AP Chem All Unit MCQs

X2O3

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?

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

In the reaction represented above, what mass of HF is produced by the reaction of 3.0 x 10 23 molecules of H2 with excess F2 ? (Assume the reaction goes to completion.)

20. g

Shown above are the equation representing the decomposition ofH202(l) and a table of bond enthalpies. On the basis of the information, which of the following is the enthalpy of decomposition of 2 mol of H202(l) ?

-203 kJ

According to the information above, what is the standard enthalpy of formation, △H°f for NH3(g) at 298 K ?

-46 kJ/mol

A 0.20 mol sample of MgC12(s) and a 0.10 mol sample of KCl(s) are dissolved in water and diluted to 500 mL. What is the concentration of Cl- in the solution?

1.0 M

Based on periodic trends and the data in the table above, which of the following are the most probable values of the atomic radius and the first ionization energy for potassium, respectively?

242 pm, 419 kJ/m01

For the reaction represented above, the initial rate of decrease in [X] was 2.8 x 10 -3 mol L -1 s -1. What was the initial rate of decrease in [Y] ?

5.6 x 10 -3 mol L -1 s -1

Under which of the following conditions of temperature and pressure will H2 gas be expected to behave most like an ideal gas?

500 K and 0.10 atm

A student prepares a solution by dissolving 60.00 g of glucose (molar mass 180.2 g mol -1) in enough distilled water to make 250.0 mL of solution. The molarity of the solution should be reported as

1.332M

If the oxygen isotope 20 O has a half-life of 15 seconds, what fraction of a sample of pure 20 O remains after 1.0 minute?

1/16

What is the approximate H — O — C bond angle in the glycinium cation?

105°

The pH of a solution prepared by the addition of 10. mL of 0.002 M KOH(aq) to 10. mL of distilled water is closest to

11

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

12

A flask contains 0.25 mole of S02(g), 0.50 mole ofCH4(g), and 0.50 mole of 02(g). The total-pressure Of the gases in the flask is 800 mm Hg. What is the partial pressure of the S02(g) in the flask?

160 mm Hg

Which of the following ground-state electron configurations represents the atom that has the lowest first-ionization energy?

1s2 2s2 2p6 3s1

The atomic mass of X is between 90 and 92.

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?

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

60°C

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?

A1, because of the large difference between the third and fourth ionization energies

Ag+(aq) + NH3(aq) →← Ag(Nh3)+(aq) Keq1 = 2.0 X 10 3 Ag(NH3)+(aq) + NH3(aq) →← Ag(NH3)2+(aq) Keq3 = 8.0 X 10 3 Equal volumes of 0.1 M AgN)O3(aq) and 2.0 MNH3(aq) are mixed and the reactions represented above occur. Which Ag species will have the highest concentration in the equilibrium system shown below, and why? Ag+(aq) + 2 NH3 →← Ag(Nh3)2+(aq). K eq3=?

Ag(NH3)2+(aq), because Keq3 = 1.6 x 10^7

The molecule with only one double bond

C2H4

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

CH2F2(l)

CS2(l) + 2H2O(l) + CO2(g) + 2H2S(g) △H° rxn= Which of the following combinations represents the individual reactions and the quantities needed to determine △H° for the overall reaction represented by the chemical equation above?

CS2(l) + 3 O2(g) → CO2(g) + 2 SO2(g) △H° = -1075kJ 2 H2O(l) + 2 SO2(g) → 2 H2S(g) + 3 O2(g) △H° = +1136 kJ

Which of the following substances has bonds with the greatest ionic character?

CaCl2

Which of the following lists the substances F2, HCI, and HF in order of increasing boiling point?

F2 < HCI < HF

2 H2S(g) + CH4(g) →← CS2(g) + 4 H2(g) Kc = 3.4 x 10 -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 highest concentration when the system

H2S(g)

A solution is prepared by adding 100 mL of 1.0 M HC2H3O2(aq) to 100 mL of 1.0 M NaC2H302(aq). The solution is stirred and its pH is measured to be 4.73. After 3 drops of 1.0 m HCL are added to the solution, the pH of the solution is measured and is still 4.73. Which of the following equations represents the chemical reaction that accounts for the fact that acid was added but there was no detectable change in pH?

H3O+(aq) + C2H3O2-(aq) → HC2H3O2(aq) + H2O(l)

Which of the following has the bonds arranged in order of decreasing polarity?

H—F > N—F > F—F

H2(g) + I2(g) →← 2HI(g) △H° >0 Which of the following changes to the equilibrium system represented above will increase the quantity of HI(g) in the equilibrium mixture? I. Adding H2(g) II. Increasing the temperature Ill. Decreasing the pressure

I and II only

1s2 2s2 2p6 3s2 3p6 Which of the following species has the electon configuration shown above?

K+

A compound contains 1.10 mol of K, 0.55 mol of Te, and 1.65 mol of O. What is the simplest formula of this compound?

K2Te03

1s2 2s2 2p6 3s2 3p3 Atoms of an element, X, have the electronic configuration shown above. The compound most likely formed with magnesium, Mg, is

Mg3X2

Has the largest bond-dissociation energy?

N2

On the basis of molecular structure and bond polarity, which of the following compounds is most likely to have the greatest solubility in water?

NH3

Which of the following mechanisms for the catalyzed reaction is consistent with the equation and diagram above?

O3(g) + NO(g) → NO2(g) + O2(g) slow NO2(g) + O(g) → NO(g) + O2(g) fast

The molecule that has trigonal pyramidal geometry

PH3

Which of the following rate laws for the overall reaction corresponds to the proposed mechanism?

Rate = k[Cl][O3]

Acid-dissociation constants of two acids are listed in the table one. A 20. mL sample of a 0.10 M solution of each acid is titrated to the equivalence point with 20. mL of 0.10 MNaOH. 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 the stronger conjugate base.

A 50.0 mL sample of an acid, HA, of unknown molarity is titrated, and the pH of the resulting solution is measured with a meter and graphed as a function of the volume of 0.100 MNaOH added.

T

3 O2(g) →← 2 O3(g). Kc = 1.8 X 10 -56 at 570 K For the system represented above, [02] and [03] initially are 0.150 mol/L and 2.5 mol/L respectively. Which of the following best predicts what will occur as the system approaches equilibrium at 570 K?

The amount of O3(g) will decrease, because Q > Kc

The volume of a sample of air in a cylinder with a movable piston is 2.0 L at a pressure Pl, as shown in the diagram above. The volume is increased to 5.0 L as the temperature is held constant. The pressure of the air in the cylinder is now P2. What effect do the volume and pressure changes have on the average kinetic energy of the molecules in the sample?

The average kinetic energy stays the same.

HF(aq) + H2O(l) →← H3O+(aq) + F-(aq). pKa = 3.20 at 25°C The acid ionization equilibrium for the weak acid HF is represented by the equation above. To prepare a buffer with a pH = 3.50, a student needs to mix 250. mL of 0.100 MHF and 250. mL of 0.100 M KF. If the student mistakenly mixes 250. mL of 0.0500 M HF and 250. mL of 0.0500 M KF, which of the following is the result of this error?

The buffer will have a lower capacity because of the smaller number of moles of HF and F ̄ available to react if an acid or base is added.

A 100 g sample of a metal was heated to 100°C and then quickly transferred to an insulated container holding 100 g of water at 22°C. The temperature of the water rose to reach a final temperature of 35°C. Which of the following can be concluded?

The metal temperature changed more than the water temperature did, but the metal lost the same amount of thermal energy as the water gained.

Which of the following best describes what happens to the substance between t4 and t5?

The molecules are leaving the liquid phase.

CO(g) + 2 H2(g) →← CH3OH(g) The synthesis of CH3OH(g) from CO(g) and H2(g) is represented by the equation above. The value of Kc for the reaction at 483 K is 14.5. A 1.0 mol sample ofCO(g) and a 1.0 mol sample of H2(g) are pumped into a rigid, previously evacuated 2.0 L reaction vessel at 483 K. Which of the following is true at equilibrium?

[H2] < [CO]

The decrease in the second ionization energy of alkali metals going down the group, as shown in the table above, can be best attributed to a decrease in the coulombic force of attraction due to

an increase in the average distance of the outermost electron from the nucleus

Li3N(s) + 2 H2(g) →← LiNH2(s) + 2 LiH(s) △H° = -192 kJ/mol rxn 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. The amount ofH2(g) present in a reaction mixture at equilibrium can be maximized by

increasing the temperature and decreasing the pressure by increasing the volume

A molecular solid coexists with its liquid phase at its melting point. The solid-liquid mixture is heated, but the temperature does not change while the solid is melting. The best explanation for this phenomenon is that the heat absorbed by the mixture

is used in overcoming the intermolecular attractions in the solid

Which ofthe values of △H° for a process in the table is (are) less than zero (i.e., indicate(s) an exothermic process)

y and z only

How much energy is required to melt 64 g of methane at 90 K? (The molar mass of methane is 16 g/mol.)

3.8 kJ

The photoelectron spectra of the Is electrons of two isoelectronic species, Ca 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

RbCl has a high boiling point. Which of the following compounds is also likely to have a high boiling point, and why?

CsCl, because its elements have very different electronegativities and it is an ionic compound.

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 identifies the stronger acid and correctly identifies a factor that contributes to its being the stronger acid?

HC1O3(aq) is the stronger acid because the additional electronegative oxygen atom on the chlorine atom stabilizes the conjugate base.

Before sp2 After sp3

In the reaction represented above, what is the hybridization of the C atoms before and after the reaction occurs?

Which of the following indicators is the best choice for this titration?

Indicator pH Range of Color Change Phenolphthalein 8.2 - 10.0

Based on the results of the paper chromatography experiment shown above, which of the following can be concluded about the dye?

It has a weaker attraction for the stationary phase that it has for the mobile phase.

LA3+ + CO32- →← LACO3+ Based on the information above, which of the following expressions represents the equilibrium constant, K, for the reaction represented by the equation below?

K=(k1)(kw)/(ka)

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)

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 was true for the system between time tl and time t2?

The rates of the forward and reverse reactions were equal.

An unknown acid is dissolved in 25 mL of water and titrated with 0.100 MNaOH. The results are shown in the titration curve above. Which of the following could be the unknown acid?

glycolic acid, pKa = 3.8

Compared to the equilibrium vapor pressure of CH30H(l) at 300 K, the equilibrium vapor pressure of C2H50H(l) at 300 K is

lower, because London dispersion forces among C2H50H molecules are greater than those among CH30H molecules

The value of Kw at 37°C is 2.4 X 10 -14. Which of the following statements about the pH and pOH of pure water at 37°C is correct?

pH = POH < 7 because water dissociates to a greater extent at 37°C than at 25°C.

CaF2(s) →← ca2+(aq) +2F-(aq). Ksp = 4.0 x 10 -11 The concentration of F ̄(aq) in drinking water that is considered to be ideal for promoting dental health is 4.0 X 10 -5 M. 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

COC12(g) →← CO(g) + C12(g) COC12(g) decomposes according to the equation above. When pure COC12(g) is injected into a rigid, previously evacuated flask at 690 K, the pressure in the flask is initially 1.0 atm. After the reaction reaches equilibrium at 690 K, the total pressure in the flask is 1.2 atm. What is the value of K for the reaction at 690 K?

0.050

What is the expected absorbance of a standard solution made by dissolving 0.0070 mol of NiCl2 • 6H20 in water to make 100. mL of solution?

0.45

Resonance is most commonly used to describe the bonding in molecules of which of the following?

03

At 25°C, aqueous solutions with a pH of 8 have a hydroxide ion concentration, [OH-], of

1 x 10 -6 M

What volume of 02(g) is required to react with excess CS2(l) to produce 4.0 L of C02(g)? (Assume all gases are measured at OOC and I atm.)

12L

HNO2(aq) →← H+(⍺q) + NO-2(aq)K⍺ = 4.0 X 10-4 On the basis of the information above, what is the approximate percent ionization of HNO2 in a 1.0 MHNO2(aq) solution?

2.0%

If the absorbance of the mixture is 0.20 at 453 nm, how many moles of Fe3+(aq) were present in the 100. mL sample? (Assume that any volume change due to adding the KSCN(s) is negligible.)

4 x 10-6 moles

The figure above represents three sealed 1.0 L vessels, each containing a different inert gas at 298 K. The pressure of Ar in the first vessel is 2.0 atm. The ratio of the numbers of Ar, Ne, and He atoms in the vessels is :6, respectively. After all the gases are combined in a previously evacuated 2.0 L vessel, what is the total pressure of the gases at 298 K?

4.5 atm

Based on the information above, what is the enthalpy change for the sublimation of iodine, represented below?

62 kJ/molrxn

According to the reaction represented above, about how many grams of aluminum (atomic mass 27 g) are necessary to produce 0.50 mol of hydrogen gas at 25°C and 1.00 atm?

9.0 g

In a one-person spacecraft, an astronaut exhales 880 g of C02(g) (molar mass 44 g/mol) per day. To prevent the buildup of C02(g) in the spacecraft, a device containing LiOH(s) is used to remove the C02(g), as represented by the equation above. What mass of LiOH(s) (molar mass 24 g/mol) is needed to react with all of the C02(g) produced by an astronaut in one day?

960 g

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.

N2(g) + 3 H2(g) →← 2 NH3(g) △H < 0 NH3(g) was synthesized at 200°C 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

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

At higher temperatures, high-energy collisions happen more frequently.

Which of the following best helps to explain why hexane has a higher boiling point than methanol has?

Hexane molecules have electron clouds that are larger than those of methanol molecules.

Which of the following compounds contains both ionic and covalent bonds? SO3 C2H5OH MgF2 H2S NH4Cl

NH4C1

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

The system represented by the equation above is allowed to establish equilibrium. The initial pressures of the substances are given in the table. Which of the following explains what the system will do as it approaches equilibrium?

Q=(80)2 / (10)2 (2.0)2 > Kp and equilibrium will be approached by consuming NOBr because the reverse reaction is faster then the forward reaction.

In an experiment, 30.0 g of ethane and 30.0 g of propanol are placed in separate reaction vessels. Each compound undergoes complete combustion with excess 02(g). Which of the following best compares the quantity of heat released in each combustion reaction?

Qethane > Qpropanol

The initial-rate data in the table above were obtained for the reaction represented below. What is the experimental rate law for the reaction? 2 NO(g) + 02(g) → N02(g)

Rate = k[NO][O2]2

The data in the table above were obtained for the reaction X + Y →Z. Which of the following is the rate law for the reaction?

Rate = k[Y]2

If a pure sample of an oxide of sulfur contains 40. percent sulfur and 60. percent oxygen by mass, then the empirical formula of the oxide is

SO3

The dissolution of an ionic solute in a polar solvent can be imagined as occurring in three steps, as shown in the figure above. In step 1, the separation between ions in the solute is greatly increased just as will occur when the solute dissolves in the polar solvent. In step 2, the polar solvent is expanded to make spaces that the ions will occupy. In the last step, the ions are inserted into the spaces in the polar solvent. Which of the following best describes the enthalpy change, △H, for each step?

Steps 1 and 2 are endothermic, and the final step is exothermic.

After completing an experiment to determine gravimetrically the percentage of water in a hydrate, a student reported a value of 38 percent. The correct value for the percentage of water in the hydrate is 51 percent. Which of the following is the most likely explanation for this difference?

The dehydrated sample absorbed moisture after heating.

Line B will move to the left because a larger fraction of the Y2 molecules will have the minimum energy to overcome the activation energy barrier will have the minimum energy to overcome the activation energy barrier.

The energy distribution profile (Curve C) for the Y2 molecules is shown in the graph above for the reaction X + Y2 → XY2 when it is done under certain experimental conditions. Line A represents the most probable energy of the Y2 molecules, and Line B represents the activation energy. Which of the following changes should be made to the graph to explain the increase in the rate of the reaction if the only change in experimental conditions is the addition of a catalyst?

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 ionizations of chloroacetic acid is less then that of Fluroacetic acid

Two samples of Mg(s) of equal mass were placed in equal amounts ofHCI(aq) contained in two separate reaction vessels. Particle representations of the mixing of Mg(s) and HCI(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 HCI(aq) in Figure 2 than in Figure 1

A 1.0 mol sample ofX(g) and a 1.0 mol sample of Q(g) are introduced into an evacuated, rigid 10.0 L container and allowed to reach equilibrium at 50°C according to the equation above. At equilibrium, which of the following is true about the concentrations of the gases?

[R] = [ Z] > [Q]

A reaction mechanism for the destruction of ozone, 03(g), is represented above. In the overall reaction, NO(g) is best described as

a catalyst

What is the hybridization of the carbon atoms in a molecule of ethyne, represented above?

sp

If the standard molar heats of formation of ammonia, NH3(g), and gaseous water, H20(g), are -46 kJ/mol and -242 kJ/mol, respectively, what is the value of AH°298 for the reaction represented above?

-1,270 kJ/molrxn

If 0.40 mol of H2 and 0.15 mol of 02 were to react as completely as possible to produce H2O, what mass of reactant would remain?

0.20 g of H2

When a student adds 30.0 mL of I .00 MHCIto 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 atm, which of the following is true?

0.22 L of H2 has been produced.

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 , because it has three valence electrons

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 for 1.0 g of each of the two substances? (The specific heat of water is 4.2 J/(g•°C).)

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

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.

The reaction between NO(g) and 02(g) to produce N02(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 provides the correct explanation?

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

The mass spectrum of an average sample of a pure element is shown in the figure above. Which of the following is the identity of the element?

Zr

When a strong acid is titrated with a strong base using phenolphthalein as an indicator, the color changes abruptly at the endpoint of the titration and can be switched back and forth by the addition of only one drop of acid or base. The reason for the abruptness of this color change is that

a large change in pH occurs near the endpoint of the titration