The density of the solution is 1.00 g/mL

1092-1st Midterm Exam_04/14/21_(A)

MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

1) The vapor pressure of pure ethanol at 333 K is 0.459 atm. Raoult's Law predicts that a solution prepared by dissolving 10.0 mmol naphthalene (nonvolatile) in 90.0 mmol ethanol will have a vapor pressure of __________ atm.

A) 0.367 B) 0.413 C) 0.0918 D) 0.498 E) 0.790

Answer: B

2)At 293 k, a 4.79 M aqueous solution of ammonium chloride has a density of 1.0674 g/mL. What is the molality of ammonium chloride in the solution? The formula weight of NH4Cl is 53.50 g/mol.

A) 0.0955 B) 4.79 C) 24.00 D) 0.223 E) 5.90

Answer: E

3)The osmotic pressure of a solution formed by dissolving 85.0 mg of aspirin (C9H8O4) in 0.250 L of water at 25 °C is __________ atm. ( R = 0.0821 L-atm / mol-K )

A) 0.0462 B) 4.68 C) 3.88 × 10-3 D) 46.2 E) 8.32

Answer: A

4) The ratio of the actual value of a colligative property to the value calculated, assuming the substance to be a nonelectrolyte, is referred to as __________.

A) vapor pressure lowering B) freezing point depression C) osmotic pressure

D) Henry's law

E) the van't Hoff factor Answer: E

5)Which one of the following substances is more likely to dissolve in CCl4?

A) HCl B) NaCl C) HBr

D)CH3CH2OH E)CBr4

Answer: E

6) A solution contains 15 ppm of benzene. The density of the solution is 1.00 g/mL. This means that __________.

A) 100 g of the solution contains 15 mg of benzene B) the solution is 15% by mass of benzene

C) the molarity of the solution is 15

D) there are 15 mg of benzene in 1.0 L of this solution E) 100 g of the solution contains 15 g of benzene Answer: D

7) The concentration of sodium chloride in an aqueous solution that is 2.02 M and that has a density of 1.01 g/mL is __________% by mass.

A) 7.83 B) 2.01 C) 118 D) 11.7 E) 18.1

Answer: D

8)A solution containing 15.0 g of an unknown liquid and 90.0 g water has a freezing point of -3.33 °C. Given Kf = 1.86°C/m for water, the molar mass of the unknown liquid is __________ g/mol.

A) 333 B) 69.0 C) 93.0 D) 161 E) 619

Answer: C

9)The concentration of HCl in a solution that is prepared by dissolving 11 g of HCl in 200 g of C2H6O is __________ molal.

A) 27.5 B) 3.3 × 10-2 C) 7.5 × 10-4 D) 1.3 E) 1.5

Answer: E

10)A solution is prepared by dissolving 6.50 g of glycerin (C3H8O3) in 201 g of ethanol (C2H5OH). The freezing point of the solution is __________°C. The freezing point of pure ethanol is -114.6 °C at 1 atm. The molal-freezing-point-depression constant (Kf) for ethanol is 1.99 °C/m. The molar masses of glycerin and of ethanol are 92.1 g/mol and 46.1 g/mol, respectively.

A) 0.699 B) -120.8 C) -108.4 D) -113.9 E) -115.3

Answer: E

11)A solution is prepared by dissolving 13.0 g of NH3 in 250.0 g of water. The density of the resulting solution is 0.974 g/mL. The mole fraction of NH3 in the solution is __________.

A) 16.8 B) 0.0522 C) 0.940 D) 0.922 E) 0.0520

Answer: B

12) Pressure has an appreciable effect on the solubility of __________ in liquids.

A) solids and liquids B) gases

C) salts D) liquids

E) solids Answer: B

13)Calculate the freezing point of a 0.05500 m aqueous solution of NaNO3. The molal freezing-point-depression constant of water is 1.86 °C/m.

A) -0.0562 B) -0.106 C) 0.0286 D) 0.106 E) -0.205

Answer: E

14) Of the concentration units below, only __________ is temperature dependent.

A) molality B) mass % C) molarity D) ppm E) ppb

Answer: C

15) The rate constant for a reaction is 0.13 M-1s-1. If the initial concentration of reactant is 0.26 mol/L, it takes __________ s for the concentration to decrease to 0.11 mol/L.

A) 0.017 B) 9.1 C) 5.2 D) 0.68 E) 40.

Answer: E

16) A reaction was found to be zero order in A. Increasing the concentration of A by a factor of 3 will cause the reaction rate to __________.

A) increase by a factor of 9 B) remain constant C) triple

D) decrease by a factor of the cube root of 3 E) increase by a factor of 27

Answer: B

The peroxydisulfate ion (S2O82-) reacts with the iodide ion in aqueous solution via the reaction:

S2O82- (aq) + 3I- 2SO4 (aq) + I3- (aq)

An aqueous solution containing 0.050 M of S2O82- ion and 0.072 M of I- is prepared, and the progress of the reaction followed by measuring [I-]. The data obtained is given in the table below.

Time (s) 0.000 400.0 800.0 1200.0 1600.0 [I-] (M) 0.072 0.057 0.046 0.037 0.029 17) The concentration of S2O82- remaining at 1600 s is __________ M.

A) 0.029 B) 0.064 C) 0.014 D) 0.043 E) 0.036

Answer: E

18) At elevated temperatures, methylisonitrile (CH3NC) isomerizes to acetonitrile (CH3CN):

CH3NC (g) CH3CN (g)

The dependence of the rate constant on temperature is studied and the graph below is prepared from the results.

The energy of activation of this reaction is __________ kJ/mol.

A) 4.4 × 10-7 B) 4.4 × 10-4 C) 1.9 × 104 D) 160 E) 1.6 × 105

Answer: D

A flask is charged with 0.124 mol of A and allowed to react to form B according to the reaction A(g) B(g). The following data are obtained for [A] as the reaction proceeds:

Time (s) 0.00 10.0 20.0 30.0 40.0 Moles of A 0.124 0.110 0.088 0.073 0.054

19) The average rate of disappearance of A between 20 s and 40 s is __________ mol/s.

A) 1.4 × 10-3 B) 1.7 × 10-3 C) 8.5 × 10-4 D) 7.1 × 10-3 E) 590 Answer: B

20) If the rate law for the reaction 2A + 3B products

is first order in A and second order in B, then the rate law is rate = __________.

A) k[A][B] B) k[A]2[B]3 C) k[A]2[B]2 D) k[A][B]2 E) k[A]2[B]

Answer: D

21) Which one of the following graphs shows the correct relationship between concentration and time for a reaction that is second order in [A]?

A)

B)

C)

D)

E)

Answer: A 22)The reaction

2NO2 2NO + O2

follows second-order kinetics. At 300 °C, [NO2] drops from 0.0100 M to 0.00650 M in 100.0 s. The rate constant for the reaction is __________M-1s-1.

A) 0.096 B) 0.54 C) 0.65 D) 0.81 E) 1.2

Answer: B

23) At elevated temperatures, dinitrogen pentoxide decomposes to nitrogen dioxide and oxygen:

2N2O5(g) 4NO2 (g) + O2 (g)

When the rate of formation of NO2 is 5.5 × 10-4 M/s, the rate of decomposition of N2O5 is ________ M/s.

A) 10.1 × 10-4 B) 5.5 × 10-4 C) 2.8 × 10-4 D) 1.4 × 10-4 E) 2.2 × 10-3 Answer: C

24) A particular first-order reaction has a rate constant of 1.35 × 102 s-1 at 25.0 °C. What is the magnitude of k at 75.0°C if Ea = 75.5 kJ/mol?

A) 3.40 × 106 B) 1.36 × 102 C) 1.08 × 104 D) 3.06 × 104 E) 591 Answer: C

25) The isomerization of methylisonitrile to acetonitrile CH3NC (g) CH3CN (g)

is first order in CH3NC. The rate constant for the reaction is 3.22 × 10-4 s-1 at 493 K. The half-life of the reaction when the initial [CH3NC] is 0.030 M is __________ s.

A) 1.04 × 105 B) 2.15 × 103 C) 1.55 × 103 D) 4.64 × 10-4 E) 3.11 × 103 Answer: B

The data in the table below were obtained for the reaction:

A + B P Experiment

Number [A] (M) [B] (M) Initial Rate (M/s)

1 0.273 0.763 2.83

2 0.273 1.526 2.83

3 0.819 0.763 25.47

26) The magnitude of the rate constant is __________.

A) 42.0 B) 13.2 C) 0.278 D) 38.0 E) 2.21

Answer: D

27) Nitrogen dioxide decomposes to nitric oxide and oxygen via the reaction:

2NO2 2NO + O2

In a particular experiment at 300 °C, [NO2] drops from 0.0100 to 0.00750 M in 100 s. The rate of appearance of O2 for this period is __________ M/s.

A) 2.5 × 10-5 B) 5.0 × 10-3 C) 2.5 × 10-3 D) 1.3 × 10-5 E) 5.0 × 10-5 Answer: D

28) The combustion of ethylene proceeds by the reaction C2H4 (g) + 3O2 (g) 2CO2 (g) + 2H2O (g)

When the rate of disappearance of O2 is 0.33 M s-1, the rate of appearance of CO2 is __________ M s-1.

A) 0.50 B) 0.99 C) 0.66 D) 0.11 E) 0.22

Answer: E

29) Given the following reaction at equilibrium at 300.0 K:

NH4HS (s) NH3 (g) + H2S (g) If pNH3 = pH2S = 0.111 atm, Kp = __________.

A) 5.66 x 10-3 B) .0123 C) 4.99 x 10-4 D) .0821 E) .111

Answer: B

30) Given the following reaction at equilibrium, if Kc = 5.84 x 105 at 230.0 °C, Kp = __________.

2NO (g) + O2 (g) 2NO2 (g)

A) 2.40 x 106 B) 1.41 x 104 C) 2.41 x 107 D) 3.67 x 10-2 E) 6.44 x 105 Answer: B

31) The value of Keq for the equilibrium N2 (g) + O2 (g) 2 NO (g)

is 4.2 x 10-31 at 27 °C. What is the value of Keq for the equilibrium below?

4 NO (g) 2 N2 (g) + 2 O2 (g)

A) 8.4 x 10-31 B) 4.2 x 1031 C) 8.4 × 1031 D) 5.7 x 1060

E) none of the above Answer: D

32) Which of the following expressions is the correct equilibrium-constant expression for the following reaction ?

CO2 (g) + 2H2 (g) CH3OH (g) A) [CH3OH]

[CO2][H2]

B) [CO2][H2]2 [CH3OH]

C) [CH3OH]

[CO2]

D) [CH3OH]

[CO2][H2]2 E) [CO2][H2]

[CH3OH]

Answer: D

33) Given the following reaction at equilibrium at 450.0 °C:

CaCO3 (s) CaO (s) + CO2 (g) If pCO2 = 0.0170 atm, Kc = __________.

A) 0.0821 B) 10.1 C) 1.01 D) 170 E) 2.86 x 10-4

Answer: E

34) Consider the following reaction at equilibrium:

2CO2 (g) 2CO (g) + O2 (g) H° = -514 kJ

Le Châtelier's principle predicts that an increase in temperature will __________.

A)increase the partial pressure of O2 (g) B)decrease the partial pressure of CO2 (g) C) increase the partial pressure of CO

D) increase the value of the equilibrium constant E) decrease the value of the equilibrium constant Answer: E

35) Dinitrogentetraoxide partially decomposes according to the following equilibrium:

N2O4 (g) 2NO2 (g)

A 1.00-L flask is charged with 0.0400 mol of N2O4. At equilibrium at 100 °C, 0.0055 mol of N2O4 remains.

Keq for this reaction is __________.

A) 2.2 × 10-4 B) 0.87 C) 13 D) 0.22 E) 0.022

Answer: B

36) In the coal-gasification process, carbon monoxide is converted to carbon dioxide via the following reaction:

CO (g) + H2O (g) CO2 (g) + H2 (g)

In an experiment, 0.35 mol of CO and 0.40 mol of H2O were placed in a 1.00-L reaction vessel.

At equilibrium, there were 0.17 mol of CO remaining. Keq at the temperature of the experiment is _________.

A) 0.75 B) 5.5 C) 1.2 D) 1.0 E) 0.87

Answer: E

37) Consider the following chemical reaction:

H2 (g) + I2 (g) 2HI (g)

At equilibrium in a particular experiment, the concentrations of H2, I2, and HI were 0.15 M, 0.033 M, and 0.55 M, respectively. The value of Keq for this reaction is __________.

A) 0.0090 B) 23 C) 61 D) 111 E) 5.1

Answer: C

38) The expression for Kp for the reaction below is __________.

4CuO (s) + CH4 (g) CO2 (g) + 4Cu (s) + 2H2O (g) A) [Cu] PCO₂PH₂O 2

[CuO]4 PCH₄ B) PCO₂PH₂O 2

PCH₄

C) PCH₄

PH₂O 2 PCO₂ D) PCH₄

PCO₂PH₂2 E) PCO₂PH₂O 2

PCuO Answer: B

39) The equilibrium expression for Kp for the reaction below is __________.

2O3 (g) 3O2 (g) A)

2P

3P

3P

2P

P

P

3P

2P

P

P

Answer: E

40) The equilibrium expression for Kp for the reaction below is __________.

N2 (g) + O2 (g) 2NO (g) A)

(P

(P

P

(2P

(2P

)(2P

C)

(P

(P

2P

(2P

(2P

2P