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POST UTME UNILORIN 2020 Chemistry | Objective

Are you preparing for POST UTME UNILORIN exams? Reviewing past questions is one of the most effective ways to guarantee a high score. This practice hub features authentic 2020 Chemistry (Objective) questions designed to simulate the real exam environment.

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Question 1

A 2.50-g sample of a polymer is dissolved in 50.0 mL of a solvent. If the polymer has a molar mass of 1.50 x 10^5 g/mol and the density of the solution is 1.20 g/mL, calculate the number of moles of polymer present in the solution.

Correct A. 0.0170 mol

B. 0.0175 mol

C. 0.0180 mol

D. 0.0185 mol

Correct Answer: A

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Question 2

A 2.00 M solution of HCl is titrated with a 1.00 M solution of NaOH. If 25.0 mL of NaOH is required to reach the equivalence point, calculate the number of moles of HCl present in the original solution.

Correct A. 0.0500 mol

B. 0.0505 mol

C. 0.0510 mol

D. 0.0515 mol

Correct Answer: A

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Question 3

A 1.00-g sample of a polymer is dissolved in 100.0 mL of a solvent. If the polymer has a molar mass of 3.00 x 10^4 g/mol and the density of the solution is 1.10 g/mL, calculate the number of moles of polymer present in the solution.

Correct A. 0.0333 mol

B. 0.0335 mol

C. 0.0337 mol

D. 0.0339 mol

Correct Answer: A

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Question 4

A 2.00 M solution of HCl is titrated with a 1.00 M solution of NaOH. If 30.0 mL of NaOH is required to reach the equivalence point, calculate the number of moles of HCl present in the original solution.

Correct A. 0.0600 mol

B. 0.0605 mol

C. 0.0610 mol

D. 0.0615 mol

Correct Answer: A

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Question 5

A 1.50-g sample of a polymer is dissolved in 50.0 mL of a solvent. If the polymer has a molar mass of 2.00 x 10^5 g/mol and the density of the solution is 1.20 g/mL, calculate the number of moles of polymer present in the solution.

Correct A. 0.00750 mol

B. 0.00755 mol

C. 0.00760 mol

D. 0.00765 mol

Correct Answer: A

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Question 6

Determine the number of moles of ethane (C2H6) produced from 2.5 moles of ethene (C2H4) in the following reaction: C2H4 + H2 → C2H6

A. 1.25 moles

B. 2.5 moles

Correct C. 3.75 moles

D. 5 moles

Correct Answer: C

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Question 7

Calculate the s\tandard enthalpy change (ΔH°) for the reaction: 2Al(s) + 3H2O(l) → 2Al(OH)3(s) + 3H2(g) given that ΔH° for the formation of Al(OH)3 is -3265.6 kJ/mol and ΔH° for the formation of H2 is 0 kJ/mol

A. -3265.6 kJ/mol

Correct B. -3265.6 kJ/mol + 3\( 0 kJ/mol \)

C. -3265.6 kJ/mol + 3\( 0 kJ/mol \)

D. -3265.6 kJ/mol + 3\( 0 kJ/mol \)

Correct Answer: B

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Question 8

A sample of a polymer has a molecular weight of 50000 g/mol. If 2.5 g of the polymer is dissolved in 50 mL of a solvent, calculate the concentration of the solution in g/mL

A. 0.1 g/mL

Correct B. 0.5 g/mL

C. 1 g/mL

D. 5 g/mL

Correct Answer: B

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Question 9

A diagram of a titration setup is shown below. If 25 mL of 0.1 M NaOH is required to neutralize 20 mL of a weak acid, calculate the concentration of the acid

A. 0.05 M

Correct B. 0.1 M

C. 0.2 M

D. 0.5 M

Correct Answer: B

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Question 10

A diagram of a cell is shown below. Identify the part labeled A

Correct A. Mitochondria

B. Nucleus

C. Ribosome

D. Lysosome

Correct Answer: A

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Question 11

The rate cons\tant of a first-order reaction is given by the equation \( k = Ae^{-E_a/RT} \). If the activation energy \( E_a \) is 100 kJ/mol, the gas cons\tant ( R ) is 8.314 J/\( mol*K \), and the temperature ( T ) is 300 K, what is the value of the pre-exponential factor ( A ) if the rate cons\tant ( k ) is 0.05 s\( ^{-1} \)?

Correct A. \( 1.23 \times 10^{10} \)

B. \( 1.23 \times 10^{12} \)

C. \( 1.23 \times 10^{14} \)

D. \( 1.23 \times 10^{16} \)

Correct Answer: A

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Question 12

A 0.1 M solution of a weak acid ( HA ) is titrated with 0.1 M ( NaOH ). If the initial pH of the solution is 4.5, what is the pH of the solution after the addition of 20 mL of ( NaOH )?

A. 4.8

Correct B. 5.2

C. 5.5

D. 6.0

Correct Answer: B

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Question 13

A polymer has a molecular weight of 100,000 g/mol and a degree of polymerization of 500. What is the molar mass of the repeating unit of the polymer?

A. 200 g/mol

B. 400 g/mol

Correct C. 500 g/mol

D. 600 g/mol

Correct Answer: C

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Question 14

A redox reaction involves the oxidation of \( Fe^{2+} \) to \( Fe^{3+} \) and the reduction of \( MnO_4^- \) to \( Mn^{2+} \). What is the oxidation number of manganese in \( MnO_4^- \)?

A. +2

B. +4

Correct C. +6

D. +8

Correct Answer: C

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Question 15

A metal is extracted from its ore through the electrolysis of a molten salt. If the metal has a s\tandard electrode potential of -1.2 V and the electrolysis is carried out at a current density of 100 A/m\( ^2 \), what is the mass of the metal deposited per unit area of the electrode?

A. 0.1 g/m\( ^2 \)

Correct B. 1.0 g/m\( ^2 \)

C. 10 g/m\( ^2 \)

D. 100 g/m\( ^2 \)

Correct Answer: B

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Question 16

The electrolysis of a solution of copper(II) sulfate u\sing a copper electrode results in the formation of copper metal and oxygen gas. Write a balanced equation for the reaction.

Correct A. Cu^{2+} + 2e^{-} → Cu + O_{2}

B. Cu + 2e^{-} → Cu^{2+} + O_{2}

C. Cu^{2+} + 2e^{-} → Cu + H_{2}O

D. Cu + 2e^{-} → Cu^{2+} + H_{2}O

Correct Answer: A

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Question 17

A metal M reacts with chlorine gas to form a white solid. The reaction is as follows: M + Cl_{2} → MCl_{2}. Identify the metal M.

A. Na

B. K

Correct C. Ca

D. Mg

Correct Answer: C

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Question 18

The half-reaction for the reduction of oxygen gas is: O_{2} + 4H^{+} + 4e^{-} → 2H_{2}O. What is the oxidation number of oxygen in the product?

Correct A. -2

B. +2

C. +1

D. -1

Correct Answer: A

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Question 19

A solution of sodium hydroxide is titrated with a solution of hydrochloric acid. The reaction is as follows: NaOH + HCl → NaCl + H_{2}O. What is the pH of the solution after the reaction is complete?

Correct A. 7

B. 9

C. 11

D. 13

Correct Answer: A

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Question 20

A metal M reacts with oxygen gas to form a white solid. The reaction is as follows: 4M + 3O_{2} → 2M_{2}O_{3}. Identify the metal M.

Correct A. Al

B. Fe

C. Cu

D. Zn

Correct Answer: A

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Question 21

The atomic radius of an element in the periodic table decreases as you move from left to right across a period. Which of the following elements has an atomic radius that is closest to that of carbon?

A. Boron (B)

Correct B. Nitrogen (N)

C. Oxygen (O)

D. Fluorine (F)

Correct Answer: B

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Question 22

A solution of 0.5 M NaCl is prepared by dissolving 25.0 g of NaCl in 1.0 L of water. What is the concentration of Na+ ions in the solution?

Correct A. 0.25 M

B. 0.5 M

C. 0.75 M

D. 1.0 M

Correct Answer: A

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Question 23

The reaction between nitrogen and oxygen to form nitrogen dioxide is a first-order reaction with respect to nitrogen. If the initial concentration of nitrogen is 0.1 M and the rate cons\tant is 0.05 min^-1, what is the concentration of nitrogen after 10 minutes?

A. 0.05 M

Correct B. 0.075 M

C. 0.1 M

D. 0.125 M

Correct Answer: B

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Question 24

The s\tandard enthalpy of formation of CO2(g) is -393.5 kJ/mol. What is the s\tandard enthalpy of formation of CO(g)?

Correct A. -110.5 kJ/mol

B. -393.5 kJ/mol

C. -74.8 kJ/mol

D. -285.8 kJ/mol

Correct Answer: A

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Question 25

The reaction between sulfuric acid and sodium hydroxide is a neutralization reaction. If 25.0 mL of 1.0 M H2SO4 is mixed with 25.0 mL of 1.0 M NaOH, what is the concentration of the resulting solution?

A. 0.5 M

Correct B. 1.0 M

C. 1.5 M

D. 2.0 M

Correct Answer: B

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