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POST UTME AL-HIKMAH UNIVERSITY 2021 Chemistry | Objective

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Question 1

Determine the s\tandard Gibbs free energy change for the reaction: 2Ag+(aq) + 2Cl-(aq) → 2AgCl(s) at 298 K.

A. -120 kJ/mol

Correct B. -240 kJ/mol

C. -300 kJ/mol

D. -400 kJ/mol

Correct Answer: B

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Question 2

A 2.5 L flask contains 0.25 mol of an ideal gas at 298 K. Calculate the pressure of the gas u\sing the ideal gas law.

Correct A. 1.01 × 10^5 Pa

B. 2.02 × 10^5 Pa

C. 3.03 × 10^5 Pa

D. 4.04 × 10^5 Pa

Correct Answer: A

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Question 3

The half-life of a radioactive subs\tance is 5.0 years. If 100 g of the subs\tance initially decays to 50 g, how many years will it take for the subs\tance to decay to 25 g?

A. 10 years

Correct B. 15 years

C. 20 years

D. 25 years

Correct Answer: B

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Question 4

A 0.5 M solution of HCl is mixed with a 0.5 M solution of NaOH. What is the pH of the resulting solution?

A. 1

Correct B. 2

C. 3

D. 4

Correct Answer: B

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Question 5

A 2.0 L flask contains 0.5 mol of an ideal gas at 300 K. Calculate the work done by the gas when it expands from 2.0 L to 4.0 L against a cons\tant external pressure of 1.0 atm.

A. 2.0 J

B. 4.0 J

Correct C. 6.0 J

D. 8.0 J

Correct Answer: C

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Question 6

Determine the rate cons\tant (k) for the reaction: 2NO(g) + O2(g) → 2NO2(g), given that the initial concentrations of NO and O2 are 0.1 M and 0.2 M, respectively, and the rate of disappearance of NO is 0.05 M/s after 10 minutes.

Correct A. 0.05 min^-1

B. 0.1 min^-1

C. 0.2 min^-1

D. 0.3 min^-1

Correct Answer: A

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Question 7

A 0.1 M solution of AgNO3 is mixed with a 0.1 M solution of NaCl. What is the concentration of AgCl(s) that will precipitate out of the solution?

Correct A. 0.05 M

B. 0.1 M

C. 0.15 M

D. 0.2 M

Correct Answer: A

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Question 8

A 2.0 L flask contains 0.5 mol of CO2 at 298 K. What is the partial pressure of CO2 in the flask?

A. 0.1 atm

Correct B. 0.2 atm

C. 0.3 atm

D. 0.4 atm

Correct Answer: B

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Question 9

A 1.0 M solution of HCl is mixed with a 1.0 M solution of NaOH. What is the pH of the resulting solution?

A. 1

Correct B. 2

C. 3

D. 4

Correct Answer: B

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Question 10

A 0.1 M solution of CaCl2 is mixed with a 0.1 M solution of Na2SO4. What is the concentration of CaSO4(s) that will precipitate out of the solution?

Correct A. 0.05 M

B. 0.1 M

C. 0.15 M

D. 0.2 M

Correct Answer: A

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Question 11

Determine the number of moles of $\text{CO}_2$ produced when 2.5 moles of $\text{CaC}_2$ react with excess $\text{H}_2\text{O}$ according to the equation $\text{CaC}_2 + 2\text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{C} + \text{CO}_2$.

Correct A. 1.25

B. 2.5

C. 5

D. 10

Correct Answer: A

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Question 12

A solution contains 2.5 g of $\text{NaCl}$ per 100 mL of solution. What is the molarity of the solution?

A. 0.1 M

Correct B. 0.2 M

C. 0.5 M

D. 1 M

Correct Answer: B

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Question 13

A 2.5 L flask contains 0.5 mol of $\text{O}_2$ at 25°C. What is the partial pressure of $\text{O}_2$ in the flask?

Correct A. 0.5 atm

B. 1 atm

C. 2 atm

D. 5 atm

Correct Answer: A

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Question 14

A 2.5 L flask contains 0.5 mol of $\text{O}_2$ at 25°C. What is the partial pressure of $\text{O}_2$ in the flask?

Correct A. 0.5 atm

B. 1 atm

C. 2 atm

D. 5 atm

Correct Answer: A

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Question 15

A 2.5 L flask contains 0.5 mol of $\text{O}_2$ at 25°C. What is the partial pressure of $\text{O}_2$ in the flask?

Correct A. 0.5 atm

B. 1 atm

C. 2 atm

D. 5 atm

Correct Answer: A

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Question 16

The s\tandard electrode potential for the reaction Zn2+ + 2e- → Zn is -0.76 V. What is the s\tandard electrode potential for the reaction Zn → Zn2+ + 2e-?

A. -0.76 V

B. 0.76 V

C. 1.52 V

Correct D. -1.52 V

Correct Answer: D

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Question 17

The half-reaction Zn → Zn2+ + 2e- has a s\tandard electrode potential of -0.76 V. What is the s\tandard electrode potential for the reaction Zn2+ + 2e- → Zn?

A. 0.76 V

Correct B. -0.76 V

C. 1.52 V

D. -1.52 V

Correct Answer: B

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Question 18

The s\tandard electrode potential for the reaction Zn2+ + 2e- → Zn is -0.76 V. What is the s\tandard electrode potential for the reaction Zn → Zn2+ + 2e-?

A. 0.76 V

Correct B. -0.76 V

C. 1.52 V

D. -1.52 V

Correct Answer: B

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Question 19

The s\tandard electrode potential for the reaction Zn2+ + 2e- → Zn is -0.76 V. What is the s\tandard electrode potential for the reaction Zn → Zn2+ + 2e-?

A. 0.76 V

Correct B. -0.76 V

C. 1.52 V

D. -1.52 V

Correct Answer: B

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Question 20

The half-reaction Zn → Zn2+ + 2e- has a s\tandard electrode potential of -0.76 V. What is the s\tandard electrode potential for the reaction Zn2+ + 2e- → Zn?

A. 0.76 V

Correct B. -0.76 V

C. 1.52 V

D. -1.52 V

Correct Answer: B

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Question 21

Determine the number of moles of acetic acid (CH3COOH) that can be obtained from 250 mL of a 0.5 M solution of sodium acetate (CH3COONa) when it is mixed with 100 mL of 1 M hydrochloric acid (HCl).

A. 0.125 mol

Correct B. 0.25 mol

C. 0.5 mol

D. 1 mol

Correct Answer: B

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Question 22

A 25 mL sample of a 0.1 M solution of sodium hydroxide (NaOH) is titrated with a 0.5 M solution of hydrochloric acid (HCl). Calculate the pH of the resulting solution after the addition of 10 mL of the acid.

A. 1

B. 2

C. 3

Correct D. 4

Correct Answer: D

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Question 23

The half-life of a radioactive subs\tance is 10 years. If the initial amount of the subs\tance is 100 g, what is the amount remaining after 30 years?

Correct A. 12.5 g

B. 25 g

C. 50 g

D. 100 g

Correct Answer: A

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Question 24

A 2.0 g sample of a polymer is dissolved in 100 mL of a solvent. If the density of the solution is 1.2 g/mL, what is the molar mass of the polymer?

A. 100 g/mol

B. 200 g/mol

Correct C. 500 g/mol

D. 1000 g/mol

Correct Answer: C

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Question 25

A 50 mL sample of a 0.2 M solution of sodium carbonate (Na2CO3) is titrated with a 0.5 M solution of hydrochloric acid (HCl). Calculate the pH of the resulting solution after the addition of 20 mL of the acid.

A. 1

B. 2

C. 3

Correct D. 4

Correct Answer: D

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