AP CHEM MCQ

CH3OH vaporization- 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

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

0.2

Cu Recovery- 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

2 NO2(g) ⇄ N2O4(g) dark brown colorless The dimerization of NO2(g) , an exothermic process, is represented by the equation above. 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

H2 storage- Because pure H2 is a hazardous substance, safer and more cost effective techniques to store it as a solid for shipping purposes have been developed. One such method is the reaction represented above, which occurs at 200°C. 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%

Which of the following particle diagrams best represents the products when four molecules of H2O2(l) decompose into water and oxygen gas at room temperature?

4 compounds, 2 diatomic Oxygen

CH3OH vaporization- 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.

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

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

C2H8O2

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 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

H2 storage- Because pure H2 is a hazardous substance, safer and more cost effective techniques to store it as a solid for shipping purposes have been developed. One such method is the reaction represented above, which occurs at 200°C. 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)

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 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 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

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.

NO(g) + NO3(g) → 2 NO2(g) The reaction between NO(g) and NO3(g) is represented by the equation above. Which of the following orientations of collision between NO(g) and NO3(g) is most likely to be effective?

Oo and oOoo

A student studied the kinetics of the reaction represented above by measuring the concentration of the reactant, X, over time. The data are plotted in the graph below. 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.

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

Propanoic acid, because it can form intermolecular hydrogen bonds

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? Responses

Rate = k[NOBr]2

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

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?

Substance X- network covalent Substance Y- metallic Substance Z- ionic

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.

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 50.0 g sample of Fe at 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.

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.

Cu Recovery- 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 ?

Too much Na3PO4(aq) was added to the original Cu2+(aq) solution.

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

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

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

brF diagram

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

Which of the following shows the relationship between K1 and K2 in the reactions represented above?

k2= 1/(k1^2)

CH3OH vaporization- 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 of the larger number of hydrogen bonds among C2H5OH molecules

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-

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