2016 AP Chemistry Exam Review

Flashcards from the 2016 AP Chemistry Exam

What type of intermolecular forces are present in CH2F2(l)?

Dipole-dipole forces

How does increasing temperature affect the rate of a chemical reaction?

High-energy collisions happen more frequently.

What type of bonds are most likely found in a hard, solid binary compound that does not conduct electricity as a pure solid but becomes highly conductive when dissolved in water?

Ionic bonds

For the reaction N2(g) + 3 H2(g)  2 NH3(g) H < 0, what change would result in more NH3(g) after equilibrium is reestablished?

Adding some N2(g)

Which of the following arranges the molecules N2, O2, and F2 in order of their bond enthalpies, from least to greatest?

F2 < O2 < N2

Based on Coulomb’s law, which cation (Li+, Na+, Ca2+, In3+) is most likely to have the weakest interaction with an adjacent water molecule in an aqueous solution?

Na+

Based on electronegativity, arrange CH4, SiCl4, and SF4 in order of increasing bond polarity.

CH4 < SiCl4 < SF4

For element X with ionization energies IE1 = 740 kJ/mol, IE2 = 1450 kJ/mol, and IE3 = 7730 kJ/mol, what explains the large difference between the second and third ionization energies?

The electron removed during the third ionization is much closer to the nucleus than the first two electrons.

What best explains the experimental findings of a titration plotted on a graph with the equivalence point at pH > 7?

A weak acid was titrated with a strong base.

In which reaction (Figure 1 or Figure 2) will initially proceed faster and why when two samples of Mg(s) of equal mass were placed in equal amounts of HCl(aq)?

The reaction in Figure 2, because more Mg atoms are exposed to HCl(aq) in Figure 2 than in Figure 1

What is the empirical formula of a compound containing 12.0 g of C, 3.0 g of H, and 8.0 g of O in a 23.0 g sample?

C2H6O

Based on Ksp values (PbCl2: 1.2 × 105, CuCl: 1.6 × 107, AgCl: 1.8 × 1010, Hg2Cl2: 1.4 × 1018), a saturated solution of which compound has the highest [Cl]?

PbCl2

E° = 0.55 V Given 2 H2O2(aq)  2 H2O(l) + O2(g). What is the Standard Reduction potential for the half reaction O2(g) + 2 H+(aq) + 2 e  H2O2(aq) if O2(g) + 4 H+(aq) + 4 e  2 H2O(l) E = 1.23 V

+0.68 V

Given 2 H2O2(aq)  2 H2O(l) + O2(g) with E° = 0.55 V. Which of the following is true for the decomposition of H2O2(aq)?

DG° < 0 and Keq > 1

What will most likely increase the rate of the reaction C2H4(g) + H2(g)  C2H6(g)?

Adding a heterogeneous catalyst to the reaction system

Which of the following molecules is least soluble in water?

The molecule with the most carbons to the fewest OH bonds.

What are some of I2(s) characteristic with a correct explanation?

It is not a good conductor of electricity because its valence electrons are localized in bonding and nonbonding pairs.

Based on the information in the table, which liquid, CS2(l) or CCl4(l), has the higher equilibrium vapor pressure at 25C, and why?

CS2(l), because it has weaker London dispersion forces

Based on the information given above, which of the following is the strongest acid from HX(aq) + Y(aq)  HY(aq) + X(aq) Keq > 1

HX(aq)

What could account for the error if the mass of precipitate recovered was 5 percent higher than the actual mass of AgCl(s) that should have formed from the reaction of a student performed an analysis to determine the amount of AgNO3(aq) in a solution AgNO3(aq) + NaCl(aq)?

The precipitate was not rinsed with deionized water before drying.

At the point labeled R on the pH curve, which of the following ions are present in the reaction mixture at a concentration greater than 0.01 M when NaOH(aq) + HCl(aq)  NaCl(aq) + H2O(l). has taken place?

Na+ and Cl only

One student titrated the NaOH(aq) with 1.0 M HCl(aq) instead of 0.10 M HCl(aq). How would the student’s titration curve differ from the original curve?

The pH far beyond the equivalence point would be lower than in the original curve.

A student conducted an experiment to determine DHrxnfor the reaction between HCl(aq) and NaOH(aq). The student ran two trials using the volumes of HCl(aq) and NaOH(aq) indicated in the table above, and determined the amount of heat released. Which of the following best explains the relationship between X and Y?

Y = 2X, because the volume of HCl(aq) used in trial 2 is twice the volume used in trial 1.

A student mixes a 10.0 mL sample of 1.0 M NaOH(aq) with a 10.0 mL sample of 1.0 M HCl(aq) in a polystyrene container. The temperature of the solutions before mixing was 20.0°C. If the final temperature of the mixture is 26.0°C, what is the experimental value of DHrxn?

25 kJ/molrxn

The rate law for the reaction 2 NO2(g) + F2(g)  2 NO2F(g) is rate = k [NO2][F2]. Which of the following could be the first elementary step of a two-step mechanism for the reaction if the first step is slow and the second step is fast?

NO2(g) + F2(g)  NO2F(g) + F(g)

Which of the following Lewis electron-dot diagrams represents the molecule that contains the smallest bond angle?

The one with 4 bonded domains and 2 lone pairs

A mixture containing equal numbers of moles of ethyl acetate and butyl acetate was separated using distillation. Based on the diagrams shown above, which of the following identifies the substance that would be initially present in higher concentration in the distillate and correctly explains why that occurs?

Ethyl acetate, because it has a shorter carbon chain and weaker London dispersion forces

Approximately how long did it take for 75 percent of the initial amount of C25H30N3 +(aq) to react when C25H30N3 +(aq) + OH(aq)  C25H30N3OH(aq) takes place?

120 s

What would be the effect on the reaction rate if the solution of C25H30N3 +(aq) is diluted by a factor of two when C25H30N3 +(aq) + OH(aq)  C25H30N3OH(aq) takes place?

It would be lower.

To choose a wavelength to analyze the progress of the reaction C25H30N3 +(aq) + OH(aq)  C25H30N3OH(aq), a student records the absorbance spectra of both C25H30N3 +(aq) and C25H30N3OH(aq) in the range of 200-800 nm. To measure [C25H30N3 +] with the greatest sensitivity as the reaction progresses what indicates the best wavelength setting and explains why it is best?

590 nm, because only the violet form of the molecule will absorb significantly at this wavelength

A 2.0 mol sample of CO(g) and a 2.0 mol sample of H2O(g) are introduced into a previously evacuated 100. L rigid container, and the temperature is held constant as the reaction represented above reaches equilibrium. What is true at equilibrium given CO(g) + H2O(g)  CO2(g) + H2(g) Kc = 1.5  103?

[H2O] < [CO] and [CO2] > [H2]

A 1.0 L solution of AgNO3(aq) and Pb(NO3)2(aq) has a Ag+ concentration of 0.020 M and a Pb2+ concentration of 0.0010 M. A 0.0010 mol sample of K2SO4(s) is added to the solution. Based on the information in the table above, which of the following will occur?

Only PbSO4(s) will precipitate.

The pH of a 0.01 M HNO2(aq) solution is in which of the following ranges? (For HNO2(aq), Ka = 4.0 × 104)

Between 2 and 3

The photoelectron spectra of the 1s electrons of two isoelectronic species, Ca2+ and Ar are shown above. Which of the following correctly identifies the species associated with peak X and provides a valid justification?

Ca2+, because its nucleus has two more protons than the nucleus of Ar has

A vessel contains Ar(g) at a high pressure. Which of the following statements best helps to explain why the measured pressure is significantly greater than the pressure calculated using the ideal gas law?

The combined volume of the Ar atoms is too large to be negligible compared with the total volume of the container.

Two trials are run, using excess water with 2 Na2O2(s) + S(s) + 2 H2O(l)  4 NaOH(aq) + SO2(aq) DH298  = 610 kJ/molrxn. In the first trial, 7.8 g of Na2O2(s) (molar mass 78 g/mol) is mixed with 3.2 g of S(s). In the second trial, 7.8 g of Na2O2(s) is mixed with 6.4 g of S(s). Which of the following identifies the limiting reactant and the heat released, q, for the two trials at 298 K?

Na2O2, 61 kJ

Atoms of which element are reduced in the reaction? 2 Na2O2(s) + S(s) + 2 H2O(l)  4 NaOH(aq) + SO2(aq)

O in Na2O2; each atom gains one electron

Which of the following statements about the thermodynamic favorability of the reaction at 298 K is correct? 2 Na2O2(s) + S(s) + 2 H2O(l)  4 NaOH(aq) + SO2(aq)

It is thermodynamically favorable and is driven by DHonly.

Based on the bond energies shown in the table above, which of the following diagrams best represents the change in energy as the reaction represented below proceeds? H2(g) + Cl2(g)  2 HCl(g)

The reactants at a higher energy than the products since it is an exothermic reaction with more energy being released than absorbed.

Based on the ionization energies of element X given in the table above, which of the following is most likely the empirical formula of an oxide of element X?

X2O3

A 0.10 mol sample of each of the four species in the reaction 2 H2S(g) + CH4(g)  CS2(g) + 4 H2(g) is injected into a rigid, previously evacuated 1.0 L container. Which of the following species will have the highest concentration when the system reaches equilibrium?

H2S(g)

At 1.0 atm a sample of ice is heated to liquid water and then to water vapor. Which of the following lists the signs for the changes in enthalpy and entropy for the process corresponding to segment X, going from left to right?

Positive, Positive

CH3OH(g)  CO(g) + 2 H2(g) takes place. The reaction takes place in a rigid, insulated vessel that is initially at 600 K. What happens to the temperature of the contents of the vessel as the reaction occurs?

The temperature must decrease, because the reaction is endothermic.

A sample of CH3OH(g) is placed in the previously evacuated vessel with a pressure of P1 at 600 K. If CH3OH(g)  CO(g) + 2 H2(g) takes place and returns to 600K, what is the final pressure in the vessel after the reaction is complete?

3P1

CH3OH(g)  CO(g) + 2 H2(g) with H° = +91 kJ/molrxn . What can be inferred about S° for the reaction at 600 K?

It must be positive, since G° is negative and H° is positive.

CH3OH(g)  CO(g) + 2 H2(g). Which of the following statements about the bonds in the reactants and products is most accurate?

The sum of the bond enthalpies of the bonds in the reactant is less than the sum of the bond enthalpies of the bonds in the products.

Which of the following correctly ranks the three monoprotic acids listed in the table above from the weakest to the strongest?

X < Z < Y

Based on the information above and periodic trends, which of the following is the best hypothesis regarding the oxide(s) formed by Rb?

Rb will form Rb2O, Rb2O2, and RbO2.

When a student adds 30.0 mL of 1.00 M HCl to 0.56 g of powdered Fe, a reaction occurs according to the equation Fe(s) + 2 HCl(aq)  FeCl2(aq) + H2(g). When the reaction is complete at 273 K and 1.0 atm, which of the following is true?

HCl is in excess, and 0.020 mol of HCl remains unreacted.