. the half life is independent of the intiial concentration of the reactant d. the rate constant of a first order reaction increases w time e. the rate of a first order reaction increases w time

C

Which one of the following is most likely to dissolve in toluene, C7H8? a. HBr b. NACl c. C6H14 d. CH3CN e. CHCl3

C A substance is expected to dissolve in a solvent if the strength of their intermolecular forces are similar. Toluene, like other hydrocarbons, is nonpolar and is held by dispersion forces. Other nonpolar substances, such as C6H14, are thus expected to dissolve in toluene. HBr, CH3CN and CHCl3 are polar substances and are held by dipole-dipole forces, and NaCl are held by ionic bonds.

Why is methanol more soluble in water than isopentyl alcohol (which is also known as isoamyl alcohol)? a. methanol has less steric hindrance b. water can more directly solvate methanol c. methanol has fewer hydrocarbons d. branched alkanes aggregate to form precipitates e. none of hte above

C Alcohols, having an -OH group, are capable of hydrogen bonding with water, facilitating their solubility in water. Their hydrocarbon portions are nonpolar thereby decreasing their solubility. Thus, the solubility of alcohols decreases as we add more hydrocarbons.

All of the following would triple the osmotic pressure EXCEPT one. Which one is the EXCEPTION? a. increasing the temperature from 298 K to 894 K b. changing the solute from 0.2 M acetic acid to 0.2 M CaCl2 c. changing the solute from 0.2 M NaCl to 0.6 M Na3PO4 d. tripling the amount of NaCl solute in a solution

C Osmotic pressure is the pressure that must be applied to prevent net movement of water from lower concentration to higher concentration. The osmotic pressure, Π, of a solution is given by pi=iMRT where i is the van't Hoff factor, M is the molarity of the solution, R is the ideal gas constant, and T is the absolute temperature. The van't Hoff factor is determined by the number of particles that the solute dissociates into in solution (i = 1 for nonelectrolyte). Tripling the temperature (A), tripling the van't Hoff factor (B), or tripling the molarity (D) would triple the osmotic pressure. In C), we double the van't Hoff factor and also triple the molarity, which would result in six times the osmotic pressure.

Consider this reaction: C(s) + CO2(g) → 2 CO(g) This is a first order reaction with respect to CO2 and zero order with respect to C. The following diagram depicts a reaction mixture in a sealed container as a function of time. What is the half-life of the reaction? a. 20 min b. 25 c. 50 d. 100 e. 200

C The half-life of a reaction is the time it takes for the concentration of a reactant to reach half its initial value. We can count the molecules in each mixture and determine at what point does the amount of CO2 reach half its original concentration. In A, we start with 8 CO2 molecules. In B, we have 6 CO2 and 4 CO, which means that only 2 CO2 has reacted after 20 min. In C, we have 4 CO2 and 8 CO; half of the initial CO2 has been reacted. Thus, the half-life of the reaction is 50 min.

Of the following aqueous solutions, has the lowest freezing point. a. 0.2 m acetic acid b. 0.2 m sucrose c. 0.2 m NaCl d. 0.2 m NH4OH e. all freeze the same

C The freezing point of solvent is decreased when added with a nonvolatile solute. This is due to a fact the the vapor pressure of the solution is always less than that of the solvent. The freezing point depression. DTf, can be expressed mathematically as T=imK We are given four solutions with the same concentration. We now compare the van't Hoff factors for each solute. Sucrose is a nonelectrolyte, i.e. it does not dissociate into ions in solution, so its i = 1. Acetic acid, NaCl, and NH4OH all dissociates into ions in solution. Acetic acid and NH4OH are weak electrolytes, they are only partially dissociated into ions in solution. NaCl on the other hand is a strong electrolyte, i.e. it completely dissociates into ions in solution. So NaCl has the highest i value and thus the lowest freezing point.

Which of the following molecules has a nonzero net dipole moment? a. CH3Cl b. CH4 c. CF4 d. CH3CH2CH3 e. BF3

CH3Cl A polar molecule has a nonzero net dipole moment. The types of bonds and shape of the molecule determine net dipole moment. For a molecule to be polar, it must have a polar bond and the polarity of the bonds must not cancel. In [A], the molecule is tetrahedral and the C-Cl bond is polar and since there is only one C-Cl bond, this molecule is expected to be polar. Molecule B is nonpolar (all hydrocarbons are nonpolar0. The bonds in [C] are polar (C-F) but overall the molecule is nonpolar since it is symmetrical and the bond polarity cancels out. [D] is a hydrocarbon and therefore is nonpolar. The bonds in [E] are polar (B-F) but the molecule is trigonal planar and symmetrical so the bond polarity cancels, making the molecule nonpolar.

Consider the following reaction: 2 A + B → 3 C What is the rate of formation of C at an instant when A is reacting at a rate of 0.60 M/s? a. .1 M/s b. .2 c. .4 d. .9 e. 1.8

D

Which of the following statements is false? a. a decrease in temperature cases a decrease in reaction rate b. a increase in Ea causes a decrease in k c. temperature and collision frequency have a direct relationship d. a reactions kinetic energy influences its Ea e. reaction speed and Ea have an indirect relationship

D

Chloroform and dichloromethane boil at 60 °C and 40 °C, respectively. Equimolar amounts of chloroform and dichloromethane were mixed. The resulting solution will boil . a. above 60 deg C b. below 40 c. at 60 d. at 50 e. at 40

D From Raoult's law, the vapor pressure of a solution of two volatile liquids will be between the vapor pressure of the pure liquids, and this is given mathematically as Psolution=XaPa+Xb+Pb where Psolution is the vapor pressure of the solution, Xa and Xb are the mole fractions of A and B, respectively, and Pa and Pb are the vapor pressure of pure A and pure B, respectively. Boiling point is defined as the temperature at which the vapor pressure equals the atmospheric pressure. Since the vapor pressure of the solution is somewhere in between the vapor pressure of the pure liquids, then we expect the boiling point of the solution to be in between the boiling points of the pure liquids. If equimolar amounts were not mixed (ie. more of one of the solutions) the boiling point of the solution will be closer to the boiling point of the component with the higher mole fraction.

A concentrated solution of nitric acid contains 90% HNO3 by mass and has a density of 1.50 g/mL. Which of the following statements is true? a. 1 ml of this solution contains 1.5 g of HNO3 b. 100 g of this solution contains 150 g of HNO3 c. 1 L of this solution contains 90 g of HNO3 d. 100 g of this solution contains 90 g of HNO3 e. 1.5 mL of this solution contains 90 g of HNO3

D The percent by mass of a solution is the mass of solute dissolved in 100 g of solution (mass of solute + mass of solvent). percent mass= g solute/g solution * 100 Thus, a 90% HNO3 mass means that there are 90 g of HNO3 dissolved per 100 g of solution. The density of a solution is the mass of solution per mL of solution. A 1.50 g/mL solution means the solution weighs 1.50 g for every mL of solution.

Determine the vapor pressure of a solution of chloroform and dichloromethane, where the mole fraction of chloroform is 0.40. The vapor pressure of chloroform is 160 mmHg, while that of dichloromethane is 540 mmHg. a. 160 mm Hg b. 350 mmHg c. 380 mmHg d. 388 mmHg e. 540 mmHg

D We are given the vapor pressure of chloroform and dichloromethane. The mole fraction of chloroform in solution is given as 0.40, which means that the mole fraction of dichloromethane is 0.60. Substituting these into the equation above gives

Which of the following substances exhibits a dipole-dipole attractive force between its molecules? I. Br2 II. CH2Cl2 III. CH3CN

Dipole-dipole intermolecular forces are found in molecules that are polar (net nonzero dipole moment). Bromine, Br2, is a nonpolar molecule so it does not exhibit dipole-dipole. Dichloromethane, CH2Cl2, and acetonitrile, CH3CN, both have polar groups and are polar. These two substances are held together by dipole-dipole intermolecular forces.

What is a possible rate law of this overall reaction? A + B --> C+D a. rate = k [A][B] b. rate = l[a][b]/[c][d] c. rate = k=[a][b]^2 d. rate = l[c][d] e. more than one

E both a and c

Consider a substance that has a triple point of 1.5 atm and 250 K and a critical point of 10 atm and 700 K. Its solid-liquid line has a positive slope (leans to the right). At which of the following pressures and temperatures will the substance exist as a solid? a. 1 atom and 250 K b. 2 atm and 250 K c. 1.5 atm and 300 K d. 3 atm and 500 K e. .5 atm and 600 K

From the given information, we can sketch the following phase diagram: From the given pressures and temperatures, we can see that only B is where the substance exists as a solid.

The plot below depicts the solubility of solid X in water as a function of temperature. A 3-g sample of X was added to 100 mL of water at 25 oC. Which of the following statements is true? a. a supersaturated solution of x is formed b. the 3 g sample of x will dissolve completely at 25 degree c c. some x will dissolve and heating the resulting solution to 40 degree c, avoiding loss of solvent through evaporation, would result in complete dissolution of x d. an unsaturated solution of x is formed e. all 2g of x will not dissolve

From the plot, we see that the solubility of X at 25 oC is 20 g/L or 2 g/100 mL. If we add 3 g of X into 100 mL of water, only 2 g of it will dissolve, forming a saturated solution of X. Increasing the temperature increases the solubility of X. At 40 oC, its solubility is 35 g/L or 3.5 g/100 mL. Heating the resulting solution to 40 oC should result to complete dissolution of X. C

What is the correct definition of Hund's Rule?

Hund's Rule states that every orbital in a certain subshell (s, p, d or f) must be occupied by a single electron before any one orbital can have two electrons.

Molecules of which of the following compounds would have intermolecular hydrogen bonding to other molecules of the same types? I. CH3CH2OH II. CH3OCH3 III. CH3COCH3 IV. CH3COH

Hydrogen bonding is exhibited by molecules that contain an H atom covalently bonded to highly electronegative atoms F, N, or O. The H has to be bonded to one of these atoms directly. Although all the molecules given have O and H in their formula, only molecule A has an H that is bonded to an O and therefore exhibits hydrogen bonding.

Which of the following are conditions necessary for a reaction to occur according to the collision theory? I. Molecules must collide II. Molecules must collide with the same energy III. Molecules must collide with a specific 3-D orientation

I and III

Which of the following atoms has the electron configuration [Ar]4s23d2? I. Ti II. Mn3+ III. Sc2-

I only The given electron configuration is ground-state Ti's electron configuration, so we know Ti must be one of the correct answers. The ground-state electron configuration of Mn is [Ar]4s23d5; to find the configuration of Mn3+, we simply remove 3 electrons starting with the highest energy orbital. Recall that the 4s orbital is the highest energy orbital available in Mn, so we remove both electrons from the 4s orbital, then remove a third electron from the 3d orbitals to end up with [Ar]3d4 as the electron configuration of Mn3+. Sc's ground-state electron configuration is [Ar]4s23d1. To find the configuration of Sc2-, we simply add 2 electrons to the lowest energy orbital available (in this case, the 3d orbital), giving us [Ar]4s23d3. *Note: This is an important rule to keep in mind with this question: 3d is actually at a higher energy level than 4s until the orbitals are filled. Once filled, 4s is higher than 3d.

Consider two gases: 1.0 mol of He in a 1.0 L container at 25 oC 2.0 mol of Ne in a 1.0 L container at 25 oC. Which of the following statements is true regarding these two gases? Assume both gases obey ideal gas behaviors. I. Molecules of He travel faster than molecules of Ne. II. The gas molecules of Ne have a higher average kinetic energy than those of He. III. The two gases have the same pressure.

I only We can calculate the molar mass of the unknown gas using the given density in order to identify it. The molar mass of a gas is related to its density via the equation: ρ=PM/RT where ρ is the density, P is the pressure of the gas, M is the molar mass of the gas, R is the ideal gas constant, and T is the absolute temperature. Substituting the given values and solving for M: The molar mass of the unknown gas is approximately 72 g/mol, and the gas that has the closest molar mass is Cl2 (70.9 g/mol)

Which of the following is polar? I. CH4 II. H2S III. BH3 IV. NH3

II and IV only Polar molecules are those that have nonzero dipole moments. These are molecules that contain polar bonds (bonds between atoms of different electronegativities) and are asymmetrical. In order to determine the polarity of molecules, we have to know its Lewis structure and geometry, and assess the bond polarity based on the structure. CH4 is tetrahedral, which is symmetrical, and its bonds (C-H) are considered nonpolar. Therefore, CH4 is nonpolar. H2S is bent, and the two H-S bonds are polar. A great comparison to this molecule is H2O, which we know is polar. Like water, the molecule is asymmetrical, as its dipole moments do not cancel equally. Therefore, it is polar. The shape of BH3 is trigonal planar. The molecule is symmetrical, with all three bond equivalent. Therefore, it is nonpolar. The N-H bonds on NH3 are polar and the molecule is asymmetrical (trigonal pyramidal in shape). Therefore, NH3 is polar.

Arrange the following in increasing order of the indicated bond angle. I. H-P-H in PH3 II. H-S-H in H2S III. H-Si-H in SiH4

II<I<III All three molecules contain four electron pairs (bonding pairs + lone pairs) around the central atoms. For SiH4, which contains all four bonding pairs, the bond angle is 109.5° (tetrahedral shape). In PH3, stronger repulsion by the lone pair make the H-P-H bond angle less than the ideal 109.5° angle. The lone pair on PH3 forces the P-H bonding pairs closer to each other, resulting in a smaller bond angle. The bond angle in H2S is much smaller, since the repulsion from two lone pairs is greater than from one.

Rank the following aqueous solutions in order of increasing boiling point. I. 0.20 M CaCl2 II. 0.30 M sucrose III. 0.40 M NaCl

II<I<III The boiling point of a solvent is increased in the presence of a nonvolatile solute. The increase in boiling point is determined by the product of the concentration, C and the number of particles in solution, i. When CaCl2 dissolves in water, it dissociates into 1 Ca2+ and 2 Cl- ions per formula unit. Similarly, NaCl dissociates into 1 Na+ and 1 Cl- ion. On the other hand, sucrose does not dissociate into ions when dissolved in water. Considering both concentration and number of particles in solution, a 0.40 M NaCl will have the highest boiling point (0.40 M x 2 particles = 0.80) while sucrose will have the lowest boiling point (0.30 M x 1 particle = 0.30).

Which of the following compounds has the largest % composition (by mass) of carbon? I. CO2 II. C6H12O6 III. C3H8

III

The following diagram depicts three different mixtures containing He, Ne, and Ar gas. Rank them in order of increasing mole fraction of He.

III<I<II We are given three mixtures containing different amounts of gases. We count the number of atoms of He gas and the total number of atoms of gas in each mixture and use the equation for the mole fraction, X X= number of mole of a component/total mole in the mixture For I, there are 3 He and 9 total gas molecules, so the mole fraction of He is 3/9 = 1/3. For II, 2 He and 4 total gas molecules are in the mixture, so the mole fraction of He is 2/4 = ½ For III, there are 2 He and 8 total gas molecules, so He has a mole fraction of 2/8 = 1/4

Arrange the following diatomic species in order of increasing bond strength: I. O2 II. N2 III. F2

III<I<II Bond strength increases with increasing number of bonds: triple bonds are stronger than double bonds, which in turn are stronger than single bonds. The bond in O2 is a double bond: O=O, in N2 a triple bond, N≡N, and in F2 a single bond, F-F. Therefore, F2 has the weakest bond and N2 has the strongest.

Which of the following is the ground-state electron configuration of Mo?

Mo is one of the five exceptions to typical electron configuration highlighted in Dr. Mike's Videos; the others are Cr, Cu, Ag, and Au. Each of these elements removes one of the electrons from its outermost s-orbital and places in its outermost d-orbital. Doing this allows Cr and Mo to half-fill their d-orbitals as well as have all of their valence electrons unpaired, which is more favorable than having some of them paired (as described by Hund's Rule). Cu, Ag and Au do this because it enables them to completely fill their d-orbitals. When the d-orbitals are filled, they drop in energy below their corresponding s-orbital, making them a more favorable destination for electrons than the higher energy s-orbital according to the Aufbau principle. [Kr]5s14d5

Molecules of acetone (shown below) exhibit which intermolecular force(s)? I. dipole-dipole II. London dispersion III. Hydrogen bonding

Polar molecules exhibit dipole-dipole intermolecular forces. London dispersion forces are present in all molecules and are thus the only intermolecular force in nonpolar molecules. Hydrogen bonding is a special case of dipole-dipole and is found in molecules that have an H atom covalently bonded to O, N, or F atom. We do not have hydrogen bonding in this molecule. Acetone is a polar molecule (due to polar C=O bond), so the intermolecular forces present in acetone are London dispersion and dipole-dipole.

What is the maximum number of electrons that can be placed in the d-orbitals of a singular energy level?

Recall that each individual orbital, regardless of its energy level, can hold up to two electrons. Also recall that there are five unique d-orbitals, each capable of holding up to two electrons, per energy level. Thus, the maximum number of electrons that can be placed inside the d-orbitals of a singular energy level is 5 x 2 = 10.

Which of the following statements is true regarding the vapor pressure of a liquid? I. Vapor pressure of a liquid increases with increasing temperature. II. Liquids that have higher vapor pressure boil at a lower temperature. III. Liquids that have high vapor pressure are volatile.

Statement I is correct. Increasing the temperature increases the average kinetic energy of molecules, allowing more molecules to escape the liquid phase and go to the gas phase increasing the vapor pressure. The boiling point is the temperature at which the vapor pressure equals the external pressure. The higher the vapor pressure of a liquid, the less energy it requires to increase its vapor pressure to the external pressure. Thus, the liquid will have a relatively lower boiling point. Liquids with high vapor pressure boil at a lower temperature. Thus, they are said to be volatile (boil easily).

Arrange the following in order of increasing C-O bond strength. I. CO2 II. CO32- III. CO

The Lewis structures of the three species given is shown below: Double bonds are stronger than single bonds, and triple bonds are stronger than double bonds. The C-O bond in CO32- is the weakest. This is followed by CO2, which has a C=O bond. CO has the strongest C-O bond, since it's a triple bond. II<I<III

Rank the following liquids in order of increasing boiling point. I. Butane, CH3CH2CH2CH3 (58 g/mol) II. n-propanol, CH3CH2CH2OH (60 g/mol) III. acetone, (58 g/mol)

The boiling point depends on the strength of the attractive forces in each substance. We need to assess the intermolecular force of attraction for each substance. Molecules of butane experience the weakest attractive force, London dispersion. London dispersion is present in all molecules and is the only attractive force in nonpolar molecules. So butane has the lowest boiling point. Molecules of n-propanol exhibit London dispersion and H-bonding. H-bonding is a strong type of intermolecular attractive force. So, n-propanol has the highest boiling point. Acetone is a polar molecule. Thus, its molecules exhibit London dispersion and dipole-dipole. It has a boiling point between butane and n-propanol.

Which of the following is true of paramagnetic substances? I. They always have odd numbers of electrons, never even II. They have unpaired electrons III. They are repelled slightly by a magnet

The definition of a paramagnetic substance is an substance that has unpaired electrons, making answer II correct. If an atom has an odd number of electrons, it will always be paramagnetic; however, some atoms with an even number of electrons are also paramagnetic, making I false. Lastly, paramagnetic substances are attracted to magnets, not repelled by them, so III is also false.

Arrange the following gases in order of increasing density at STP, assuming ideal behavior. I. Methane, CH4 II. Fluorine, F2 III. Carbon Dioxide, CO2

The density of an ideal gas is given by the equation density=PM/RT where P is the pressure, M is the molar mass, R is the ideal gas constant, and T is the temperature. At constant pressure and temperature, the larger the molar mass of a gas, the higher its density will be. Therefore, methane has the lowest density as it has the lowest M, while carbon dioxide has the highest density as the highest M.

In which orbital would you expect to find an electron with the following set of quantum numbers? n=4, l=3, ml=1, ms= -1/2

The first quantum number, n, known as the principal quantum number, indicates the energy level of the electron. In this case, the electron is in the 4th valence shell, as n=4. The second quantum number, l, known as the azimuthal number, tells us what kind of orbital (s, p, d or f) the electron is in, according to the following chart: s: When l = 0 p: When l = 1 d: When l = 2 f: When l = 3 Since in this question n=4 and l=3, the answer must be 4f. The last two values, ml and ms, tell us which specific f orbital the electron is in and what its spin is. The specificity of these last two values is beyond that required to get the correct answer for this question, so we ignore them.

How many protons, neutrons, and electrons does the 55Fe2+ ion have, respectively?

The number of protons in an element never changes, as that is what makes each element unique. If the number of protons in an element changes, then the element itself changes. Looking at the periodic table, we see that Fe has 26 protons, so we can eliminate any answer choices where 26 is not the first number given ([C] and [D]). We can find the number of neutrons by remembering that the 55 superscript is the mass number of our ion; the mass number is equal to [the number of protons in the ion] + [the number of neutrons]. Thus, we write: 55 = 26 + # of neutrons 55 - 26 = # of neutrons 29 = # of neutrons Lastly, we recall that neutral atoms have an equal number of protons and electrons. We add or remove electrons to give negative or positive charges to ions, respectively. Because our ion has a charge of 2+, we must have two more protons than electrons. Thus, we must have 24 electrons. Note: A simple expression that can be used to find the number of electrons an atom possesses is electrons = protons - charge of atom.

A mixture of He and Ne gases exerts a total pressure of 1.50 atm. If the mole fraction of He in the mixture is 0.40, what is the partial pressure of Ne?

The partial pressure of a gas in a mixture is also equal to the mole fraction of that gas times the total pressure of the mixture. Given that the mole fraction of He is 0.40, and that the only other gas in the mixture is Ne, it follows that the mole fraction of Ne is 0.60 (the mole fraction of all the components in a mixture adds up to 1). Therefore, the partial pressure of Ne is 0.60 * 1.50 atm = 0.90 atm.

A certain solar panel has a work function equal to 2.5 eV. If you want the energy of expelled electrons to equal 6 eV, what energy photons must strike the solar panel?

The photoelectric effect states that we can eject electrons from substances by hitting those electrons with a photon of sufficient energy. The photon has to have enough energy to knock the electron free; this energy is known as the work function of the electron. We can calculate the energy of an ejected electron as follows: Eejected = Ephoton - Φ Where Φ is the work function of the electron. Here we are asked to calculate the Ephoton required to have Eejected equal 6 eV given that Φ = 2.5 eV. We rewrite the equation to solve for Ephoton: Eejected + Φ = Ephoton 6 + 2.5 = Ephoton

A → B + C For the reaction above, the concentration of A was monitored as a function of time and the following plots were generated. What is the rate law and the value of the rate constant for this reaction? The equation below each graph is the equation of the best fit line A. rate = k[A], k=.01 s-1 B. rate = k[A]2, k=.161 M-1 s-1 C. rate = k, k=1.79e-3 M-1 s-1 D. rate = k[A], k=1.84e-8 s-1 E. rate = k, k=.642 s-1

The plot of ln [A] vs. time is linear for a first order reaction. For second order reaction, 1/[A] vs. time is linear. For a zero order reaction, [A] varies linearly with time. The rate constant is the absolute value of the slope of the best fit line of the graph. Since the given graph of ln [A] vs. time is linear, then the reaction is first order with respect to A. The equation of a line of best fit is y=mx+b, with m representing the slope. We see in our data that y = -0.01x - 1.84 x 10-8 The absolute value of the slope tells us our rate constant = 0.01. A

The reaction 2 A + B → A2B is zero order with respect to A and second order with respect to B. Doubling the concentration of A and increasing the concentration of B by a factor of three would . a. double the rate b. increase the rate by a factor of 6 . c. decrease the rate by half d. decrease the rate by 1.6 e. increase the rate by 9

The rate law for the reaction can be written as Rate = k[A]0[B]2= k[B]2 Thus, doubling the concentration of A will not affect the rate, while increasing the concentration of B by a factor of three will increase the rate by a factor of nine. Ratenew = k[3B]2 Ratenew = 9 * Rateold E

Consider this reaction: 2 NO(g) + O2(g) → 2 NO2(g) Suppose equimolar amounts of NO and O2 were placed in a sealed container and allowed to react. Which of the following statements regarding the reaction is correct? I. The rate of the reaction increases as the reaction progresses. II. Decreasing the volume of the container increases the rate. III. The rate constant increases with time.

The rate of a chemical reaction depends on the concentration of reactants. As the reaction progresses, reactants are converted into products, so their concentration decreases. Therefore, the rate decreases with time. Decreasing the volume of the container increases the pressure of gaseous reactants (pressure and volume are inversely related), thereby increasing the reaction rate. The rate constant does not change with time. Only by changing the temperature does the value of the rate constant change. II only

Which two of the following gases will exhibit approximately the same rate of diffusion? I. Ethylene, C2H4 II. Ethane, C2H6 III. Carbon Monoxide, CO IV. Carbon Dioxide, CO2

The rate of diffusion of a gas is inversely proportional to its molecular weight: lighter molecules travel faster than heavier ones

Which of the following molecules is/are polar? I. BH3 II. CH3 III. NH3 IV. H2O

The shape and the type of bonds in a molecule determine polarity. Polar molecules have a nonzero dipole moment, and are those that contain polar bonds and have an asymmetrical shape. Lewis structures will help us assess the polarity of molecules. BH3 has polar B-H bonds but the bond dipoles cancel out so the molecule is nonpolar. CH4 is basically nonpolar. C-H bonds are considered nonpolar. Hydrocarbons (those that contains C's and H's only) are nonpolar molecules. NH3 has a polar N-H bond. It has a trigonal pyramidal geometry. Therefore, it is polar. H2O has polar O-H bonds, and has a bent or V-shape geometry. It is polar.

Arrange the following substances in order of decreasing strength of intermolecular forces of attraction: a. Ar b. CH3CH2OH c. CH2Cl2

The strength of intermolecular forces of attraction follows the trend: H-bond > dipole-dipole > dispersion. Ethanol, CH3CH2OH, has an H bonded to O, so it can hydrogen-bond. Dichloromethane, CH2Cl2, is polar and therefore has dipole-dipole. Argon is nonpolar and only has dispersion.

The electrons in the 2p orbitals of which of the following is closest to the nucleus? Al, Si, P or S

The three atoms are in period 3 of the periodic table. The electrons in S experience greater attraction towards the nucleus since it has the greatest number of protons, and the same number of inner shell electrons. Thus, its electrons will be closest to the nucleus. This is the reason why atomic size decreases from left to right across a period, due to an increase in the effective nuclear charge.

The reaction NO2 (g) + CO (g) → NO (g) + CO2 (g) has a rate law that is second order overall. What are the units of the rate constant? a. m s-1 b. m-1 s-1 c. s-1 d. m s e. m-2 s-1

The units for rate is M/s, and the unit for concentration is M. The rate law for the reaction can be written as Rate = k[reactant]2 Now let's substitute in our units M/s = k[M]2 M/s = kM2 Therefore, in order to have the units we require so that the rate will have units M/s, the rate constant must have units of M-1 s-1. When M-1 s-1 is multiplied by M2 on the right hand side of the equation, we end up with M/s on the left side of the equation. B

The central atom of a molecule has 3 bonding pairs and 1 lone pair. What is the molecular geometry of the molecule?

The valence shell electron pair repulsion theory predicts the geometry (shape) of molecules. It is based on the idea that atoms in a molecule arrange themselves so as to minimize electronic repulsions. In this case, the molecule resists repulsion from its lone electrons, which take up more space than bonded electrons, by compressing its bonding electrons closer together, forming a trigonal pyramidal shape. A molecule with a central atom having 3 bonding pairs and 1 lone pair adopts a trigonal pyramid shape:

Arrange the following in order of increasing vapor pressure at 25 oC. I. Butane, CH3CH2CH2CH3 II. Ethanol, CH3CH2OH III. Dimethyl ether, CH3OCH3

The vapor pressure is dependent on the strength of intermolecular forces in each liquid. At a given temperature, the weaker the intermolecular force in the liquid, the higher its vapor pressure. Butane exhibits London dispersion between molecules, which is the weakest type of intermolecular force. So, butane should have the highest vapor pressure. Ethanol molecules are held together by strong hydrogen bonding so it has the lowest vapor pressure. Dimethyl ether has dipole-dipole interactions as a result of the difference in the electronegativity of its C and O atoms. Dipole-dipole interactions are weaker than hydrogen bonds, but stronger than London dispersion forces. Thus, the vapor pressure of dimethyl ether will be between ethanol and butane.

Statement I is correct. Increasing the temperature increases the average kinetic energy of molecules, allowing more molecules to escape the liquid phase and go to the gas phase increasing the vapor pressure. The boiling point is the temperature at which the vapor pressure equals the external pressure. The higher the vapor pressure of a liquid, the less energy it requires to increase its vapor pressure to the external pressure. Thus, the liquid will have a relatively lower boiling point. Liquids with high vapor pressure boil at a lower temperature. Thus, they are said to be volatile (boil easily).

The vapor pressure of a liquid is a measure of the amount of vapor that can exist above the liquid. The higher the vapor pressure, the easier it is to boil the liquid (lower boiling point) and the more volatile the liquid is (it evaporates easily). Thus, choice B is incorrect and choice D is correct. A solution containing two liquids will have a vapor pressure intermediate of the vapor pressure of the pure liquids and will have a boiling point between that of the pure liquids. The more volatile component (higher vapor pressure) will be relatively richer in the vapor.

The central atom of the most stable Lewis structure of SCl2 has bonding pairs (bp) and lone pairs (lp).

There are 20 valence electrons in SCl2 (6 from S, 7 from each of the Cl). The S atom is the central atom, with two Cl bonded to it. We put 8 electrons on each of the Cl (two of which are bonding electrons) as shown: Now, we have placed 16 total electrons, which means that we still have 4 more electrons to add into the structure for a total of 20 valence electrons. We place these 4 electrons as lone pairs on S: 2 bp and 2 lp

Which of the following electron transitions would produce an emission of light with the shortest wavelength? a. n=1 to n=2 b. n=4 to n=5 c. n=3 to n=5 d. n=2 to n=1 e. n=5 to n=4

This question is testing a few different concepts at once. Let's review the necessary information to correctly answer this question. First, recall that photons are only emitted from an atom when electrons fall in energy level. For example, going from 2 to 1 would lead to an emission of light, but going from 1 to 2 would require an absorption of light. Second, realize that the differences between different energy levels (n) decreases as you increase in energy levels. In other words, the difference between energy levels 1 and 2 is larger than the difference between energy levels 4 and 5. Lastly, remember that as the wavelength of a photon decreases, the energy of that photon increases. In other words, this question wants us to select the energy change corresponding to the release of the highest energy photon. n=2 to n=1

What is the electron configuration of Si?

We always fill orbitals starting with the lowest energy, 1s orbital. We put two electrons in each orbital before moving to the next orbital type. Because Si is in the 3rd row of the periodic table and it is in the p-block, we would assume that Si's electron configuration should end with 3px. We also know that neutral Si should have 14 electrons, as it has 14 protons. Let's list the orbitals from lowest to highest energy until we hit the 3p orbitals: 1s, 2s, 2p, 3s, 3p Now, beginning with the 1s orbital, let's put two electrons in each s level and six in each p level (2 for each of the 3 p orbitals) until we hit 14 electrons total. 1s22s22p63s2 At this point we have placed 12 electrons. Because we can only place two more electrons, we will not be able to fill up the 3p shell to 3p6; we can only fill it to 3p2, giving answer [C]. 1s2 2s2 2p6 3s2 3p2

Consider the gaseous reaction: X(g) + Y(g) → XY(g) A mixture of 0.8 mole of gas X and 1 mole of gas Y was allowed to react at 300 K in a 1 L sealed container. At the end of the reaction, what is the total pressure of the mixture? The temperature and volume remains constant during the reaction

We are given the initial amount of reactants and we need to determine the amount of reactants and products after the reaction. Then we use the ideal gas equation to solve for the total pressure. Looking at the balanced reaction, we know the molar ratio of X to Y to XY is 1 to 1 to 1. If we start with 0.8 mol of X and 1 mol of Y, then at the end of the reaction, we would have no more X left (all of X would have reacted). The amount of Y that reacts with 0.8 mol of X is 0.8 mol, which means that we have 0.2 mol of Y left of the reactants. We also have 0.8 mol XY formed. The total mol of gas at the end of the reaction would be 1 mol (0.2 mol of Y and 0.8 mol of XY). Using the ideal gas equation, the total pressure is: 24 atm

An unknown gas was found to have a density of 2.88 g/L at 27 oC and 1 atm. Which of the following could be the unknown gas?

We can calculate the molar mass of the unknown gas using the given density in order to identify it. The molar mass of a gas is related to its density via the equation: where ρ is the density, P is the pressure of the gas, M is the molar mass of the gas, R is the ideal gas constant, and T is the absolute temperature. Substituting the given values and solving for M:

A gas cylinder containing an unknown gas and methane, CH4, developed a leak. The unknown gas was found to effuse half as fast as methane. Which of the following could be the unknown gas?

We can use Graham's law of effusion to determine the molar mass of the unknown gas. Graham's law of effusion is written mathematically as Rate A/Rate B = sqrt molar mass B/molar mass A where r1 and r2 are the rate of effusion of gas 1 and 2, respectively, and M1 and M2 are the molar mass of gas 1 and 2, respectively. Of the given gases, SO2 has a molar mass of 64. Therefore, the unknown gas could be SO2.

All of the following statements about the molar mass of H2O are correct EXCEPT for one. Which one is the EXCEPTION? a. 18.02 g of h20 contains 6.022e23 h20 molecules b. 18.02 amu of h20 contains 1 mol h20 c. 1 mol of h20 contains 18.02 g mass d. 1 mol h20 contains 6.022 e 23 oxygen atoms e. 18.02 g h20 contains 2 * 6.022e23 hydrogen atoms

b

Which of the following statements is true regarding metals? a. metals form basic oxides b. alkali metal form stable +1 ions c. alkaline earth metals, M, react with oxygen to form a compound with a formula MO d. transition metals form brightly colored compoiunds e. all

e

What BEST describes the type of reaction portrayed in the reaction coordinate diagram below? a. endergonic b. exergonic c. endothermic d. exothermic e. spontaneous f. non spontaneous

endothermic

Consider this reaction: S2O82- + 3I- → 2SO42- + I3- Determine the rate law for this reaction given the following experimental rate data. experiment [S2O8]2-, M [I-], M instantaneous rate x10^3 1 .5 .2 2 2 .5 .4 4 3 1 .2 4

rate = k[S2O8 20][I-] The rate of this reaction is given by: Rate = k[S2O82-]x[I-]y where x and y are the order of the reaction with respect to each of the reactant. From experiment 1 and 2, we see that doubling the concentration of I- while keeping the concentration of S2O82- constant also doubles the rate. This means that the reaction is first order with respect to I-. Similarly, from experiment 1 and 3, doubling the [S2O82-] while keeping [I-] constant also doubles the rate. This means that the reaction is first order with respect to S2O82- as well. Therefore, our rate law is Rate = k[S2O8][I-]