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POST UTME UNIBEN 2020 Chemistry | Objective

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Question 1

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. \( k = 0.05 , \text{M}^{-1} , \text{s}^{-1} \)

B. \( k = 0.1 , \text{M}^{-1} , \text{s}^{-1} \)

C. \( k = 0.2 , \text{M}^{-1} , \text{s}^{-1} \)

D. \( k = 0.05 , \text{M}^{-1} , \text{min}^{-1} \)

Correct Answer: A

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Question 2

A 2.5 g sample of a polymer is dissolved in 50 mL of a solvent. The osmotic pressure of the solution is 2.5 atm at 25°C. Calculate the molar mass of the polymer.

A. \( 500 , \text{g/mol} \)

Correct B. \( 1000 , \text{g/mol} \)

C. \( 2000 , \text{g/mol} \)

D. \( 5000 , \text{g/mol} \)

Correct Answer: B

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Question 3

A 10 mL sample of a solution containing 0.1 M NaOH is titrated with 0.1 M HCl. Calculate the volume of HCl required to reach the equivalence point.

A. \( 10 , \text{mL} \)

Correct B. \( 20 , \text{mL} \)

C. \( 30 , \text{mL} \)

D. \( 40 , \text{mL} \)

Correct Answer: B

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Question 4

A 2.0 g sample of a metal is heated in a crucible until it melts. The mass of the crucible and the metal is 2.5 g. The mass of the crucible alone is 1.5 g. Calculate the molar mass of the metal.

A. \( 50 , \text{g/mol} \)

B. \( 100 , \text{g/mol} \)

Correct C. \( 200 , \text{g/mol} \)

D. \( 500 , \text{g/mol} \)

Correct Answer: C

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Question 5

A 5.0 g sample of a gas is collected over water at a temperature of 25°C and a pressure of 1 atm. The volume of the gas is 10 L. Calculate the molar mass of the gas.

A. \( 20 , \text{g/mol} \)

B. \( 40 , \text{g/mol} \)

Correct C. \( 60 , \text{g/mol} \)

D. \( 80 , \text{g/mol} \)

Correct Answer: C

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Question 6

Calculate the s\tandard enthalpy change for the reaction: 2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s). The s\tandard enthalpy of formation for Al2O3(s) is -1675.7 kJ/mol, and the s\tandard enthalpy of formation for Fe2O3(s) is -824.2 kJ/mol. The s\tandard enthalpy of formation for Al(s) is 0 kJ/mol, and the s\tandard enthalpy of formation for Fe(s) is 0 kJ/mol.

Correct A. -1811.9 kJ/mol

B. -1811.5 kJ/mol

C. -1812.1 kJ/mol

D. -1812.3 kJ/mol

Correct Answer: A

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Question 7

A 2.50 M solution of NaOH is electrolyzed u\sing a platinum electrode. The electrolysis is carried out at 25°C. Calculate the mass of oxygen gas produced at the anode after 2.00 hours.

A. 0.125 g

Correct B. 0.250 g

C. 0.375 g

D. 0.500 g

Correct Answer: B

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Question 8

The atomic radius of an element is 100 pm. If the element has an electron configuration of [Ar] 4s^2 3d^5, what is the expected oxidation state of the element?

A. +2

B. +3

C. +4

Correct D. +5

Correct Answer: D

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Question 9

A polymer has a molecular weight of 100,000 g/mol. If the polymer has a degree of polymerization of 500, what is the molecular weight of the repeating unit?

A. 200 g/mol

B. 250 g/mol

C. 300 g/mol

Correct D. 400 g/mol

Correct Answer: D

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Question 10

A solution of 0.10 M NaOH is titrated with a solution of 0.10 M HCl. If 25.0 mL of HCl is required to reach the equivalence point, what is the volume of NaOH required to reach the equivalence point?

Correct A. 25.0 mL

B. 50.0 mL

C. 75.0 mL

D. 100 mL

Correct Answer: A

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Question 11

A solution of 0.1 M NaOH is titrated with 0.1 M HCl. At the equivalence point, the pH of the solution is 7. Calculate the volume of HCl required to reach the equivalence point.

A. 10 mL

Correct B. 20 mL

C. 30 mL

D. 40 mL

Correct Answer: B

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Question 12

The reaction between HCl and NaOH is represented by the equation: HCl + NaOH → NaCl + H2O. If 25 mL of 0.1 M HCl is added to 25 mL of 0.1 M NaOH, what is the concentration of the resulting solution?

A. 0.05 M

Correct B. 0.1 M

C. 0.15 M

D. 0.2 M

Correct Answer: B

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Question 13

A 0.1 M solution of HCl is titrated with a 0.1 M solution of NaOH. At the equivalence point, the pH of the solution is 7. What is the volume of NaOH required to reach the equivalence point?

A. 10 mL

Correct B. 20 mL

C. 30 mL

D. 40 mL

Correct Answer: B

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Question 14

A. 0.05 M

Correct B. 0.1 M

C. 0.15 M

D. 0.2 M

Correct Answer: B

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Question 15

A 0.1 M solution of HCl is titrated with a 0.1 M solution of NaOH. At the equivalence point, the pH of the solution is 7. What is the volume of NaOH required to reach the equivalence point?

A. 10 mL

Correct B. 20 mL

C. 30 mL

D. 40 mL

Correct Answer: B

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