AP Chemistry Final Exam

Reaction 2 occurs when an excess of 6 M HCl(aq) solution is added to 100 mL of NaOCl(aq) of unknown concentration. If the reaction goes to completion and 0.010 mol of Cl2(g) is produced, then what was the molarity of the NaOCl (aq) solution?

0.10 M

Fe(s) + 2HCl(aq) -> FeCl2(aq) +H2(g) 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 above. When the reaction is complete at 273 K and 1.0 atom, which of the following is true?

0.22 L of H2 has been produced.

2H2O2(aq) -> 2H2O(l) + O2(g) E° = 0.55 V The equation and standard cell potential for the decomposition of H2O2(aq) in acidic solution at 25℃ is given above. The reduction half reactions for the process are listed below. O2(g) + 4H+(aq) + 4e- -> 2H2O(l) E° = 1.23 V O2(g) + 2H+(aq) + 2e- -> H2O2(aq) E° = ? 1) O2(g) + 2H+(aq) + 2e- -> H2O2(aq) What is the standard reduction potential for the half reaction represented above? 2) Which of the following is true for the decomposition of H2O2(aq)?

1) +0.68 V 2) ΔG° < 0 and Keq > 1

At 27 ℃, five identical rigid 2.0 L vessels are filled with N2(g) and sealed. Four of the five vessels also contain a 0.050 mol sample of NaHCO3 (S), NaBr(s), Cu(s), or I2(s), as shown in the diagram above. The volume taken up by the solids is negligible, and the initial pressure of N2(g) in each vessel is 720 mmHg. All four vessels are heated to 127 ℃ and allowed to reach a constant pressure. 1) At 127 ℃, the pressure in vessel 1 is found to be higher than that in vessel 2. Which of the following reactions best accounts for the observation? 2) At 127 ℃, the entire sample of I2 is observed to have vaporized. How does the mass of vessel 5 at 127℃ compare to its mass at 27℃? 3) The gas particles in vessel 3 at 27 ℃ are represented in the diagram above. The lengths of the arrows represent the speeds of the particles. Which of the following diagrams best represents the particles which vessel 3 is heated to 127℃?

1) 2NaHCO3(s) -> Na2CO3(s) + CO2(g) +H2O(g) 2) The mass is the same since the number of each type of atom in the vessel is constant. 3) Refer to 2015 question 9

(Refer to questions 37-39 on the 2016 test to see full background info for problems) 1) Two trials are run, using excess water. In the first trial, 7.8g of Na2O2(s) (molar mass 78g /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). The Na2O2 and S react as completely as possible. Both trials yield the same amount of SO2(aq). Which of the following identifies the limiting reactant and the heat released, q, for the two trials at 298 K? 2) Atoms of which element are reduced in the reaction? 3) Which of the following statements about the thermodynamic favorability of the reaction ar 298 K is correct?

1) Na2O2, 30kJ 2) O in Na2O2; each atom gains one electron 3) It is thermodynamically favorable and is driven by ΔH° only.

CH2OH(g) -> CO(g) +2H2(g) ΔH° = +91 kJ/mol The reaction represented above goes essentially to completion. The reaction takes place in a rigid, insulated vessel that is initially at 600 K. 1) What happens to the temperature of the contents of the vessel as the reaction occurs? 2) A sample of CH3OH(g) is placed in the previously evacuated vessel with a pressure of P1 at 600K. What is the final pressure in the vessel after the reaction is complete and the contents of the vessel are returned to 600 K? 3) What can be inferred about ΔS° for the reaction at 600K? 4) Which of the following statements about the bonds in the reactants and products is most accurate?

1) The temperature must decrease because the reaction is endothermic 2) 3P1 3) It must be positive since ΔG° is negative and ΔH° is positive. 4) The sum of the bond enthalpies of the bonds in the reactant is greater than the sum of the bond enthalpies of the bonds in the products

The O2(g) produced from the decomposition of the 1.0 L sample of H2O2(aq) is collected in a previously evacuated 10.0 L flask at 300 K. What is the approximate pressure in the flask after 400 s?

1.2 atm

Which of the following is the balanced net ionic equation for the reaction between Li(s) and water?

2Li(aq) + 2H2O(l) -> 2 Li+(aq) +2OH-(aq) +H2(g)

On the basis of the pH curve, the pKa value of the acid is closest to

5

A hot iron ball is dropped into a 200. g sample of water initially at 50 ℃. If 8.4 kJ of heat is transferred from the ball to the water, what is the final temperature fo the water? (The specific heat of water is 4.2 J / (g ℃).)

60 ℃

The acid dissociation constants of HC3H5O3(aq) and CH3NH3+(aq) are given in the table above. Which of the following mixtures is a buffer with a pH of approximately 3?

A mixture of 100 mL of 0.1 M HC3H5O3 and 50 mL of 0.1 NaOH

A student performs an acid-base titration and plots the experimental results in the graph above. Which of the following statements best explains the experimental findings?

A weak acid was titrated with a strong base, as evidenced by the equivalence point at pH >7

An acetate buffer solution is prepared by combining 50 mL of 0.20 M acetic acid, HC2H3O2(aq), and 50 mL 0f 0.20 M sodium acetate, NaC2H3O2(aq). A 5.0 mL sample of 0.10 M NaOH(aq) is added to the buffer solution. Which of the following is a correct pairing of the acetate species present in greater concentration and of the pH solution after the NaOH is added? (the pKa of acetic acid is 4.7)

Acetate Species: C2H3O2 - pH: >4.7

C2H4(g) + H2(g) -> C2H6(g) Which of the following will most likely increase the rate of the reaction represented above?

Adding a heterogenous catalyst to the reaction system

To gravimetrically analyze the silver content of a piece of jewelry made from an alloy of Ag and Cu a student dissolves a small preweighed sample in hno3, ag+ (aq) and cu2+(aq) ions form in the solution. Which of the following should be the next step in the analytical process?

Adding a solution containing an anion that forms an insoluble salt with only one of the metal ions.

N2 (g) + 3H2 g <> 2NH3(g) ΔH < 0 NH3(g) was synthesized at 200℃ in the presence of a powdered Os(s) catalyst, leading to the equilibrium system represented above. Which of the following changes would result in more NH3(g) in the mixture after equilibrium is reestablished?

Adding some N2(g)

Which of the following accounts for the observation that the pH of pure water at 37 ℃ is 6.8?

At 37 ℃ the auto-ionization constant for water, Kw, is larger than it is at 25 ℃

Which of the following best help explain why an increase in temperature increases the rate of a chemical reaction?

At higher temperatures, high energy collisions happen more frequently.

The first five ionization energies of a second period element are listed in the table above. Which of the following correctly identifies the element and best explains the data in the table

B (boron), because it has three valence electrons

If equal masses of the following compounds undergo complete combustion, which will yield the greatest mass of CO2?

Benzene, C6H6

The pH of a 0.01 M HNO2(aq) solution is in which of the following ranges? (For HNO2(aq), Ka + 4 E-4)

Between 2 and 3

The proposed mechanism can be written in a more general form, as shown above. Species other than Cl can also decompose O3 through the same mechanism. Which of the following chemical species is most likely to decompose O3 in the upper atmosphere through the above mechanism?

Br

A 23.0 g sample of a compound contains 12.9 g of C, 3.0 g of H, and 8.0 g of O. Which of the following is the empirical formula of the compound?

C2H6O

The molecular formula and molar mass of two straight chain hydrocarbons are listed in the table above. Based on the information in the table, which compound has the higher boiling point and why is that compound's boiling point higher?

C4H10, because it has more electrons, resulting in greater polarizability and stronger dispersion forces.

Which of the following is least soluble in water?

CCl4 (refer to question 17 on the 2016 test)

In which of the following liquids do the intermolecular forces include dipole-dipole forces?

CH2F2(l)

Element: Electronegativity: C 2.5 F 4.0 Si 1.8 S 2.5 Cl 3.0 H 2.1 On the basis of the information above, which of the following arranges the binary compounds in order of increasing bond polarity?

CH4 < SiCl4 < SF4

A sample of a compound that contains only the elements C, H, and N is completely burned in O2 to produce 44.0 g of CO2, 45g of H2O, and some NO2. A possible empirical formula of the compound is

CH5N

Compound: Molar mass: Boiling Point: CS2(l): 76: 46.5 CCl4(l): 154: 76.7 Based on the information in the table above, which liquid, CS2 (l) or CCl4(l), has the higher equilibrium vapor pressure at 25℃, and why?

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

(underwater fireworks) Ca(OH)2 (s) precipitates when a 1.0 g sample of CaC2(s) is added to 1.0 L of distilled water at room temperature. If a 0.064 g sample of CaC2(s) (molar mass 64 g/mol) is used instead and all of it reacts, which of the following will occur and why? (The value of Ksp for Ca(OH)s is 8.0 X 10-8)]

Ca(OH)2 will not precipitate because Q < Ksp

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

The exothermic dissolution of Mg(OH)2 (s) in water is represented by the equation above. The Ksp of Mg(OH)2 is 1.8 x 10⁻¹¹. Which of the following changes will increase the solubility of Mg(OH)2 in an aqueous solution?

Decreasing the pH

The dissociation of the weak acid HF in water is represented by the equation above. Adding a 1.0 mL sample of which of the following would increase the percent ionization of HF(aq) in 10 mL of a solution of 1.0 M HF?

Distilled water

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

Which of the following best depicts an alloy of Ni and B? (I couldn't upload a picture, but this is question 4 from the 2015 exam. Answer: A)

Explanation of answer: Alloys are made when two metals are melted together and re-solidified. Completely random arrangement of atoms, but generally, one of the element's atoms will fall into the interstitial places between the solid form of the other element

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

F2 < O2 < N2

Assume the bond enthalpies of the oxygen - hydrogen bonds in H2O are not significantly different from those in H2O2. Based on the value of ΔH° of the reaction, which of the following could be the bond enthalpies for the bonds broken and formed in the reaction?

H2O2: 150 O2: 500 O-H: 500

2 H2S(g) + CH4(g) <--> CS2(g) + 4H2(g) Kc = 3.4 E-4 A 0.10 mol sample of each of the four species in the reaction represented above is injected into a rigid, previously evacuated 1.0 L container. Which of the following species will have the high concentration when the system reaches equilibrium?

H2S(g)

The Lewis electron-dot diagrams of the HClO3 molecule and the HClO2 molecule are shown above at the left and right, respectively. Which of the following statements identified the stronger acid and correctly identifies a factor that contributes to its being the stronger acid?

HClO3(aq) is the stronger acid because the additional electronegative oxygen atom on the chlorine atom stabilizes the conjugate base.

HX(aq) + Y-(aq) <--> HY(aq) + X-(aq) Based on the information above, which of the following is the strongest acid?

HX(aq)

A 0.5 mole sample of He(g) and a 0.5 mole sample of Ne(g) are placed separately in two 10.0 L rigid containers at 25 ℃. Each container has a pinhole opening. Which of the gases, He(g) or Ne(g), will escape faster through the pinhole and why?

He(g) will escape faster because the He(g) atoms are moving at a higher average speed than the Ne(g) atoms.

Which of the following is the strongest type of interaction that occurs between the atoms within the circled areas of the two molecules represented above? (The picture shows H and O circled as well as H and N)

Hydrogen bond

A sample of a hard, solid binary compound at room temperature did not conduct electricity as a pure solid but became conductive when dissolved in water. Which of the following types of interactions is most likely found between the particles in the substance?

Ionic bonds

At room temperature I2(g) is a molecular solid. Which of the following provides a characteristic of I2(s) with a correct explanation?

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

The reaction system represented above is at equilibrium. Which of the following will decrease the amount of CaO(s) in the system?

Lowering the temperature of the system

The lattice energy of a salt is related to the energy required to separate the ions. For which of the following pairs of ions is the energy that is required to separate the ions the largest? (Assume that the distance between the ions in each pair is equal to the sum of the ionic radii.)

Mg2+ (g) and O2- (g)

2 NO2(g) +F2(g) -> 2NO2F(g) The rate law for the reaction represented by the equation above 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)

Ion: Li+, Ionic Radius: 60 Ion: Ca2+ Ionic Radius: 99 Ion: Na+ Ionic Radius: 95 Ion: In3+ Ionic radius: 81 Based on Coulomb's law and the information in the table above, which of the following cations is most likely to have the weakest interaction with an adjacent water molecule in an aqueous solution?

Na+

Compound Ksp at 298 K Ag2SO4 1 E-5 PbSO4 1 E-8 A 1.0 L solution of AgNO3(aq) and Pb(NO3)2(aq) has an Ag+ concentration of 0.020 M and a Pb2+ concentration of 0.001 M. A 0.001 mol sample of K2SO4(s) is added to the solution. Based on the information in the table above, which of the following will occur? (Assume that the volume change of the solution is negligible.)

Only PbSO4(s) will precipitate

The decomposition of H2O2(aq) is represented by the equation above. A student monitored the decomposition of a 1.0 L sample of H2O2(aq) at a constant temperature of 300 K and recorded the concentration of H2O2 as a function of time. The results are given in the table below. Which of the following identifies the element(s) being oxidized and reduced in teh reaction?

Oxygen is both oxidized and reduced

A solution is prepared by mixing 50 mL of 1 M NaH2PO4 with 50 mL of 1 M Na2HPO4. On the basis of the information above, which of the following species is present in the solution at the lowest concentration?

PO43-

Compound: Ksp: PbCl2 1.2 E-5 CuCl 1.6 E-7 AgCl 1.8 E-10 Hg2Cl2 1.4 E-18 Based on the Ksp values in the table above, a saturated solution of which of the following compounds has the highest [Cl-]?

PbCl2

which of the following reaction energy profiles best corresponds to the proposed mechanism?

Refer to 2015 question 43

The diagram above represents the absorption spectrum for a pure molecular substance. Which of the following correctly indicates the type of transition observed for the substance in each of the regions of the absorption spectrum?

Region X: Electronic transition Region Y: Molecular vibration Region Z: Molecular rotation

Acid dissociation constants of two acids are listed in the table above. A 20 mL sample of a 0.10 mL sample of a 0.10 M solution of each acid is titrated to the equivalence point with 20 mL of 0.10 M NaOH. Which of the following is a true statement about the pH of the solutions at the equivalence point?

Solution 1 has a higher pH at the equivalence point because CH3CO2H has a stronger conjugate base.

To maximize the yield in a certain manufacturing process, a solution of a weak monoprotic acid that has a concentration between 0.20 M and 0.30 M is required. Four 100. mL samples of the weak acid at different concentrations are each titrated with 0.20 M NaOH(aq). The volume of NaOH needed to reach the end point for each sample is given in the table above. Which solution is the most suitable to maximize the yield?

Solution C (115)

What will be the effect on the amount of gas produced if the experiment is repeated using 0.35g of K(s) instead of 0.35 g of Li(s)

Some gas will be produced but less than the amount of gas produced with Li(S)

Benzene, C6H6, has the structure shown above. Considering the observation that benzene is only sparingly soluble in water, which of the following best described the intermolecular forces of attraction between water and benzene?

The are dipole-induced dipole and London dispersion interactions between water and benzene.

The mass spectrum of element X is presented in the diagram above. Based on the spectrum, which of the following can be concluded about element X? (I couldn't upload a picture from the exam, but this is question 3 from the 2015 test)

The atomic mass of X is between 90 and 92

The potential energy of a system of two atoms as a function of the internuclear distance is shown in the diagram above. Which of the following is true regarding the forces between the atoms when their internuclear distance is x?

The attractive and repulsive forces are balanced, so the atoms will maintain an average internuclear distance x.

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 colume of the container.

A 1.0 g sample of a cashew was burned in a calorimeter containing 1000. g of water, and the temperature of the water changed from 20.0°C to 25.0°C. In another experiment, a 3.0 g sample of a marshmallow was burned in a calorimeter containing 2000. g of water and the temperature of the water changed from 25.0°C to 30.0°C. Based on the data, which of the following can be concluded about the energy content of 1.0 g of each of the two substances.

The combustion of 1.0 g of cashew releases more energy than the combustion of 1.0 g of marshmallow.

X(g) -> X+(g) + e- IE1 = 740 kj/mol X+(g) -> X2+(g) + e- IE2 = 1450 kj/mol X2+(g) -> X3+(g) + e- IE3 = 7730 kj/mol For element X represented above, which of the following is the most likely explanation for the large difference between the second and third ionization energies?

The electron removed during the third ionization is, on average, much closer to the nucleus than the first electrons removed were.

AgNO3(aq) + NaCl(aq) -> AgCl(s) +NaNO3(aq) A student performed an analysis to determine the amount of AgNO3(aq) in a solution. Excess NaCl(aq) was added to the solution, and the Ag+(aq) precipitated as AgCl(s). The precipitate was collected by gravity filtration and dried in an over. Three trials were performed, and in each case, according to the instructor, the mass of the precipitate recovered was 5 percent higher than the actual mass of AgCl(s) that should have formed. Which of the following could account for the error?

The precipitate was not rinsed with deionized water before drying.

The reaction between NO(g) and O2(g) to produce NO2(g) in a rigid reaction vessel is represented in the diagram above. The pressure inside the container is recorded using a pressure gauge. Which of the following statements correctly predicts the change in pressure as the reaction goes to completion at constant temperature, and provided the correct explanation?

The pressure will decrease because there are fewer molecules of product than of reactants.

Two samples of Mg(s) of equal mass were placed in equal amounts of HCl(aq) contained in two separate reaction vessels. Particle representations of the mixing of Mg(s) and HCl(aq) in the two reaction vessels are shown in figure 1 and figure 2 above. Water molecules are not included in the particle representations. Which of the reactions will initially proceed faster and why?

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

Which of the following statements is a correct interpretation of the data regarding how the order of the reaction can be determined?

The reaction is first order if the plot of ln[H2O2] versus time is a straight line

A certain gas, XY(g), decomposes as represented in the equation above. A sample of each of the three gases is put in a previously evacuated container. The initial partial pressures of the gases are shown in the table below. The temperature of the reaction mixture is held constant. In which direction will the reaction proceed?

The reaction will form more reactant.

The heating curve for a sample of pure ethanol is provided above. The temperature was recorded as a 50.0 g sample of solid ethanol was heated at a constant rate. Which of the following explains why the slope of segment T is greater than the slope of segment R?

The specific heat capacity of the gaseous ethanol is less than the specific heat capacity of liquid ethanol.

Which of the following changes will most likely increase the rate of reaction between Li(s) and water?

Using a 0.35 g sample of Li(s) cut into small pieces

Ionization Energy (kJ/mol) First 577 Second 1,816 Third 2,745 Fourth 11,577 Fifth 14,482 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

In a paper chromatography experiment, a sample of a pigment is separated into two components, X and Y, as shown in the figure above. The surface of the paper is moderately polar. What can be concluded about X and Y based on the experimental results?

Y is more polar than X

In order to determine the order of the reaction represented above, the initial rate of formation of XY2 is measured using different initial values of [X] and [Y]. The results of the experiment are shown in the table below. In trial 2 which of the reactants would be consumed more rapidly, and why?

Y, because the rate of disappearance will be double that of X

A solution of a salt of a weak acid HY is added to a solution of another weak acid HX. Based on the information given above, which of the following species is the strongest base?

Y- (aq)

When Reaction 3 occurs, does the hybridization of the carbon atoms change?

Yes; it changes from sp to sp2

Acid Concentration pH X 0.005 M 2.3 Y 2.0 2.8 Z 3.0 2.8 Which of the following correctly ranks the three monoprotic acids listed in the table above from the weakest to the strongest?

Z < Y < X

CO (g) + H2O(g) <--> CO2(g) +H2(g) Kc = 1.5 E3 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. Which of the following is true at equilibrium?

[CO2] > [CO]

A 1.0 mole sample of X(g) and a 1.0 mol sample of Q(g) are introduced into an evacuated, rigid 10.L container and allowed to reach equilibrium at 50℃ according to the equation above. At equilibrium, which of the following is true about the concentrations of the gases?

[R]=[Z] > [Q]

When free Cl(g) atoms encounter O3(g) molecules in the upper atmosphere, the following reaction mechanism is proposed to occur. Which of the following rate laws for the overall reaction corresponds to the proposed mechanism?

rate = k[Cl][O3]

The reaction is thermodynamically favorable. The signs of ΔG° and ΔS° for the reaction are which of the following?

ΔG°: negative ΔS° : positive

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

ΔH°: Positive ΔS°: Positive