DAT Chem Missed Questions
Given the ΔH for the reaction data set, calculate the enthalpy change for the following reaction. H2SO4(l) → SO3(g) + H2O(g) H2S(g) + 2O2(g) → SO3(g) + H2O(l) ΔH = -200 kJ H2S(g) + 2O2(g) → H2SO4(l) ΔH = -230 kJ H2O(l) → H2O(g) ΔH = 45 kJ
+75 kJ; write rxns, cancel, flip, and multiply (including delta H values) as needed to get the right equations to add to the final target eq. Add them together to get your final deltaH value.
What is -log1?
0
What is -log0.1?
1
How many moles of oxygen are in a 13g solution of NaNO3 solution? (molar mass of NaNO3 = 85g/mol)
13*3/85. Convert to moles, perform mole to mole conversion.
According to the following reaction, how many grams of hydrogen gas is formed when 15g of aluminum reacts with excess acid? 2Al + 6HCl → 2AlCl3 + 3H2
15*3/27; Determine limiting reactant, convert to moles, perform mole ratio, convert back to grams, cancel as needed
What is -log0.01?
2
What is -log0.001?
3
A 200g sample of mercury at 25°C was heated to 75°C with the addition of 3kJ of energy. Calculate the specific heat of mercury in J/g°C.
3000/200*50. Write values, note that q=mcdeltaT can be used, where c is specific heat. Plug in values and solve for c.
Under what conditions can a supercritical fluid be changed back into a liquid or gas? A. Decrease temperature only B. Increase temperature only C. Increase both temperature and pressure D. Increase pressure only
A; A "supercritical fluid" is a substance existing in a phase that is beyond the "critical point". The critical point marks the end of the boundary between the liquid and gas phase as shown in the image below; therefore, a supercritical fluid is dense like a liquid but has low viscosity like a gas. To bring the supercritical fluid back into a liquid phase, the temperature must be decreased below the critical temperature. To bring the supercritical fluid back into a gaseous phase, the pressure must be decreased below the critical pressure.
Which of the following best describes the energy conversion process of a battery operating in a remote controller? A. Chemical to electrical B. Mechanical to chemical C. Chemical to mechanical D. Electrical to chemical E. Mechanical to electrical
A; A battery is an electrochemical cell with a positive terminal (cathode) and a negative terminal (anode) that supplies electric power (dependent on its voltage) by conducting electrons from anode to the cathode through the circuit it is connected to. The redox reaction in which a battery is supplying electric power is undergoing an energy conversion from chemical to electric due to a transfer of electrons from each half-cell (chemical) to provide current for the board (electrical).
Which of the following is a state function? A. Enthalpy B. Work C. Speed D. Power E. Heat
A; A state function is defined as a unit that depends only on the change between initial and final states of a system. A path function is defined as a unit that depends only on the process by which the change occurs. Of all the option choices, only enthalpy is a state function, because it is solely dependent on the final and initial states (and therefore can be written with the delta sign). All other options choices are path functions that depend on the process by which the process is done.
Vaporization is which of the following types of processes? A. Endothermic B. Exothermic C. Is a chemical change from solid to gas D. Is a chemical change from liquid to gas E. Is a physical change from solid to gas
A; All phase changes are physical changes, not chemical changes! During vaporization, bonds are being broken as the molecules enter the less organized and higher entropy state. In order for bonds to be broken, energy is required. Therefore, all reactions that break bonds are endothermic. As a result, when we go from solid to liquid (melting/fusion), solid to gas (sublimation) or liquid to gas (vaporization), we are breaking bonds and thus require the input of heat (endothermic) to derive the reaction forward.
Which of the following pairs are typically found in alkaline buffer solutions? A. Weak base and its conjugate acid B. Weak acid and its conjugate base C. Strong base and its conjugate acid D. Strong acid and its conjugate base E. Strong acid and its conjugate acid
A; Buffers are solutions that resist changes in pH when small amounts of acid or base are added. They consist of a mixture of either a weak acid and a salt of its conjugate base, or a weak base and a salt of its conjugate acid. The acidic component of a buffer can neutralize an added base while the basic component of a buffer can neutralize an added acid. This means that large changes in pH will be repressed. For example, CH3COOH is a weak acid, and its conjugate base is CH3COO−. As such, a buffer could be made by mixing equal concentrations of each into solution. Typically, weak bases and their conjugate are found in alkaline (pH > 7) solutions, while weak acids and their conjugates are found in acidic (pH < 7) solutions. This is because to be efficient buffers, they need to have pK values which is equal to or can be +/- 1 value different than the pH.
When A and B react to form the product C, it was determined experimentally that the rate of the reaction is second-order with respect to A and zero-order with respect to B. How will the rate constant change if the concentration of A was doubled and the concentration of B was tripled? A. 0x B. 2x C. 3x D. 4x E. 6x
A; The question is not asking about the overall rate. It is asking how the rate CONSTANT would change. The rate constant would not change, so the answer is 0x.
Each of the following are properties of transitional metals EXCEPT one. Which one is the EXCEPTION? A. Have low melting point B. Multiple oxidation states C. Form colored-compounds D. Are paramagnetic E. Have partially filled d subshells
A; Transition metals are the elements belonging to groups 3 - 12 of the periodic table, as shown in the image below. Common properties of transition elements include: • Can readily form partially filled d-orbitals • Having valence electrons in more than one orbital also leads to transition metals often exhibiting several oxidation states • Have high melting and boiling points • Are hard and have high densities • Can form compounds that are paramagnetic • Can form compounds that are excellent catalysts • Can form colored compounds
What is the pH of a 0.001M solution of a monoprotic acid with a Ka value of 9 x 10-7? A. -log[3 x 10-5] B. -log[3 x 10-6] C. -log[3 x 10-4] D. -log[3 x 10-7]
A; decide if acid is weak or strong. If the Ka is less than 1, its weak. Thus we can use the equation Ka=[H+][A]/[HA]. Knowing it is a monoprotic acid, we can determine that H and A will be produced in the same numbers as HA is consumed. Thus, the equation becomes [X][X]/[HA]. We can rewrite this to solve for X, or the H+ ion concentration using algebra. (X=sqrt(Ka*HA)). Plug in the Ka and Ha given in the problem to solve for H+. Then, we know that pH= -log[H+]. Plug in the H+ value that you found and get your answer.
Which of the following solutions has the highest boiling point? A. 0.10m K2SO4 B. 0.10m NaCl C. 0.10m NaNO3 D. 0.10m KNO3 E. 0.10m KCl
A; remember the BP elevation equation: deltaTb=iKbm. i, vant hoff factor, is the only variable that we're interested in since everything else is constant. The highest i will have the highest BP elevation. i is the number of ions/molecule formed after dissolving. Calculate i for each choice and choose the highest one.
Bromine exists as two stable isotopes: 50.69% 79Br and 49.31% 81Br. Whereas, hydrogen exists as 99.98% 1H and 0.02% 2H in nature. What are the possible peaks for the isotopes of HBr on the NMR spectrum? A. Peaks for mass: 80 (1H and 79Br), 81 (2H and 79Br), 82 (1H and 81Br), and 83 (2H and 81Br) B. Peaks for mass: 80 (2H and 79Br), 81 (1H and 79Br), 82 (1H and 81Br), and 83 (2H and 81Br) C. Peaks for mass: 80 (1H and 79Br), 81 (2H and 79Br), 82 (2H and 81Br), and 83 (1H and 81Br) D. Peaks for mass: 80 (2H and 79Br), 81 (2H and 79Br), 82 (1H and 81Br), and 83 (1H and 81Br)
A; write out the amus for each element, add the elements together that would be in each possible compound, find the peaks that match these values.
Rank the following ions from largest to smallest radius: S2-, Cl-, K+, Ca2+ (strategy)
Among isoelectronic species, atoms or ions that share the same electronic configuration, the primary difference is the number of protons in each species. Higher atomic number species have more protons so they will attract electrons more tightly than another isoelectronic species with fewer protons which decreases their radii. More quantitatively, the difference between isoelectronic species is their effective nuclear charge, Zeff. This is defined as the net positive charge that electrons feel and is equal to the number of protons minus the shielding constant which is generally related to the number of inner electrons. Since isoelectronic species have the same electronic configuration, the shielding constant is comparable among isoelectronic species. Thus, the main factor to consider in determining the relative size of electronic species members is the number of protons.
Aqueous NH3 was titrated with HBr until endpoint was reached. The resulting solution was tested using four different pH indicators. Information about the indicators and the color of the indicator during the test is given in the table below. What is most consistent with the information provided? (given table of each pH change) A. pH at endpoint is 4.8 B. pH at endpoint is 6.1 C. pH at endpoint is 12.0 D. pH at endpoint is 2.4 E. pH at endpoint is 7.0
An effective indicator for a titration experiment is one that has a pH range that includes the endpoint. Recall, the end point is where the indicator just changes color, which is basically the equivalence point where the moles of titrant equals the moles of solution of unknown concentration. Often, the indicator's color at endpoint is a mixture between the color at a pH lower than the range and the color at a pH higher than the range. Returning back to the question, based on the information provided, we can determine that the pH at endpoint is between 4.2 and 6.3 because the solution changes Methyl red to an orange color. This eliminates all of the option choices except for option A and option B. Option B is incorrect because if the pH at endpoint is 6.1, then the Bromocresol Purple would likely be an intermediate color between yellow and purple. Therefore, the answer is Option A. the pH at endpoint is 4.8. (Look at what color the solution turns and use the indicators to rule out what colors did not change. If it is between a color then we can assume that the pH is between those two ranges).
What states that electrons occupy lower energy orbitals before occupying higher energy orbitals?
Aufbau Principle
Samples analyzed from a variety of sources possess the same ratio of elements within each sample. Which of the following describes these samples? A. Colloid B. Compound C. Heterogenous mixture D. Pure element E. Homogenous mixture
B; A compound is a substance composed of multiple elements that are found in a fixed stoichiometric ratio (e.g. H2O). Compounds will possess the same chemical makeup regardless of where they are obtained because they are built in a fixed proportion of atoms. The question stem's requirements of multiple atom types and fixed ratios of constituents are all satisfied by this answer.
Which type of glassware sits below the burette in an acid-base titration? A. Buchner funnel B. Erlenmeyer flask C. Beaker D. Volumetric flask E. Graduated cylinder
B; An Erlenmeyer flask is a flat bottom, conical flask with a short cylindrical neck that is used to hold liquids. An Erlenmeyer flask is often used in titrations to hold the solution of unknown concentration. An Erlenmeyer flask is used instead of a beaker because the solution can be swirled safely, without the risk of the reagents spilling or sloshing out. As shown in the image below, an Erlenmeyer flask sits below the burette in a setup for titration.
Which pairing will result in a buffer system? A. 1M HCl and 0.5M NaCH3COO B. 0.5M HCl and 1M NaCH3COO C. 1M HCl and 1M NaOH D. 1M NaOH and 1M KOH
B; An effective buffer system is between a weak acid/base and its conjugate. In fact, a buffer system is most effective when pH = pKa. Using the Henderson-Hasselbalch equation, we can see that pH = pKa occurs when we have equal concentrations of an acid and it's conjugate base. (pH= pKa+log(conj base/acid)). When a strong acid reacts with a weak base, the reaction goes forward until the limiting reagent is used up. Thus, in certain conditions, if we have half the effective concentration of strong acid relative to weak base, then we can make a 1:1 preparation. The buffer is effective when the pKa is ±1. 0.5M HCl and 1M NaCH3COO is correct because 0.5M HCl reacts with 1M NaCH3COO, resulting in 0.5M NaCH3COO and 0.5M of it's conjugate, CH3COOH. NaCH3COO acts as the limiting base. Titration between a strong acid and a strong base will lead to a neutralization reaction and not an effective buffer system.
Which of the following elements exists as a diatomic gas in its standard state and contains a double covalent bond? A. Krypton B. Oxygen C. Nitrogen D. Bromine E. Chlorine
B; Diatomic molecules are molecules composed of only TWO atoms, of the same or different chemical elements. If a diatomic molecule consists of two atoms of the same element, such as hydrogen (H2) or oxygen (O2), then it is said to be homonuclear. If a diatomic molecule consists of two different atoms, such as carbon monoxide (CO), the molecule is said to be heteronuclear. Seven elements exist as diatomic molecules in their standard elemental state in the periodic table. These seven elements are: hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine (Have No Fear of Ice Cold Beer). Atoms of these elements form covalently bonded pairs by sharing valence electrons and occur naturally as H2, N2, O2, F2, Cl2, Br2, and I2, respectively. Due to differences in orbitals and the number of valence electrons, H2, F2, Cl2, Br2, and I2 can achieve a full valence shell by forming a pair with only a single covalent bond, but O2 must form a double bond and N2 must form a triple bond.
In a fission reaction, uranium-235 is bombarded with a neutron and decays into two main radioactive fragments and 3 neutrons as depicted in the following reaction: 235U + 1n → 141Ba + X + 31n What is the element and the atomic mass of radioactive fragment X? A. 92U B. 92Kr C. 95Kr D. 92Ba
B; First, find the mass numbers knowing that the products and reactants total must equal eachother. Then, do the same with the atomic numbers to find what element it should be.
Nitrogen gas, hydrogen gas, and ammonia gas were put into a chamber and allowed to react until equilibrium was reached. The reaction is outlined by the following equation: N2(g) + 3H2(g) → 2NH3(g) If the pressure at equilibrium was more than the initial pressure, what can be said about the reaction quotient and the direction of reaction as the reaction progressed toward equilibrium? A. Qc > Kc ; forward reaction B. Qc > Kc ; backward reaction C. Qc < Kc ; forward reaction D. Qc < Kc ; backward reaction E. Qc = Kc ; backward reaction
B; First, see which side has more moles of gas. Notice that the pressure is increasing, but not by an external means. This means that it must be going towards the side that has more moles of gas to increase pressure. Note that Q>K when there are more products than reactants and the equilibrium shifts left. Then you have your answer.
All of the following are true regarding Galvanic cells EXCEPT one. Which one is the EXCEPTION? A. Oxidation occurs at the anode B. Functions to produces chemical energy C. Electrons flow from anode to cathode D. Salt bridge keeps solutions electrically neutral E. Cathodes are where metal electrodes gain electrons
B; Galvanic cells are electrochemical cells which release electrical energy from spontaneous oxidation-reduction reactions. Although chemical energy is used, a Galvanic cells purpose is to produce ELECTRICAL energy.
What quantity of a 1.0M NaOH solution is required to neutralize 15mL of a 0.5M HCl solution? A. 5.0 mL B. 7.5 mL C. 10 mL D. 12.5 mL E. 15 mL
B; Identify knowns, use M1V1=M2V2. Since we are dealing with monoprotic acids, for every 1M of acid and base used, we also make 1M of OH- and H+. Plug in known values and solve for the unknown volume in mL.
Which of the following BEST describes nuclear binding energy? A. The energy needed to hold electrons and protons together B. The energy required to disassemble the nucleus of an atom into its components C. The energy needed to remove an electron from an atom D. The energy needed to raise the temperature of a compound E. The energy released due to nuclear fusion
B; Nuclear binding energy is the energy required to split a nucleus of an atom into its component parts: protons and neutrons, or, collectively, the nucleons. It is mainly used to determine whether fission or fusion will be a favorable process. The binding energy of nuclei is always a positive number, since all nuclei require net energy to separate them into individual protons and neutrons.
Radioactive decay is the spontaneous breakdown of an atomic nucleus resulting in the release of energy and matter from the nucleus. What order kinetics does radioactive decay follow? A. Zero-order kinetics B. First-order kinetics C. Second-order kinetics D. Third-order kinetics
B; Radioactive decay, is the emission of a particle or a photon that results from the spontaneous decomposition of the unstable nucleus of an atom. The rate of radioactive decay is an intrinsic property of each radioactive isotope that is independent of temperature and the chemical and physical form of the radioactive isotope. Radioactive decay is a first-order reaction because the time required for half of the nuclei in any sample of a radioactive isotope to decay is a constant, called the half-life of the isotope. Remember, the rate of reaction is proportional to the concentration in first order kinetics In radioactive decay the number of radioactive atoms decaying per unit time is proportional to the total number of radioactive atoms present at that time.
Which of the following is a neutral salt? A. NaF B. NaCl C. NaH2PO4 D. NH4Cl
B; Salts may be defined as the product of a neutralization reaction of an acid and a base. The neutralization of any strong acid with a strong base always results in a neutral salt product. However, salts can also be acidic or basic, as well as neutral. To determine the acid-base properties of salt, we must consider the strengths of the reactant acid and base that make up the salt. For example, the neutralization of a strong acid with a weak base results in an acidic salt. In comparison, the neutralization of a weak acid with a strong base results in a basic salt. Based on this, Option B. NaCl is the only neutral salt since both cation and anion are derived from strong conjugates. Most group 1 and 2 metals form strong bases. As a result, their conjugates are neutral. Therefore, the cation half containing Na will be neutral.
Calcium chromate (CaCrO4) is a yellow solid with a Ksp of 7.1 x 10-4. Determine the ion product constant and whether a precipitate would form when an aqueous solution contains 26 mM of Ca2+ and 29 mM of CrO42-. A. IP = 7.54 x 10-4; no, precipitation will not occur B. IP = 7.54 x 10-4; yes, precipitation will occur C. IP = 754 x 10-4; no, precipitation will not occur D. IP = 754 x 10-4; yes, precipitation will occur
B; Write chemical equation, determine IP constant equation, multiply/convert as you add the given concentrations into your IP constant equation, compare IP to Ksp and if IP is bigger there WILL be a precipitate (saturated, shifts left).
Which of the following compounds contains chlorine with an oxidation number of +3? A. HClO B. HClO2 C. HClO3 D. ClO2 E. HClO4
B; determine the element we are finding oxidation states for, remember that H is +1 and O is -2, calculate the oxidation states with Cl to find out what Cl must be to achieve the correct charge. Find the oxidation state that matches the prompt.
A NaOH solution has a molarity of 2.00 M and is titrated with 75.0 mL of 0.500 M H2SO4. What volume of NaOH is needed to reach the end point? A. 0.01875 L B. 0.03750 L C. 0.0500 L D. 0.0750 L E. 0.1500 L
B; write knowns, write balanced equation, find starting mole value to work from, perform stoichiometry to get ending mole value, use molality to find the volume.
Which of the following would cause a random error? A. pH meter calibrated incorrectly B. Reading the meniscus at a different angle each time C. Spilling the product D. Electronic balance tarred incorrectly E. Thermometer reading 103°C in pure boiling water
B; • Random errors are caused by inconsistent methods of collecting the data, or inconsistent fluctuations in the environment where the experiment is carried out, affecting the outcome in unpredictable ways. For example, reading the meniscus at a different angle each time will cause random error as the measurements will fluctuate in both directions and to different extents (above and/or below the true value, varying greatly). • Systematic errors are caused by consistent inaccuracies in data collection. As a result, systematic errors skew the data towards one direction (above or below the true value and by the same extent each time). These errors often result from incorrectly calibrated instruments such as pH meters, thermometers and balances. For example, a thermometer reading 3°C higher than the true temperature will result in data that is consistently 3°C higher. Since random errors cause unpredictable fluctuations, the only method to minimize the uncertainty caused by random errors is to collect more data and compute a more accurate average. Since systematic errors cause consistent fluctuations, uncertainty caused by systemic errors can be reduced through statistical analysis. Note that a mistake is not categorized as either a random error nor systematic error. Spilling the product is an example of a mistake.
Which of the following represents the highest value of pressure? A. 100 kPa B. 1 atm C. 780 mmHg D. 25 torr E. 96,000 Pa
C; 1 atm = 101,325 Pascals = 760 mmHg = 760 torr
Which of the following BEST describes a Bronsted-Lowry base? A. Dissociates to form hydroxide (OH-) ions B. Proton donor C. Proton acceptor D. Electron pair acceptor E. Electron pair donor
C; Arrhenius bases dissociate to form hydroxide (OH-) ions. Arrhenius acids dissociate in water, forming proton (H+) ions. Lewis bases are electron pair donors. Lewis acids are electron pair acceptors. Bronsted-Lowry base is a chemical species that accepts a proton. Bronsted-Lowry acid is a chemical species that donates a proton. Acids that can donate more than one proton are called "polyprotic acids" and produce more than one ionic species
When dissolved, which molecule will cause the greatest increase in the boiling point of the solvent? A. NaCl B. NaNO2 C. MgCl2 D. NH4OH E. C6H12O6
C; Colligative properties are defined as properties of solutions that depend on the number of solute particles that can form within solution (van't Hoff factor) and not on the identity of the chemical compound. There are three colligative properties that you should know for DAT: — Vapor pressure lowering (Raoult's Law) — Boiling point elevation/freezing point depression — Osmotic pressure. The change in boiling point elevation depends on three factors: van't Hoff factor of solute (i), ebullioscopic constant of solvent (Kb), and molality of solution (m). In this question, the comparison of van't Hoff factor (i) would decide which solute would give the highest boiling point elevation. The van't Hoff factor is based upon theoretically the maximum number of ions that can be produced in solution. (DeltaTb=i*Kb*molality), so Kb will decide our answer.
Which of the following is NOT an example of a colligative property of a liquid? A. Boiling point B. Freezing point C. Heating point D. Osmotic pressure E. Vapor pressure
C; Colligative properties are properties that can only be applied to solutions and they depend on the amount or concentration of the solute in a solution. The type of solute itself does not affect colligative properties. All of the option choices (Boiling point, Freezing point, Osmotic pressure, and Vapor pressure) are colligative properties. Heating point is the only non-colligative property listed, and thus it is the correct answer.
Which of the following elements is a metalloid? A. Aluminum B. Titanium C. Antimony D. Gallium E. Tin
C; In the periodic table, elements can be broadly classified as metals, metalloids, and nonmetals. Metalloids share some characteristics of metals and some characteristics of nonmetals. Physically, metalloids are typically solid, metallic in lustre, more brittle than metal, and semi-conductive (allow for the average transmission of heat). Chemically, they mostly resemble the behaviour of non-metals, and form alloys with metals. The 7 metalloids are: Boron (B), Silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb), Tellurium (Te), and Astatine (At). They are found along the stair-step (or zig-zag) line on the periodic table.
Assuming no heat is lost to the surrounding, what is the final temperature when 100.0 mL of water at 90.0 °C is added to 200.0 mL of water at 10.0 °C? A. 25°C B. 30°C C. 35°C D. 40°C E. 45°C
C; Notice that there is no heat lost to the surroundings so H loss warm water= H loss cold water). Use this to identify equation M1(delta T1)(Cp1)=M2(delta T2)(Cp2). This will come out to M1(T1-TF)=M2(TF-T2), where T1 is 90degC and T2 is 10degC. Calculate the mass values by multiplying the density of water (1 g/mL) times the volumes of the water. Plug the mass volumes into the equations along with T1 and T2, then algebraically solve for Tf.
The nuclear binding energy of sodium-21 is 7.77MeV and the binding energy of sodium-23 is 8.11MeV. Which statement is true about these two isotopes? A. Sodium-21 is more stable B. Sodium-21 has greater mass C. Sodium-23 has a greater mass defect D. Sodium-23 is less likely to lose an electron E. Sodium-23 has greater intermolecular force
C; Nuclear binding energy is the energy required to disassemble the nucleus of an atom into its separate nucleons (protons and neutrons). The greater the binding energy, the more stable the nucleus is and the less likely it is to decay by losing a proton or neutron. The equation to calculate nuclear binding energy is: E=mc^2. Mass defect is the difference in the mass of the nuclei and the total mass of its constituent nucleons. For example, the mass of helium on the periodic table is 4.00 amu. However, the mass of 2 protons + 2 neutrons is 4.03 amu; therefore, there is a mass defect of 0.03 amu. Based on the equation, nuclear binding energy is proportional to the mass defect; the greater the mass defect, the greater the nuclear binding energy. Nuclear binding energy has no relation to intermolecular nor intramolecular forces, nor electron affinity.
What is the number of parts per million (ppm) of NaCl in a 0.50% saline solution? A. 50 B. 500 C. 5,000 D. 50,000 E. 500,000
C; PPM is a fraction out of a basis of 1,000,000. 1 percent is 10,000ppm (1,000,000/100=10,000), so we can multiply 0.5% * 10,000 to get 5000 ppm.
If 5 moles of oxygen gas are present in a 5L container at a temperature of 25oC, which of the following is the pressure of oxygen gas? (R = 8.314 L • kPa • K−1 • mol−1) A. 2300 kPa B. 2400 kPa C. 2500 kPa D. 2600 kPa E. 2700 kPa
C; PV=nRT rearranged to solve for P
At a temperature of 273K, methanol has a density of 0.792 g/cm3. How large would a container need to be to hold 0.060kg of methanol? A. 65 cm3 B. 70 cm3 C. 75 cm3 D. 80 cm3 E. 85 cm3
C; Use Density=Mass/Volume. Rearrange to get Density=Mass/Pressure. Plug in mass given (0.060kg) and density given (0.792 g/cm^3) to get V.
Which of the following molecules produces an acidic solution when placed in water? A. NaCl B. KBr C. NH4Cl D. LiF A. RbI
C; We have to find out which compound has a cation that is the conjugate acid of a weak base along with a neutral anion (the conjugate base of a strong acid). If the anion is the conjugate base of a weak acid and the cation is neutral, then the salt is basic. Neutrals are conjugates of strong bases/acids.
How many equivalent resonance structures can be drawn for the carbonate ion, CO32- ? A. 1 B. 2 C. 3 D. 4 E. 5
C; find number of electrons, draw structures without violating octet rule, and count the number of structures you can draw.
The distance separating two adjacent carbon nuclei is 1.54 Å and the bond length in F2 is 1.32 Å. Based on this data, which of the following is the length of the C-F bond in CF4? A. 1.21 B. 1.36 C. 1.43 D. 1.54 E. 1.62
C; take the average of the bond lengths given to get resulting bond length.
Which of the following is NOT an intramolecular force? A. Polar covalent bonds B. Metallic bonds C. Ionic bonds D. Van der Waals forces E. Non-polar covalent bonds
D; All of the options listed are intramolecular forces except for Van der Waals forces which is an intermolecular force. Other intermolecular forces include Hydrogen Bonding and the various kinds of dipole interactions mentioned previously. Within intermolecular forces, hydrogen bonding (H bonded to N, O and F) is the strongest, followed by Dipole-Dipole forces, and finally, London dispersion forces, both of which are considered to be Van der Waals forces. A hydrogen bond is an electrostatic force of attraction between a hydrogen atom which is covalently bound to a more electronegative atom or group, like nitrogen, oxygen, or fluorine and another electronegative atom bearing a lone pair of electrons.
Which of the following statements best describes Boyle's law? A. Volume of a gas is directly proportional to pressure B. Volume of a gas is directly proportional to its temperature C. Volume of a gas is inversely proportional to temperature D. Volume of a gas is inversely proportional to pressure E. Pressure is inversely proportional to temperature
D; Boyle's law states that at equal temperature and moles of gas, pressure is inversely proportional to volume. According to the kinetic molecular theory of gases, pressure results from the number of collisions that gas particles make with the walls of a container. Decreasing volume while maintaining the same temperature and the same number of gas particles, increases the number of collisions with the walls of the container and increases the pressure. Consequently, pressure and volume are inversely proportional, and every gas has a particular pressure-volume constant at a given temperature. Boyle's law describes this inverse relationship between volume (V) and pressure (P) for a fixed number of molecules of an ideal gas at constant temperature, where k is a constant: P is proportional to 1/V, PV=k.
A 20g block of ice is at -10°C temperature. What is the total energy required to heat the ice 50°C above boiling temperature? (heat of fusion of water = 334 J/g, heat of vapourization of water = 2257 J/g, specific heat of ice = 2.09 J/g·°C, specific heat of water = 4.18 J/g·°C, specific heat of steam = 2.09 J/g·°C). A. 24 200 J B. 36 400 J C. 58 400 J D. 62 600 J E. 72 100 J
D; Determine every step taking place, including heating and phase changes. Use q=mcdeltaT for heating the same phase and q=mcDeltaH for phase changes. Calculate a q for each step then add them up to get the heat total.
To electroplate a piece of copper metal with zinc, what reaction must occur at the cathode? A. Cu2+ + 2e- → Cu B. Cu → Cu2+ + 2e- C. Zn → Zn2+ + 2e- D. Zn2+ + 2e- → Zn
D; Electroplating is the process of plating one metal with another metal using an electrolytic cell. The piece of metal to be plated is made into the cathode because reduction always occurs at the cathode. As electrons are transferred from the anode to the cathode, the positive Zn2+ ions are attracted to the negative cathode and reduction occurs, producing Zn that deposits on the copper metal. In this question, the piece of metal to be electroplated is a piece of copper metal and the anode consists of a sacrificial piece of zinc. Use piece of metal to be plated, remember that reduction occurs at the cathode.
Each of the following are single-replacement reactions that occur EXCEPT one. Which one is the EXCEPTION? A. 2 HCl(aq) + Zn(s) → ZnCl2(aq) + H2(g) B. 2 NaCl(aq) + F2(g) → 2 NaF(s) + Cl2(g) C. CaI2(s) + Cl2(g) → CaCl2(s) + I2(s) D. CaF2(s) + Br2(ℓ) → CaBr2(s) + F2(g) E. 2 Fe2O3(s) + 3 C (s) → 4 Fe(s) + 3 CO2(g)
D; Halogens will not replace another halogen that is higher than them on the periodic table. For this to happen, the other halogen would have to be lower.
Each of the following are ionic compounds EXCEPT one. Which one is the EXCEPTION? A. NH4NO2 B. KH C. LiNO3 D. CH3NH2 E. NaOH
D; Ionic compounds are chemical compounds composed of ions. Ionic compounds are formed by ions with opposite charges binding together through electrostatic force termed ionic bonding. In contrast, covalent compounds contain electrons that are shared between bonded atoms and are simultaneously attracted to more than one nucleus. CH3NH2 is the only option that is NOT an ionic compound. Instead, it is formed from the covalent bonding of the three hydrogen molecules to carbon and nitrogen, with carbon as the central atom. The other two hydrogens bond covalently to the nitrogen.
What is the pH of a 0.001M solution of sulfuric acid? (pKa = -2.8), assuming complete dissociation? A. 0 B. 1 C. 2 D. 3 E. 4
D; Note that [H+]=[HA]. For a polyprotic acid, we have to multiply the conc. of the acid by 2. So our [H] value would be 0.002. To get pH, we take the negative log of that and get about 2.6 which rounds to 3. (-log0.001=3 and -log0.01 is 2 so it must be somewhere in between these numbers.
Which of the following is true regarding pi bonds and sigma bonds? A. Pi bonds are stronger than sigma bonds B. Sigma bonds are formed from lateral orbital overlap C. Pi bonds allow rotation D. A triple bond contains one sigma and two pi bonds E. Pi bonds are formed from end-to-end orbital overlap
D; Sigma bonds are covalent bonds made by the end-to-end overlap of atomic orbitals, while pi bonds are covalent bonds made by the side-to-side (lateral) overlap of p-orbitals. Although some atoms only participate in single covalent bonding, other atoms are capable of participating in multiple bonds by the addition of one or more pi bonds. In this way, a double bond consists of one sigma bond and one pi bond. A triple bond consists of one sigma bond and two pi bonds, as shown in the table below. Pi bonds are weaker than sigma bonds as end-to-end overlap in sigma bonds is stronger than lateral overlap in pi bonds.
What row represents elements with increasing atomic radii? A. Na , Li, Be, B B. Be, Li, Na, Mg C. Na, Mg, Al, Si D. B, Be, Li, Na E. C, B, Na, Mg
D; The atomic radius is one-half the distance between the nuclei of two atoms measured in picometers. Atomic size gradually decreases from LEFT to RIGHT across the periodic table as electrons are added to the same shell. However, at the same time, protons are being added to the nucleus, making it more positively charged. Since the effect of increasing proton number is greater than that of the increasing electron number; there is a greater nuclear attraction causing this trend as the valence electrons are held closer towards the nucleus of the atom. Furthermore, the atomic radii decreases from BOTTOM to TOP.
An aqueous mixture contains CuF2 and BaF2 (Ksp = 3.0×10−6). What should be added to the solution in order to precipitate CuF2? A. NaF B. H2O C. Ba(NO3)2 D. Cu(NO3)2
D; The common ion effect says that if a solution contains two salts that have a common ion, the common ion supplied by one salt introduces a common ion effect that disturbs the solubility equilibrium of the other salt. This causes its equilibrium to shift left toward the reactants. The common ion effect is essentially a specific scenario involving Le Châtelier's principle, which states that if an equilibrium is disrupted, the equilibrium will shift to minimize the change and establish a new equilibrium. In order to precipitate CuF2 from a solution mixture of CuF2 and BaF2, Cu2+ ions need to be introduced into the solution. The increase in Cu2+ concentration disturbs the product side of the solubility equilibrium and causes it to shift toward the reactants. Therefore, adding Cu(NO3)2 as a source of Cu2+ ions will selectively cause the CuF2 in the mixture to precipitate.
The point above which a gas cannot be converted into a liquid is known as what? A. Triple point B. End point C. Equivalence point D. Critical point E. Inflection point
D; The critical point is located at the end of the vaporization/condensation curve (blue line) between liquid phase and gas phase. Above this point contains a medium called supercritical fluid, in which it cannot be distinguished as liquid or solid and is merged as one (sometimes this is called plasma). Thus, above the critical point, neither gas nor liquid can be converted from one to another.
Which one of the following molecules is polar? A. CCl4 B. PCl5 C. CO2 D. H2S E. CH4
D; To determine the most polar molecule, we must draw out the VESPR diagrams for each option choice. Note: Keep in mind, just because a bond is polar does NOT mean that the entire molecule as a whole is polar as well. Remember, dipoles can cancel each other out. "Will the truck move". Draw vectors and decide. If it does, its polar.
Which of the following is the correct molecular geometry of PCl5 ? A. Bent B. Trigonal planar C. Tetrahedral D. Trigonal bypyramidal E. Octahedral
D; When we draw the molecule we see it has no lone pairs and 5 bonds. That is trigonal bipyramidal.
A container holds 4.0L of gas at 3.5 atmospheres and a temperature of 27oC. If the pressure is reduced to 0.8 atmospheres without a change in temperature, what would be the volume of the gas? A. 11.0 L B. 14.0 L C. 15.0 L D. 18.0 L E. 19.0 L
D; Write knowns, write equation (Boyle's Law) P1V1/n1T1=P2V2/n2T2. Cancel constants, plug in knowns, solve for unknowns. Round to nearest whole #.
How many electrons are involved in the following basic redox reaction? 4Zn + NO3- + 7OH- + 6H2O → 4Zn(OH)42- + NH3 A. 2 B. 4 C. 6 D. 8 E. 10
D; write half rxns, balance oxygens with water, balance waters with H+, in basic solution balance H+ with OH- (on both sides). Add electrons to get charge the same on both sides, make sure both half reactions have the same amt of electrons to cancel, sum together and take the number of electrons you used.
What gas law states that two gases of equal volumes will also have equal number of molecules at the same temperature and pressure? A. Boyle's Law B. Dalton's Law C. Gay-Lussac's Law D. Charles' Law E. Avogadro's Law
E
Which of the following element has the LOWEST electron affinity? A. Li B. B C. O D. F E. Ne
E; Exception: Group VIII of the periodic table (Noble gases) is quite special because they already have eight valence electrons, which fill their outer energy level. They can't accept any more electrons, therefore, the electron affinity of nobles gases is practically zero. Option E. Neon has the lowest affinity because its outermost shell is completely filled with electrons.
Which substance reacts with water most violently to produce H2 gas? A. Be B. C C. N D. O E. Li
E; For DAT, it is important to know that elements that are highly reducing (i.e., alkali metals and alkaline earth metals) are ones that are highly reactive in water. They react according to the following chemical equation. Alkali Metals: 2 M(s) + 2H2O (l) → 2 MOH (aq) + H2 (g) Alkaline Earth Metals: M (s) +2 H2O (l) → M(OH)2 (aq) + H2 (g). The reason why these metals are highly reactive with water is that they will combust to form metal hydroxides and hydrogen gas, both of which will produce highly vigorous exothermic reaction when exposed to water vapor. Between the alkali metals and alkaline metals, alkali metals are more reactive.
An 84 g sample of a compound is found to contain 36 g of carbon, 3 g of hydrogen, 21 g of nitrogen, and 24 g of oxygen. If the compound has a molecular weight of 112 g/mol, what is its molecular formula? A. C2H2NO2 B. C2H2NO C. C5H2NO D. C4H3NO E. C4H4N2O2
E; Get each element in moles. Divide by the smallest mole value on each to get empirical formula. Find out empirical formula MW. Multiply as needed to get the MW given so that formula will match.
Which of the following enthalpy changes is correctly arranged from highest to lowest? A. ΔH°vaporization > ΔH°sublimation > ΔH°fusion B. ΔH°vaporization > ΔH°fusion > ΔH°sublimation C. ΔH°fusion > ΔH°sublimation > ΔH°vaporization D. ΔH°sublimation > ΔH°fusion > ΔH°vaporization E. ΔH°sublimation > ΔH°vaporization > ΔH°fusion
E; In a heating curve, a pure substance must overcome intermolecular forces in order to go through phase changes. There are two types of transitions when calculating the heat absorbed: calorimetry and enthalpy. Calorimetry corresponds to the portions of graph with sloped lines (single-phase: solid, liquid, gas). Enthalpy corresponds to portions of the graph with horizontal lines (phase transitions: melting (solid → liquid) and boiling (liquid → gas)). Because the boiling requires higher heat to be absorbed due to the complete dissolution of intermolecular forces than melting, . By Hess's Law, sublimation is defined as the sum of vaporization and fusion, so it is the highest.
What is the bond angle that exists within a molecule of SO3? A. 90 B. 104.5 C. 107 D. 109.5 E. 120
E; To determine the bond angle of sulfur trioxide, we must first determine its lewis structure. By doing this, we learn that sulfur trioxide molecule has a sp2 configuration as well as a trigonal planar VESPR geometry. It is important to note that trigonal planar molecules have bond angles of 120 degrees. This is partially because sulfur can have an expanded octet (have more than 8 bonds) due to the 3d-orbital that it possesses.
Given the titration curve below, what quantity of 0.1 M HCl is required to reach the equivalence point in the titration with 0.1 M of NH3? (Approach)
Find the equivalence point on the graph (middle of vertical line), taking the associated volume. Use the equation Quantity of acid delivered= (vol titrant added)(titrant conc). Now, we multiply (value of equivalence point on graph)(0.1 titrant conc) to get ten. Since the ratio is 1:1 that is our answer. (NH3 and HCl dissociate into one mole of base and acid respectively)
How much energy is required to bring 250mL of water (4.18J/g°C) to a boil if the initial temperature is 25°C? (Strategy)
Find the grams of water using the density of water 1g/mL*250ml given = 250g. Then, use q=mcdeltaT. q=(mass calculated)(4.181)(100 aka boiling temp of water - 25degC)
At which point during a titration experiment does pH = pKa ?
Half-equivalence point
What states that electrons singly occupy separate orbitals of the same energy level before pairing up to occupy the same orbital?
Hund's Rule
An experiment is conducted and the titration curve was recorded as shown below. What was titrated to create to this curve? (Problem approach)
In a titration experiment, a measured amount of an acid or a base solution of a known concentration is slowly added to another solution containing a base or an acid of an unknown concentration. During this experiment, the acid or base being titrated is fully neutralized at the equivalence point. When this occurs, the pH changes rapidly when passing through the equivalence point is seen as a nearly vertical segment on a titration curve. The equivalence point is located in the middle of this vertical segment. Going back to the question, we know that since the pH at the start of the solution is 10, as shown in the image below, the solution was initially a base. At the end of the curve, the pH is 2 and therefore the solution turned acidic. The only way to turn a basic solution acidic is by adding a strong acid to an already weak base. So we know that we must have been using a weak base with a strong acid because we start with a basic solution. It's the opposite if you're starting with an acidic solution.
Which of the following reactions has an equilibrium point that would NOT be affected by a change in pressure? (Strategy)
Le Chatelier's principle states that the equilibrium point will be shifted in response to a change in temperature or concentration that disturbs the original dynamic equilibrium. A change in pressure will affect the equilibrium point if the number of moles of gas in the reactants is different than in the products. An increase in pressure will cause the equilibrium to shift to the side that has fewer moles of gas, and a decrease in pressure will cause the equilibrium to shift to the side that has greater moles of gas. Use coefficients to figure this out.
Based on the given data, what is initial activity of the radioactive sample at zero hours if the half-life is 12 hours? (Strategy)
Note that at the time at 12 hours, the initial amount has been halved. So we have to multiply that by two to get back to the initial amount.
When NaCl was dissolved in 1 kg H2O (Kf = 1.86 ºC/m), the freezing point of the solution was lowered by 5.58 ºC. What is the value of Kf for benzene if the same amount of NaCl was dissolved in 2 kg benzene and the freezing point was lowered by 15.36 ºC? (approach only)
Note that we are looking for the Kf value. First, we need to find out how many moles of NaCl we have. We do this by using deltaTf=-i*Kf*m to first find the molality. We rearrange to solve for the molality, using the Vant hoff factor of NaCl which is 2. We then multiply this value by the mass given for solvent to get the moles NaCl. Now that we have the moles, we can plug this into to deltaTf=-i*Kf*m rearranged to solve for Kf. The vant hoff factor will now be one because NaCl does not dissolve in benzene. The molality will be 1.5mol (solved for)/2kg solvent.
What is the Kw of pure water at 90°C if the Kb is 1 x 10-6? (Strategy)
Notice that it is not at room temperature. If it was, it would be 1*10^-14. However, since it is in pure water Ka=Kb. Thus if we multiply those we get Kw.
What is Gay-Lussac's Law?
P1/T1 = P2/T2
What is Boyles Law?
P1V1=P2V2
What states that electrons occupying the same orbital must have opposite spins? In other words, no two electrons of the same atom can have the same set of quantum numbers, as the spin numbers must be different.
Pauli Exclusion Principle
Quantum numbers are used to describe an electron in an atom completely. What are the four quantum numbers? 1. _____ quantum number (n) 2. ____ quantum number (ℓ) 3. ____ quantum number (mℓ) 4. ____ quantum number (s)
Principal, Azimuthal, Magnetic, Spin
What is Daltons Law?
Ptotal = P1 + P2 + P3 + ...
Consider two identical balloons, one filled with oxygen gas and another filled with hydrogen gas. Which of the following describes the difference in rate of effusion? (equation)
Rate1/Rate2=sqt(gas2)/sqt(gas 1). Solve. Remember the diatomic gases.
What is the activation energy of the following reaction? (Strategy)
This is an endothermic reaction because the energy of the products is higher than the energy of the reactants. The activation energy is the difference between the activated complex (peak of graph) and the reactants: 250 kJ - 50 kJ = 200 kJ
If you halve the pressure of a gas at constant temperature, what happens to the volume? A. Volume will be halved B. Volume will be reduced to a third C. Volume will be tripled D. Volume will double E. Volume does not change
To solve this question, we must use the combined gas law: P1V1/n1T1=P2V2/n2T2. Since the question does not specify that there is a change in gas molecules, we can assume n1 = n2. Furthermore, since temperature is also said to be constant, we can simplify the equation: P1V1=P2V2. Plug in values that match the question prompt and solve to get answer/relationship.
What would be the heat of formation for ethane gas (C2H6) if ΔHf ° for ethene gas (C2H4) is +50.5 kJ/mol? (Approach)
Use Hess's Law (Delta H reaction=Sum of Delta H products - Sum of Delta H reactants. Plug in the given delta H rxn and the delta H for ethene and use algebra to solve for ethanes delta H. Remember that hydrogens delta H is zero.
At 37°C, which one of the following solutions produces the lowest osmotic pressure? (Strategy)
Use Osmotic Pressure=iMRT. Since R and T will be constant, find the Vant hoff factor of each and multiply it by the M value. Then, see which is lowest to get your answer.
What is Charles' Law?
V1/T1 = V2/T2
Is NH3 a weak or strong base?
Weak
How do you solve a rate law problem?
Write general rate law formula (Rate=kA^x*B^y). Find matching values of B conc to solve for rate A. Put larger sum on top and lower on bottom. Simplify and solve for x. Repeat with B to get rate law.
What is the ionic reaction for the neutralization of HCl with NaOH? (strategy)
Write out equation. Note that H2O turns into liquid. Write the dissociations of each reactant as well as the products and write the final equation. Note that NaCl does NOT turn into a solid.
What is the final concentration of chloride ions when a 1 L solution of 0.100 M CaCl2 is mixed with 1 L of 0.100 M NaCl? (Approach)
Write out the rxn of CaCl2 dissociating. Balance the equation. Find out how many moles of Cl- there are by multiplying the stoichometric coeff by the given conc of CaCl2. Note this will be X M/1L of solution. Next, repeat the process with NaCl. Add the two values together and divide by the total liters (2) to get the final concentration.
Fusion, vaporization, and sublimation are ________ processes, whereas freezing, condensation, and deposition are ________ processes.
endothermic, exothermic. Changes of state are examples of phase changes. It's important to know that all phase changes are accompanied by changes in the energy of a system. Changes from a more-ordered state to a less-ordered state (such as a liquid to a gas) are endothermic. Changes from a less-ordered state to a more-ordered state (such as a liquid to a solid) are always exothermic.
At the _______, moles of base = moles of acid. However, the pH will not equal the pKa.
equivalence point
What is the symbol for the azimuthal quantum number, what are its allowed values, and what property does it show?
l, integers from 0 to (n-1), orbital shape (sublevels/subshells)
What is the symbol for the magnetic quantum number, what are its allowed values, and what property does it show?
ml, integers -l to +l, orbital orientation
What is the symbol for the spin quantum number, what are its allowed values, and what property does it show?
ms, +1/2 to -1/2, electron spin direction
What is the symbol for the principle quantum number, what are its allowed values, and what property does it show?
n, positive integers 1,2,3. Orbital size and NRG level
