AP Chem Final Exam MCQ

N₂O(g) + CO(g) → N₂(g) + CO₂(g) The rate of the reaction represented above increases significantly in the presence of Pd(s). Which of the following best explains this observation?

One of the reactants binds on the surface of Pd, which introduces an alternative reaction pathway with a lower activation energy.

H₃PO₄(aq) Ka₁ 7.5 × 10⁻³ Ka₂ 6.2 × 10⁻⁸ Ka₃ 4.2 × 10⁻¹³ The values of the dissociation constants for H3PO4 are given in the table above. Given that the solution in the beaker at the end of step 2 had a pH of approximately 1, which of the following chemical species had the lowest concentration among the products of step 2 ?

PO₄³⁻(aq)

The data from a study of the decomposition of NO2(g) to form NO(g) and O2(g) are given in the table above. Which of the following rate laws is consistent with the data?

Rate= k[NO2]^2

C(diamond) → C(graphite) ΔG°= −2.9 kJ/molrxn

The reaction has an extremely large activation energy due to strong three-dimensional bonding among carbon atoms in diamond.

A 1.0 L sample of a pure gas is found to have a lower pressure than that predicted by the ideal gas law. The best explanation for the observation is that the molecules of the gas

are attracted to each other and do not exert as much force on the container walls as they would if they had no mutual attractions

Compared to the equilibrium vapor pressure of CH3OH(l) at 300 K, the equilibrium vapor pressure of C2H5OH(l) at 300 K is

lower, because London dispersion forces among C2H5OH molecules are greater than those among CH3OH molecules

A student titrates 10.0mL samples of 1.0M solutions of each of the haloacetic acids with a standard solution of NaOH. Which of the following statements correctly predicts the volume of NaOH(aq) needed to reach the equivalence point?

All of the acids will need the same volume of NaOH(aq) to reach the equivalence point.

A 1.0mol sample of He(g) at 25°C is mixed with a 1.0mol sample of Xe(g) at 50°C. Which of the following correctly predicts the changes in average kinetic energy and the average speed of the Xe(g) atoms that will occur as the mixture approaches thermal equilibrium?

Average Kinetic Energy of Xe Atoms Average Speed of Xe Both will decrease

What is the value of E° for the cell?

1.56 V

At 25°C, enough distilled water is added to a 30.0mL30.0mL sample of HNO3(aq) with a pH of 4.20 so that the final pH of the diluted solution is 5.20. The volume of distilled water added to the original solution is closest to

270. mL

Ionization Energy(kJ/mol) First 578 Second 1,817 Third 2,745 Fourth 11,577 Fifth 14,842 The first five ionization energies of an unknown element are listed in the table above. Which of the following statements correctly identifies the element and cites the evidence supporting the identification?

Al, because of the large difference between the third and fourth ionization energies

Equal volumes of solutions in two different vessels are represented above. If the solution represented in vessel 1 is KCl(aq), then the solution represented in vessel 2 could be an aqueous solution of

CaCl2 with twice the molarity of the solution in vessel 1

The structure of haloacetic acids, XCH2COOH (where X is either F, Cl, Br, or I), is shown above. The dissociation constants and molar masses of four haloacetic acids are listed in the table below. Which compound, chloroacetic acid or iodoacetic acid, most likely has the lower boiling point, and why?

Chloroacetic acid, because the London dispersion forces among its molecules are weaker.

A student obtains a mixture of the liquids hexane and octane, which are miscible in all proportions. Which of the following techniques would be best for separating the two components of the mixture, and why?

Distillation, because the liquids would boil at different temperatures owing to the difference in strength of their intermolecular forces.

The saturated CuSO4(aq) shown above is left uncovered on a lab bench at a constant temperature. As the solution evaporates, 1.0mL samples of the solution are removed every three days and the [SO42−] in the samples is measured. It is observed that the [SO42−] in the solution did not change over time. Which of the following best helps to explain the observation?

As water evaporates, more CuSO4(s) precipitates out of the solution in the beaker.

The Maxwell-Boltzmann distributions of molecular speeds in samples of two different gases at the same temperature are shown above. Which gas has the greater molar mass?

Gas A

Which of the following most likely describes the solid represented in the diagram above?

It is a brittle, water-soluble electrolyte that is a poor thermal and electrical conductor as a solid.

Which of the following statements is true about sodium glycinate, represented above?

It is an ionic solid at room temperature.

Samples of NaF(s) and NH4Cl(s) are dissolved in separate beakers that each contain 100mL of water. One of the salts produces a slightly acidic solution. Which of the following equations best represents the formation of the slightly acidic solution?

NH4+(aq) + H2O(l) ⇄ NH3(aq) + H3O+(aq)

For which of the equilibrium systems represented below will the amount of product(s) at equilibrium increase if the volume of the reaction vessel is increased at a constant temperature?

PCl₅(g) ⇌ PCl₃(g) + Cl₂(g)

Compound Ksp at 25°C Pb(OH)₂(s) 1.2 × 10⁻¹⁵ PbI₂(s) 1.4 × 10⁻⁸ PbF₂(s) 4.0 × 10⁻⁸ Equimolar samples of Pb(OH)₂(s), PbI₂(s), and PbF₂(s) are placed in three separate beakers, each containing 250 mL of water at 25°C. After the solutions are stirred, solid remains in the bottom of each beaker. Based on the Ksp values for the compounds listed in the table above, a solution of which of the compounds will have the lowest [Pb²⁺] ?

Pb(OH)₂(s)

Based on the structural formulas, which of the following identifies the compound that is more soluble in water and best helps to explain why?

Propanol, because its molecules can form hydrogen bonds with water molecules but those of ethane cannot.

2 NOBr(g) → 2 NO(g) + Br2(g) The equation above represents an elementary step in a chemical reaction. Which of the following is the correct expression for the rate law of the elementary step?

Rate = k[NOBr]2

Which of the following best helps to explain why CCl₄ is a liquid whereas CI₄ is a solid when both are at 25°C?

The London dispersion forces are stronger in CI₄ than in CCl₄ because CI₄ has a more polarizable electron cloud than CCl₄ .

CH₄(g) + Cl(g) → CH₃(g) + HCl(g) ΔH° = −14 kJ/molrxn NH₃(g) + Cl(g) → NH₂(g) + HCl(g) ΔH° = −36 kJ/molrxn H₂O(g) + Cl(g) → OH(g) + HCl(g) ΔH° = + 40 kJ/molrxn Based on the data above, what can be concluded regarding the strength of the C −H, N−H, and O−H bonds in the molecules shown?

The O−H bond is the strongest.

The diagram above represents a particle in aqueous solution. Which of the following statements about the particle is correct?

The particle must be an anion because the positive end of each water molecule is pointed toward it.

An aqueous solution contains small but equal concentrations of both chloroacetic and fluoroacetic acids. Which statement comparing the percent ionizations of the two acids in the solution is true?

The percent ionization of chloroacetic acid is less than that of fluoroacetic acid.

H2(g) + I2(g) ⇄ 2HI(g) Hydrogen gas reacts with iodine gas at constant temperature in a sealed rigid container. The gases are allowed to reach equilibrium according to the equation above. Which of the following best describes what will happen to the reaction immediately after additional iodine gas is added to the system?

The rate of the forward reaction becomes greater than the rate of the reverse reaction.

H2(g)+I2(g)⇄2HI(g) Hydrogen gas reacts with iodine gas at constant temperature in a sealed rigid container. The gases are allowed to reach equilibrium according to the equation above. Which of the following best describes what will happen to the reaction immediately after additional iodine gas is added to the system?

The rate of the forward reaction becomes greater than the rate of the reverse reaction.

Which of the following is the most likely reason that the reaction occurs at a significant rate only if the temperature of the reaction mixture is greater than 200°C?

The reaction has a high activation energy.

A balloon filled with 0.25 mol of He(g) at 273 K and 1 atm is allowed to rise through the atmosphere. Which of the following explains what happens to the volume of the balloon as it rises from ground level to an altitude where the air temperature is 220 K and the air pressure is 0.1 atm?

The volume will increase because the decrease in air pressure will have a greater effect than the decrease in temperature.

C9H8O4(aq) + NaOH(aq) ⇄ C9H7O4−(aq) + Na+(aq) +H2O(l) The reaction represented above occurs when 2.00×10−4mol of pure acetylsalicylic acid, C9H8O4, is completely dissolved in 15.00mL of water in a flask and titrated to the equivalence point with 0.100M NaOH(aq). Which of the following statements about the titration is true at the equivalence point?

[C9H8O4] is less than [C9H7O4−].

A mixture of NO₂(g) and N₂O₄(g) is at equilibrium in a rigid reaction vessel. If the temperature of the mixture is decreased, then

[N₂O₄] will increase and the mixture will turn a lighter brown

To catalyze a biochemical reaction, an enzyme typically

binds temporarily to reactant molecules to lower the activation energy of the reaction

Solid carbon tetrachloride, CCl4(s), is represented by the diagram above. The attractions between the CCl4 molecules that hold the molecules together in the solid state are best identified as

intermolecular attractions resulting from temporary dipoles

HCHO₂(aq) + H₂O(l) ↔ H₃O+(aq) + CHO²⁻(aq) HCHO₂(aq), a weak acid (K = 2 × 10⁻⁴) a , dissociates in water according to the equation above. Which of the following provides the best estimate of the pH of 0.5 M HCHO₂(aq) and identifies the species at the highest concentration (excluding H₂O) in the solution?

pH:2 Species at highest concentration: HCHO₂(aq)

The photoelectron spectra for H and He are represented above. Which of the following statements best accounts for the fact that the peak on the He spectrum is farther to the left and higher than the peak on the H spectrum?

He has a greater nuclear charge than H and an additional electron in the same energy level.

Which of the following procedures will allow the student to determine the rate constant, k, for the reaction?

Plot ln[X] versus time and determine the magnitude of the slope.

A 50.0 g sample of Feat 100°C is added to 500.0 mL of water at 35°C in a perfectly insulated container. Which of the following statements is true?

The heat energy lost by the Fe will be equal to the heat energy gained by the water.

Which of the following is the net ionic equation for the overall reaction that occurs as the cell operates?

2Ag+(aq) + Zn(s)→ 2Ag(s) + Zn^2+(aq)

An experiment is performed to measure the mass percent of CaCO3(s) in eggshells. Five different samples of CaCO3(s) of known mass react with an excess of 2.0MHCl(aq) in identical sealed, rigid reaction vessels. The pressure of the gas produced is measured with a pressure gauge attached to the reaction vessel. Since the reaction is exothermic, the reaction system is cooled to its original temperature before the pressure is recorded. The experimental data are used to create the calibration line below. Which of the following equations best represents the species that react and the species that are produced when CaCO3(s) and HCl(aq) are combined?

2H+(aq)+CaCO3(s)→Ca2+(aq)+H2O(l)+CO2(g)

The value of Kw at 40°C is 3.0×10−14. What is the pH of pure water at 40°C?

6.8

The mass percent of CaCO3(s) in the eggshell sample is closest to

75%

CO2(g)+2LiOH(s)→Li2CO3(aq)+H2O(l) In a one-person spacecraft, an astronaut exhales 880g of CO2(g) (molar mass 44g/mol) per day. To prevent the buildup of CO2(g) in the spacecraft, a device containing LiOH(s) is used to remove the CO2(g), as represented by the equation above. What mass of LiOH(s) (molar mass 24g/mol) is needed to react with all of the CO2(g) produced by an astronaut in one day?

960g

Which of the following best describes the change that takes place immediately after the CH3OH(l) is introduced into the previously evacuated vessel?

A physical change takes place because intermolecular attractions are overcome.

CaF₂(s) ↔ Ca²⁺(aq) + 2 F⁻(aq) ΔH> 0 Dissolution of the slightly soluble salt CaF₂ is shown by the equation above. Which of the following changes will decrease [Ca²⁺] in a saturated solution of CaF₂ , and why? (Assume that after each change some CaF₂(s) remains in contact with the solution.)

Adding NaF(s), because the reaction will proceed toward reactants

The structural formula of the glycinium cation is shown above. Arrows indicate the pKa values for the labile protons in the molecule. Which of the following is true about the geometry of the glycinium cation?

Both C atoms and both O atoms lie in the same plane.

Which of the following Lewis electron-dot diagrams represents the molecule that is the most polar?

BrF

Which of the following is the molecular formula of the unknown compound?

C4H8O2

When a small amount of 12 M HNO₂(aq) is added to a buffer solution made by mixing CH₃NH₂(aq) and CH₃NH₃Cl(aq), the pH of the buffer solution changes from 10.64 to 10.62. Which of the following equations represents the reaction that accounts for the fact that the pH does not change significantly when the HNO₃(aq) is added?

CH₃NH₂(aq) + H⁺(aq) → CH₃NH₃⁺(aq)

In which of the following processes will ΔS° be negative?

Cl2(g)→Cl2(l)

As a sample of KNO3(s) is stirred into water at 25°C, the compound dissolves endothermically. Which of the following best helps to explain why the process is thermodynamically favorable at 25°C?

Dissolving the salt increases the entropy of the system.

Which of the following gives the value of E⁰cell for the cell?

E⁰cell = +0.02 V

Which of the following happens to H atoms in the forward reaction?

H atoms are both oxidized and reduced

A 20. mL sample of 0.50 M HC2H3O2(aq) is titrated with 0.50 M NaOH(aq). Which of the following best represents the species that react and the species produced in the reaction?

HC2H3O2(aq) + OH−(aq) → C2H3O2 −(aq) + H2O(l)

A solution is prepared by mixing equal volumes of 0.20M HC2H3O2 and 0.40MNaC2H3O2. Which of the following correctly describes what occurs if a small amount of HCl(aq) or NaOH(aq) is added?

If HCl(aq) is added, the pH will decrease only slightly because the H+ ions will react with C2H3O2− ions.

Reaction Keq SO₂(g) + O₂(g) ↔ SO₃(g) K₁ 2SO₃(g) ↔ 2SO₂(g) + O₂(g) K₂ Which of the following shows the relationship between K₁ and K₂ in the reactions represented above?

K₂ = 1/(K₁)²

The forward reaction is thermodynamically favored at which of the following temperatures?

Low temperatures only

Which of the following is a list of the minimum amount of data needed for determining the molar enthalpy of solution of KCl(s) in pure H2O(l) ? (Assume that the KCl(aq) has the same specific heat capacity as pure water and that the initial temperatures of the KCl(s) and the water are the same.)

Mass of KCl(s), mass of H2O, initial temperature of the water, and final temperature of the solution

H₂(g) + I₂(g) ⇌ 2HI( g) Kc = 50. at 600°C Equimolar samples of each of three gases, H₂(g), I₂(g), and HI(g), are introduced into a 3.0 L container that is heated to 600°C. According to the information above, which of the following will occur as the system approaches equilibrium?

More HI(g) will be produced because Q < Kc .

Step 1: H₂SeO₃(aq) ⇌ HSeO₃⁻(aq) + H+(aq) Ka₁ = 2.1 × 10⁻³ Step 2: HSeO³⁻(aq) ⇌ SeO₃²⁻(aq) + H+(aq) Ka₂ = 5.3 × 10⁻⁹ The step-wise dissociation of selenous acid, H₂SeO₃(aq), is represented by the equations above. Which of the following best helps explain why the value of Ka₂ is so much smaller than the value of Ka₁?

Removing the first H+ from H₂SeO₃(aq) requires less energy than removing the second H⁺, because the second H⁺ is removed from a negatively charged species.

The masses of carbon and hydrogen in samples of four pure hydrocarbons are given above. The hydrocarbon in which sample has the same empirical formula as propene, C3H6 ?

Sample B

The mass of the Cu(s) produced in step 3 was slightly more than the mass predicted from the 3.8 g of Cu₃(PO₄)₂(s) recovered from step 1. Which of the following could account for the discrepancy in the yield of Cu(s) from step 3 ?

Some unreacted Zn(s) was mixed in with the Cu(s).

Which of the following experimental techniques will allow the most accurate determination of the concentration of NO₂(g) at equilibrium?

Spectrophotometry

Ion Ionic Radius (pm) Cl⁻ 181 I⁻ 216 S²⁻ 184 Te²⁻ 221 Based on Coulomb's law and the information in the table above, which of the following anions is most likely to have the strongest interactions with nearby water molecules in an aqueous solution?

S²⁻

Which of the following correctly compares periodic properties of two elements and provides an accurate explanation for that difference?

The atomic radius of Cl is smaller than that of S because Cl has a larger nuclear charge than S does.

Which of the following can be inferred from the diagram above that shows the dependence of potential energy on the internuclear distance between two atoms?

The atoms form a bond with a bond length of 75pm.

A sealed 10.0L flask at 400K contains equimolar amounts of ethane and propanol in gaseous form. Which of the following statements concerning the average molecular speed of ethane and propanol is true?

The average molecular speed of ethane is greater than the average molecular speed of propanol.

Which of the following best explains why the combustion reactions represented in the table are exothermic?

The energy required to break the bonds in the reactants is less than the energy released in forming the bonds in the products.

Which of the following best helps to explain why Na(s) is more reactive with water than Mg(s) is?

The first ionization energy of Na is less than that of Mg.

A mixture of two gases, 0.01mol of C4H10(g) and 0.065mol of O2(g), is pumped into a cylinder with a movable piston, as shown above. The mixture, originally at 200°C and 1.0atm, is sparked and the reaction represented below occurs. 2C4H10(g)+13O2(g)→8CO2(g)+10H2O(g) Which of the following is true after the product gases return to the original temperature and pressure, and why will the change occur? (Assume all gases behave ideally.)

The piston will be higher than its original position, because the cylinder will contain a greater number of gas molecules.

The structural formulas for two isomers of 1,2−dichloroethene are shown above. Which of the two liquids has the higher equilibrium vapor pressure at 20°C, and why?

The trans-isomer, because it has only London dispersion forces, whereas the cis-isomer also has dipole-dipole interactions

Which of the following modifications will increase the rate of the reaction the most?

Using eggshells that are more finely powdered than those used in the original experiment

Ionization Energy (kJ/mol) First 730 Second 1450 Third 7700 Fourth 10,500 The ionization energies of an unknown element, X, are listed in the table above. Which of the following is the most likely empirical formula of a compound formed from element X and phosphorus, P ?

X3P2

The amount of H₂(g) present in a reaction mixture at equilibrium can be maximized by

increasing the temperature and decreasing the pressure by increasing the volume

In an experiment, 30.0g of ethane and 30.0g of propanol are placed in separate reaction vessels. Each compound undergoes complete combustion with excess O2(g). Which of the following best compares the quantity of heat released in each combustion reaction?

qethane > qpropanol

A student observes that the equilibrium constant for a reaction is greater than 1.0 at temperatures below 500K but less than 1.0 at temperatures above 500K. What can the student conclude about the values of ΔH° and ΔS° for the reaction? (Assume that ΔH° and ΔS° are independent of temperature.)

ΔH°<0 and ΔS°<0

Based on the values of ΔG° for the three reactions represented above, what is the value of ΔG° for the reaction represented below? 4NH₃(g) + 8O₂(g) → 4HNO₃(aq) + 4H₂O(l)

−1320 kJ/molrxn

AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq) In an experiment a student mixes a 50.0 mL sample of 0.100 M AgNO3(aq) with a 50.0 mL sample of 0.100 M NaCl(aq) at 20.0°C in a coffee-cup calorimeter. Which of the following is the enthalpy change of the precipitation reaction represented above if the final temperature of the mixture is 21.0°C? (Assume that the total mass of the mixture is 100. g and that the specific heat capacity of the mixture is 4.2 J/(g⋅°C).)

−84 kJ/molrxn

Based on the information in the table above, which of the compounds has the highest boiling point, and why?

(D) Propanoic acid, because it can form intermolecular hydrogen bonds

Three substances were studied in the laboratory, and the data in the table above were collected. Based on the data, which of the following shows the type of bonding in each substance?

(D) X: Network covalent Y: Metallic Z: Ionic

After a certain pesticide compound is applied to crops, its decomposition is a first-order reaction with a half-life of 5656 days. What is the rate constant, kk, for the decomposition reaction?

0.012 day^−1

CaF2(s) ⇄ Ca2+(aq) + 2F−(aq) Ksp=4.0×10−11 The concentration of F−(aq) in drinking water that is considered to be ideal for promoting dental health is 4.0×10−5M. Based on the information above, the maximum concentration of Ca2+(aq) that can be present in drinking water without lowering the concentration of F−(aq) below the ideal level is closest to

0.025M

The temperature of the CH3OH is increased from 300 K to 400 K to vaporize all the liquid, which increases the pressure in the vessel to 0.30 atm. The experiment is repeated under identical conditions but this time using half the mass of CH3OH that was used originally. What will be the pressure in the vessel at 400 K?

0.15 atm

Solution 0.1M HC2H3O2(aq) 0.1M HC2H3O2(aq) 0.1M KI(aq) 0.1M KI(aq) 0.1M CH3OH(aq)

0.1M KI(aq) because KI completely dissociates in water to produce ions.

Of the three solutions listed in the table above, which one, if any, has the greatest electrical conductivity and why?

0.1MKI(aq) because KI completely dissociates in water to produce ions.

The value of Kp for the evaporation of CH3OH(l) at 300 K is closest to

0.2

If 3.8 g of Cu₃(PO₄)₂(s) was recovered from step 1, what was the approximate [Cu²⁺] in the original solution? (The molar mass of Cu₃(PO₄)₂ is 381 g/mol.)

0.30 M

Another sample of eggshell reacts completely with 4.0mL of an HCl(aq) solution of unknown concentration. If the reaction produced 0.095atm of gas, the concentration of the HCl(aq) solution was at least

1.0M

The structural formula of the glycinium cation is shown above. Arrows indicate the pKa values for the labile protons in the molecule. What is the approximate H−O−C bond angle in the glycinium cation?

105°

The pH of a solution made by combining 150.0 mL of 0.10 M KOH(aq) with 50.0 mL of 0.20 M HBr(aq) is closest to which of the following?

12

A 0.0300 mol sample of NO₂(g) is placed in a rigid 1.00 L reaction vessel and allowed to reach equilibrium at a certain temperature. What is the value of Kc at this temperature if 0.00500 mol of N₂O₄(g) is present at equilibrium?

12.5

Ge(g)+2Cl2(g)⇄GeCl4(g) The value of the equilibrium constant for the reaction represented above is 1×10^10. What is the value of the equilibrium constant for the following reaction? 2GeCl4(g)⇄2Ge(g)+4Cl2(g)

1×10^-20

HNO 2(aq) ←→ H+(aq) + NO2 −(aq) K = 4.0 × 10−4 On the basis of the information above, what is the approximate percent ionization of HNO2 in a 1.0 M HNO2(aq) solution?

2.0%

When 70. g of Li₃N(s) (molar mass 35 g/mol) reacts with excess H₂(g), 8.0 g of LiH(s) is produced. The percent yield is closest to

25%