Chemistry Department Chem-202, Final Exam Time

B

1

B

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King Abdulaziz University

Faculty of Science - Chemistry Department Chem-202, Final Exam

Time: 120 minutes

Name: Number: Section:

Useful information:

Gas constant (R) = 8.314 J/K.mol OR 0.082 L.atm/K.mol Proton mass = 1.007825 amu

Neutron mass = 1.008665 amu 1amu = 1.49 x10^-10 J

Choose the correct answer:

B-1

Under standard-state conditions, which of the following half-reactions occurs at the cathode during the electrolysis of aqueous nickel sulfate at 25C?

a. 2H

2

O + 2e

^

 H

2

+ 2OH

^

b. Ni

²⁺

+ 2e

^

 Ni

c. 2H

2

O  O

2

+ 4H

⁺

+ 4e

^

d. Ni  Ni

²⁺

+ 2e

^

B-2

A current of 2.50 A was passed through an electrolytic cell containing molten CaCl2 for 4.50 hours. How many moles of calcium metal should be deposited?

a. 5.83  10

^5

mol b. 0.420 mol c. 0.210 mol d. 0.840 mol

B-3

How many coulombs of charge are required to cause reduction of 0.20 mole of Cr³⁺ to Cr?

a. 3.0 C b. 9.65 C c. 2.9  10

⁴

C d. 5.8  10

⁴

C

B-4

The half-reaction occurring at the cathode during electrolysis of an aqueous copper(II) iodide solution is

a. 2I

^

 I

2

+ 2e

^

b. Cu  Cu

²⁺

+ 2e

^

c. Cu

²⁺

+ 2e

^

 Cu

d. I

2

+ 2e

^

 2I

^

B

3

B-5

Calculate the cell emf for the following reaction at 25C:

Ni(s) + 2Cu²⁺(0.010 M)  Ni²⁺(0.0010 M) + 2Cu⁺(1.0 M); [E^o Cu⁺²/Cu¹⁺ = 0.153 V; E^o Ni⁺²/Ni = -0.257 V]

a. -0.43 V b. 0.34 V c. 0.43 V d. 0.40 V

B-6

Determine the equilibrium constant (K_eq) at 25C for the reaction E0cel=0. 29V Cl2(g) + 2Br^ (aq) 2Cl^ (aq) + Br2(l)

a. 1.5  10

^10

b. 6.3  10

⁹

c. 1.3  10

⁴¹

d. 8.1  10

⁴

B-7

According to the following cell diagram, which chemical species undergoes reduction?

Sn | Sn²⁺ || NO3

(acid soln), NO(g) | Pt

a. Sn

²⁺

b. NO c. NO

3



d. Pt

B-8

The overall reaction 2Co³⁺(aq) + 2Cl^(aq)  2Co²⁺(aq) + Cl2(g) has the standard cell voltage Ecell= 0.46 V. Given that Cl₂(g) + 2e^  2Cl^ (aq), E = 1.36 V,

calculate the standard reduction potential for the following the half reaction at 25C:

Co³⁺ + e^  Co²⁺

a. 1.82 V

b. 0.90 V c. -0.90 V d. -1.36 V

B-9

For the reaction, 2Cr²⁺ + Cl₂(g)  2Cr³⁺ + 2Cl^, Ecell is 1.78 V. Calculate Ecell for the related reaction Cr³⁺ + Cl^  Cr²⁺ + (1/2)Cl₂(g).

a. 0.89 V b. - 0.89 V c.- 1.78 V d. 1.78V

B-10

Calculate E_cell for a silver-aluminum cell in which the cell reaction is Al(s) + 3Ag⁺(aq)  Al³⁺(aq) + 3Ag(s)

a. 0.86 V b. 2.46 V c. - 0.86 V d. 0.0V

B-11

Which type of nuclear process requires an extremely high temperature (millions of degrees)?

a. alpha decay b. fission reaction c. fusion reaction d. beta decay

B-12

What is the nuclear binding energy per nucleon, in joules, for 25

12 Mg (atomic mass 24.985839 amu). Data: 1 kg = 6.022  10²⁶ amu; c = 3.00  10⁸ m/s.

B

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a. 0.999 J/nucleon b. 3.30 x10

^11

J/nucleon c. 1.3x10

^12

J/nucleon d. 0.22076 J/nucleon

B-13

Polonium-208 is an alpha emitter with a half-life of 2.90 years. How many milligrams of polonium from an original sample of 2.00 mg will remain after 8.00

years?

a. 0.296 mg b. 6.77 mg c. 0.147 mg d. 0.725 mg B-14

Sulfur-35 decays by beta emission. The decay product is

a. 35

17 Cl b. 31

30 Si c. 34

17 Cl d. 34

16 S

B-15

Which of the following statements is false

a. A catalyst may be altered in the reaction, but is always regenerated.

b. A catalyst alters the mechanism of reaction.

c. A catalyst alters the activation energy.

d. A catalyst increases the rate of the forward reaction, but does

not alter the reverse rate at equilibrium.

B-16

The rate law for the reaction H₂O₂ + 2H⁺ + 2I ^  I₂ + 2H₂O is rate = k[H2O2][I ^-]. The following mechanism has been suggested.

H2O2 + I ^  HOI + OH ^ slow OH ^ + H⁺  H2O fast HOI + H⁺ + I ^  I2 + H2O fast

Identify all intermediates included in this mechanism.

a. H

⁺

only b. H

⁺

and HOI c. HOI and OH

^-

d. H

⁺

and I

-

B-17

Calculate the activation energy, in kJ/mol, for the redox reaction

Sn²⁺ + 2Co³⁺  Sn⁴⁺ + 2Co²⁺.

Data: Temp (C) k (1/M·s) 3.12  10³ 2 27.0  10³ 27

a. 59.2 b. 163 kJ c. 5.37 d. 48.1 kJ

B

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B-18

The reaction 2NO₂(g)  2NO(g) + O2(g) is suspected to be second order in NO2. Which of the following kinetic plots would be the most useful to confirm

whether or not the reaction is second or

a. a plot of ln [NO

2

]

^1

vs. t b. a plot of ln [NO

₂

] vs. t c. a plot of [NO

2

] vs. t d. a plot of [NO

₂

]

^1

vs. t

B-19

The isomerization of cyclopropane to form propene H2C — CH2

\ /  CH₃ CH = CH₂ CH2

is a first-order reaction. At 760 K, 15% of a sample of cyclopropane changes to propene in 6.8 min. What is the half-life of cyclopropane at 760 K?

a. 29 min b. 2.5 min c. 23 min d. 3.4  10

^2

min B-20

Appropriate units for a second-order rate constant are

a. M/s

b. 1/s c. 1/M·s d. 1/M

²

·s

B-21

A first-order reaction has a rate constant of 3.00  10^3 s^1. The time required for the reaction to be 80.0% complete is

a. 462 s b. 536 s c. 231 s d. 41.7 s

B-22

For the hypothetical reaction A + 3B  2C, the rate should be expressed as

a. rate = 1/2 ([C]/t) b. rate = - [C]/t c. rate = -3 ([B]/t)

d. rate =

[A]/t

B-23

For the overall chemical reaction shown below, which one of the following statements can be rightly assumed?

2H2S(g) + O2(g)  2S(s) + 2H2O(l)

a. The rate law cannot be determined from the information given b. The reaction is second-order overall.

c. The rate law is, rate = k[H

2

S] [O

2

].

B

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d. The reaction is third-order overall.

B-24

For the following reaction, P(C6H14)/t was found to be 6.2  10^3 atm/s.

C6H14(g)  C6H6(g) + 4H2(g); Determine P(H2)/t for this reaction at the same time.

a. 6.2  10

^3

atm/s b. 1.6  10

^3

atm/s c. 2.5  10

^2

atm/s d. -1.6  10

^3

atm/s

B-25

What is the osmotic pressure of a solution that contains 13.7 g of propyl alcohol (C3H7OH) dissolved in enough water to make 500. mL of solution at

27^oC?

a. 11.2 atm b. 0.456 atm c. 0.01 atm d. 0.037 atm

B-26

Calculate the freezing point of a solution made from 22.0 g of octane (C8H18) dissolved in 148.0 g of benzene. Benzene freezes at 5.50C and its K_f value is

5.12C/m.

a. -1.16C b. 12.2C c. 6.66C d. 5.49C

B-27

The solubility of CO₂ gas in water

a. increases with increasing temperature.

b. decreases with decreasing temperature.

c. is not dependent on temperature.

d. decreases with increasing temperature.

B-28 Consider a solution made from a nonvolatile solute and a volatile solvent. Which statement is true?

a. The vapor pressure of the solution is always greater than the vapor pressure of the pure solvent.

b. The boiling point of the solution is always greater than the boiling point of the pure solvent.

c. The freezing point of the solution is always greater than the freezing point of the pure solvent.

d. All the same

B-29

Which of the following compounds should be soluble in CCl4?

B

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a. NaCl

b. NaOH c. H

2

O d. C

8

H

18

B-30

Calculate the percent by mass of potassium nitrate in a solution made from 45.0 g KNO₃ and 295 mL of water. The density of water is 0.997 g/mL

a.1.51% b. 13.3 % c. 15.2 % d.7.57 %

B-31

For the reaction H₂(g) + S(s)  H2S(g), H = 20.2 kJ/mol and S = +43.1 J/K·mol. Which of the following statements is true?

a.The reaction is only spontaneous at low temperatures.

b. The reaction is spontaneous only at high temperatures.

c. G becomes less favorable as temperature increases.

d.The reaction is spontaneous at all temperatures.

B-32

Determine S for the reaction: SO3(g) + H₂O(l)  H2SO₄(l).

S(J/K·mol)

SO3 256.2

H₂O 69.9 H₂SO₄ 156.9

a. 169.2 J/K·mol b. 1343.2 J/K·mol

c. 29.4 J/K·mol d. -169.2 J/K·mol

B-33

The entropy change on vaporization (S_vap) of a compound or element is:

a. always negative. b. always zero.

c. sometimes is positive and sometimes is negative. d. always positive.

B-34

Ozone (O3) in the atmosphere can reaction with nitric oxide (NO):

O₃(g) + NO(g)  NO2(g) + O₂(g).

Calculate the G for this reaction at 25C. (H = 199 kJ/mol, S = 4.1 J/K·mol)

a. 198 kJ/mol b. - 1.22 x 103kJ/mol c. -198kJ/mol d. 2.00x103 kJ/mol

B-35

How much heat is required to raise the temperature of 1,500 g of water from 25°C to 52°C? The specific heat of water is 4.184 J/g·°C

a. 1,500 kJ b. 169 kJ c. 6.27 kJ d. 40.5 J

B

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B-36

A 0.1326 g sample of magnesium was burned in an oxygen bomb calorimeter. The total heat capacity of the calorimeter plus water was 5,760 J/°C. If the temperature rise of the calorimeter with water was 0.570°C, calculate the enthalpy of combustion of magnesium.

Mg(s) + 1/2O2(g)  MgO(s)

a. 6020 kJ/mol b. 24.8 kJ/mol c. 435 kJ/mol d. 602 kJ/mol

B-37

Find the standard enthalpy of formation of ethylene, C2H4(g), given the following data: heat of combustion of C2H4(g)= 1411 kJ/mol; Hf[CO2(g)] = 393.5 kJ/mol;

Hf [H2O(l)] = 285.8 kJ/mol.

a. 52 kJ/mol b. 87 kJ/mol c. 731 kJ/mol d. 1.41  10

³

kJ/mol

B-38 Which of the following process is endothermic a. H

2

O(s)  H

2

O(l)

b. H

2

O(g)  H

2

O(l)

c. 3O

₂

(g) + 2CH

₃

OH(g)  2CO

2

(g) + 2H

₂

O(g) d. O

2

(g) + 2H

2

(g)  2H

2

O(g)

B-39

Sodium carbonate can be made by heating sodium bicarbonate:

2NaHCO3(s)  Na2CO3(s) + CO2(g) + H2O(g)

Given that H = 128.9 kJ/mol and G = 33.1 kJ/mol at 25C, above what minimum temperature will the reaction become spontaneous under standard state conditions?

a. 3.9 K b. 401K c. 0.321 K d. 525 K

B-40

The equilibrium constant at 427C for the reaction N2(g) + 3H2(g) 2NH3(g) is Kp = 9.4  10^5. Calculate the value of G for the reaction under these conditions:

a. -33 kJ/mol b. 54 kJ/mol c. -54 kJ/mol d. 33kJ/mol