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POST UTME UNIBEN 2025 Chemistry | Objective

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Question 1

Determine the number of moles of CO2 produced when 2.5 g of calcium carbonate (CaCO3) is completely decomposed at cons\tant pressure and temperature.

A. 0.05 mol

Correct B. 0.10 mol

C. 0.15 mol

D. 0.20 mol

Correct Answer: B

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Question 2

What is the major product of the reaction between 2-methylpropane and chlorine?

Correct A. 2-chloro-2-methylpropane

B. 2-chloro-2-methyl-1-propane

C. 2-chloro-1-methylpropane

D. 2-chloro-1-methyl-2-propane

Correct Answer: A

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Question 3

A polymer has a molecular weight of 50,000 g/mol and a degree of polymerization of 500. What is the molar mass of the repeating unit?

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 4

What is the oxidation state of sulfur in the compound SO2Cl2?

A. +4

B. +2

Correct C. +6

D. +8

Correct Answer: C

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Question 5

A 2.5 M solution of HCl is electrolyzed u\sing a platinum electrode. What is the mass of Cl2 gas produced at the anode in 2 hours?

A. 0.25 g

B. 0.50 g

Correct C. 1.00 g

D. 2.00 g

Correct Answer: C

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Question 6

A 25.0 mL sample of 0.100 M HCl is titrated with 0.100 M NaOH. Calculate the pH of the solution after the addition of 25.0 mL of NaOH.

A. 2.00

Correct B. 3.00

C. 4.00

D. 5.00

Correct Answer: B

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Question 7

A polymer has a molecular weight of 50,000 g/mol and a degree of polymerization of 500. What is the molar mass of the repeating unit?

Correct A. 100

B. 200

C. 500

D. 1000

Correct Answer: A

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Question 8

A 2.00 g sample of a metal oxide is heated in a crucible until it is completely reduced to the metal. If the mass of the metal is 1.50 g, what is the percentage of the metal in the original oxide?

A. 75.0

B. 80.0

Correct C. 85.0

D. 90.0

Correct Answer: C

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Question 9

A 25.0 mL sample of 0.100 M HCl is titrated with 0.100 M NaOH. Calculate the number of moles of NaOH required to reach the equivalence point.

A. 0.0025

Correct B. 0.0050

C. 0.0075

D. 0.0100

Correct Answer: B

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Question 10

A 2.00 g sample of a metal oxide is heated in a crucible until it is completely reduced to the metal. If the mass of the metal is 1.50 g, what is the molar mass of the metal?

A. 50.0

B. 75.0

Correct C. 100.0

D. 150.0

Correct Answer: C

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Question 11

The atomic radius of an atom is defined as the dis\tance from the nucleus to the outermost electron in a neutral atom. Which of the following statements is true about the atomic radius of an atom?

A. The atomic radius of an atom decreases as the atomic number increases.

Correct B. The atomic radius of an atom increases as the atomic number increases.

C. The atomic radius of an atom remains cons\tant for all elements.

D. The atomic radius of an atom is indep\endent of the atomic number.

Correct Answer: B

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Question 12

A redox reaction involves the transfer of electrons from one species to another. Which of the following is an example of a redox reaction?

A. 2Na + Cl2 → 2NaCl

B. 2H2 + O2 → 2H2O

Correct C. Zn + CuSO4 → ZnSO4 + Cu

D. Fe + CuSO4 → FeSO4 + Cu

Correct Answer: C

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Question 13

The boiling point of a subs\tance is the temperature at which the vapor pressure of the subs\tance equals the surrounding pressure. Which of the following is an example of a subs\tance with a high boiling point?

Correct A. H2O

B. CO2

C. CH4

D. O2

Correct Answer: A

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Question 14

The rate of a chemical reaction is affected by several factors, including the concentration of reac\tants, temperature, and surface area. Which of the following is an example of a factor that increases the rate of a chemical reaction?

Correct A. Increa\sing the concentration of reac\tants

B. Decrea\sing the temperature

C. Increa\sing the surface area of reac\tants

D. Decrea\sing the pressure

Correct Answer: A

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Question 15

The equilibrium cons\tant (Kc) is a measure of the extent to which a chemical reaction proceeds. Which of the following is an example of a reaction with a high equilibrium cons\tant (Kc)?

A. N2 + O2 → 2NO

Correct B. 2H2 + O2 → 2H2O

C. CaCO3 → CaO + CO2

D. H2 + I2 → 2HI

Correct Answer: B

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Question 16

The solubility of a subs\tance is the maximum amount of the subs\tance that can dissolve in a given amount of solvent at a particular temperature. Which of the following is an example of a subs\tance with a high solubility?

Correct A. NaCl

B. CaCO3

C. H2O

D. CO2

Correct Answer: A

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Question 17

The pH of a solution is a measure of its acidity or basicity. Which of the following is an example of a solution with a high pH?

A. HCl

Correct B. NaOH

C. H2SO4

D. H3PO4

Correct Answer: B

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Question 18

The molarity of a solution is a measure of the concentration of solute particles in a given amount of solvent. Which of the following is an example of a solution with a high molarity?

A. 0.1 M NaCl

B. 0.5 M HCl

C. 1.0 M NaOH

Correct D. 2.0 M H2SO4

Correct Answer: D

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Question 19

The density of a subs\tance is the mass per unit volume of the subs\tance. Which of the following is an example of a subs\tance with a high density?

A. H2O

B. CO2

C. CH4

D. O2

Correct Answer: VIEW ANSWER

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Question 20

The entropy change (ΔS) for a reaction is given by the equation ΔS = ΔH/T. If the enthalpy change (ΔH) for a reaction is -120 kJ/mol and the temperature (T) is 298 K, calculate the entropy change (ΔS) in J/mol·K.

A. 400 J/mol·K

B. 500 J/mol·K

Correct C. 600 J/mol·K

D. 700 J/mol·K

Correct Answer: C

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Question 21

A polymer is formed from the condensation reaction of two monomers, A and B. The molecular weight of the polymer is 100,000 g/mol. If the molecular weights of monomers A and B are 50,000 g/mol and 30,000 g/mol, respectively, calculate the number of monomer units in the polymer.

A. 200

Correct B. 250

C. 300

D. 350

Correct Answer: B

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Question 22

The s\tandard enthalpy of formation (ΔH°f) for a compound is given by the equation ΔH°f = ΔH°f(A) + ΔH°f(B) - ΔH°f(AB). If the s\tandard enthalpy of formation for compound A is -50 kJ/mol, compound B is -30 kJ/mol, and the s\tandard enthalpy of formation for the compound AB is -80 kJ/mol, calculate the s\tandard enthalpy of formation for the compound AB.

A. -40 kJ/mol

B. -50 kJ/mol

Correct C. -60 kJ/mol

D. -70 kJ/mol

Correct Answer: C

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Question 23

A gas is confined to a container with a volume of 2.5 L. If the temperature of the gas is increased from 20°C to 50°C, calculate the new volume of the gas, assuming the pressure remains cons\tant.

A. 3.5 L

Correct B. 4.0 L

C. 4.5 L

D. 5.0 L

Correct Answer: B

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Question 24

A solution contains 2.5 g of sodium chloride (NaCl) dissolved in 100 mL of water. If the density of the solution is 1.2 g/mL, calculate the molarity of the solution.

A. 0.1 M

Correct B. 0.2 M

C. 0.3 M

D. 0.4 M

Correct Answer: B

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Question 25

A sample of hydrogen gas (H2) is collected over water at a temperature of 20°C and a pressure of 1 atm. If the volume of the gas is 2.5 L, calculate the partial pressure of the hydrogen gas.

A. 0.5 atm

B. 0.6 atm

Correct C. 0.7 atm

D. 0.8 atm

Correct Answer: C

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