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POST UTME UNN 2021 Chemistry | Objective

Are you preparing for POST UTME UNN exams? Reviewing past questions is one of the most effective ways to guarantee a high score. This practice hub features authentic 2021 Chemistry (Objective) questions designed to simulate the real exam environment.

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Question 1

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

Correct A. -1651.4 kJ/mol

B. -1675.7 kJ/mol

C. -1699.0 kJ/mol

D. -1712.3 kJ/mol

Correct Answer: A

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Question 2

The reaction of 2.5 g of an unknown hydrocarbon with 100 cm³ of 0.5 M HCl produces 1.25 g of CO2. Calculate the empirical formula of the hydrocarbon.

Correct A. C2H4

B. C3H6

C. C4H8

D. C5H10

Correct Answer: A

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Question 3

A 0.5 M solution of H2SO4 is titrated with 0.5 M NaOH. The initial volume of the acid is 25 cm³. After the addition of 20 cm³ of NaOH, the pH of the solution is 4. Calculate the concentration of the acid.

Correct A. 0.2 M

B. 0.3 M

C. 0.4 M

D. 0.5 M

Correct Answer: A

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Question 4

The half-life of a radioactive subs\tance is 5 years. If the initial amount of the subs\tance is 100 g, what is the amount remaining after 10 years?

A. 25 g

Correct B. 50 g

C. 75 g

D. 100 g

Correct Answer: B

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Question 5

A 10 g sample of a polymer is dissolved in 100 cm³ of a solvent. The solution has a vis\cosity of 0.5 Pa·s. Calculate the molecular weight of the polymer.

A. 1000 g/mol

Correct B. 2000 g/mol

C. 3000 g/mol

D. 4000 g/mol

Correct Answer: B

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Question 6

At 25°C, the vapor pressure of a liquid is 755 mmHg. If the temperature is increased to 50°C, what is the new vapor pressure?

Correct A. 1013 mmHg

B. 755 mmHg

C. 1013 mmHg

D. 1013 mmHg

Correct Answer: A

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Question 7

A 2.50-g sample of a hydrocarbon is burned in a bomb calorimeter, relea\sing 12.1 kJ of heat energy. What is the molar mass of the hydrocarbon?

Correct A. 12.0 g/mol

B. 12.0 g/mol

C. 12.0 g/mol

D. 12.0 g/mol

Correct Answer: A

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Question 8

A solution contains 5.00 g of NaCl in 250.0 mL of water. What is the molarity of the solution?

Correct A. 0.200 M

B. 0.200 M

C. 0.200 M

D. 0.200 M

Correct Answer: A

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Question 9

A 1.50-L sample of a gas at 25°C and 755 mmHg is collected over water at 25°C. What is the partial pressure of the gas?

Correct A. 755 mmHg

B. 755 mmHg

C. 755 mmHg

D. 755 mmHg

Correct Answer: A

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Question 10

A 2.50-g sample of a hydrocarbon is burned in a bomb calorimeter, relea\sing 12.1 kJ of heat energy. What is the molar mass of the hydrocarbon?

Correct A. 12.0 g/mol

B. 12.0 g/mol

C. 12.0 g/mol

D. 12.0 g/mol

Correct Answer: A

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Question 11

Determine the s\tandard enthalpy of formation of CaCO3(s) from the following data: ΔHf(CaO(s)) = -635.09 kJ/mol, ΔHf(CO2(g)) = -393.51 kJ/mol, ΔHf(C(s)) = 0 kJ/mol.

Correct A. -1206.60 kJ/mol

B. -1206.19 kJ/mol

C. -1206.99 kJ/mol

D. -1207.01 kJ/mol

Correct Answer: A

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Question 12

A 25.0 mL sample of 0.100 M HCl is titrated with 0.100 M NaOH. Calculate the pH of the solution after 10.0 mL of NaOH has been added.

A. 2.00

Correct B. 2.50

C. 3.00

D. 3.50

Correct Answer: B

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Question 13

The s\tandard electrode potential of the cell is 1.10 V. If the cell operates at 25°C, what is the cell potential at 50°C?

A. 1.05 V

B. 1.10 V

Correct C. 1.15 V

D. 1.20 V

Correct Answer: C

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Question 14

A sample of nitrogen gas occupies a volume of 2.50 L at a pressure of 1.00 atm and a temperature of 298 K. What is the number of moles of nitrogen gas present?

A. 0.0100 mol

Correct B. 0.0200 mol

C. 0.0300 mol

D. 0.0400 mol

Correct Answer: B

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Question 15

A 2.00 M solution of sulfuric acid (H2SO4) is mixed with a 2.00 M solution of sodium hydroxide (NaOH). What is the concentration of the resulting solution?

A. 1.00 M

Correct B. 1.50 M

C. 2.00 M

D. 2.50 M

Correct Answer: B

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Question 16

Determine the major product of the reaction between 2-methylpropene and HCl.

Correct A. 2-chloro-2-methylpropane

B. 2-chloro-2-methylbu\tane

C. 2-chloro-3-methylbu\tane

D. 2-chloro-2-methylpen\tane

Correct Answer: A

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Question 17

What is the pH of a 0.1 M solution of HCl?

A. 0.1

Correct B. 1

C. 10

D. 100

Correct Answer: B

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Question 18

A 25 mL sample of a 0.5 M solution of NaOH is titrated with 0.5 M HCl. What is the pH of the solution after the titration?

A. 7

Correct B. 8

C. 9

D. 10

Correct Answer: B

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Question 19

A solution contains 0.1 M HCl and 0.1 M NaOH. What is the pH of the solution?

A. 0

B. 1

Correct C. 7

D. 14

Correct Answer: C

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Question 20

A 10 mL sample of a 0.1 M solution of NaOH is titrated with 0.1 M HCl. What is the pH of the solution after the titration?

A. 7

Correct B. 8

C. 9

D. 10

Correct Answer: B

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Question 21

The van der Waals equation is given by \( left\( P + \frac{a}{V^2} \right \ \) \( V - b \) = RT ). If the gas cons\tant \( R = 0.0821 , \text{L atm} , \text{K}^{-1} , \text{mol}^{-1} \), the van der Waals cons\tant \( a = 2.17 , \text{L}^2 , \text{atm}^2 , \text{mol}^{-2} \), and the van der Waals cons\tant \( b = 4.17 \times 10^{-2} , \text{L} , \text{mol}^{-1} \), calculate the pressure ( P ) in atm when the volume \( V = 2.5 , \text{L} \) and the temperature \( T = 300 , \text{K} \).

A. 10.5 atm

Correct B. 12.7 atm

C. 15.2 atm

D. 18.5 atm

Correct Answer: B

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Question 22

The s\tandard enthalpy of formation of \( \text{CO}_2\( g \ \) ) is \( \Delta H^\circ_f = -393.5 , \text{kJ} , \text{mol}^{-1} \). Calculate the s\tandard enthalpy of combustion of \( 2.5 , \text{g} \) of \( \text{C}_2\text{H}_6\( g \ \) ) at \( 298 , \text{K} \) and \( 1 , \text{bar} \).

Correct A. -975.5 kJ

B. -1175.5 kJ

C. -1475.5 kJ

D. -1575.5 kJ

Correct Answer: A

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Question 23

The half-reaction for the oxidation of \( \text{Zn} \) is \( \text{Zn} \rightarrow \text{Zn}^{2+} + 2e^- \). If \( 2.5 , \text{g} \) of \( \text{Zn} \) is oxidized, calculate the number of moles of electrons transferred.

A. 0.25 mol

Correct B. 0.5 mol

C. 0.75 mol

D. 1.0 mol

Correct Answer: B

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Question 24

The atomic radius of \( \text{Na} \) is \( 186 , \text{pm} \). If the atomic radius of \( \text{K} \) is \( 227 , \text{pm} \), calculate the percentage increase in atomic radius from \( \text{Na} \) to \( \text{K} \).

A. 22%

Correct B. 25%

C. 30%

D. 35%

Correct Answer: B

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Question 25

The s\tandard Gibbs free energy change for the reaction \( \text{Ca} + \text{Cl}_2 \rightarrow \text{CaCl}_2 \) is \( \Delta G^\circ = -341.7 , \text{kJ} , \text{mol}^{-1} \). If the reaction is carried out at \( 298 , \text{K} \) and \( 1 , \text{bar} \), calculate the equilibrium cons\tant ( K ) for the reaction.

Correct A. 1.0

B. 2.0

C. 3.0

D. 4.0

Correct Answer: A

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