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POST UTME UNIBEN 2021 Chemistry | Objective

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Question 1

Determine the pH of a solution containing 0.1 M HCl and 0.2 M NaOH.

A. 7

B. 8

C. 9

Correct D. 10

Correct Answer: D

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Question 2

Calculate the enthalpy change for the reaction: 2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s). The s\tandard enthalpy of formation of Al2O3 is -1675.7 kJ/mol, and the s\tandard enthalpy of formation of Fe2O3 is -826.4 kJ/mol.

Correct A. -1821.1 kJ/mol

B. -1821.2 kJ/mol

C. -1821.3 kJ/mol

D. -1821.4 kJ/mol

Correct Answer: A

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Question 3

A 25 mL sample of 0.1 M HCl is titrated with 0.2 M NaOH. Calculate the number of moles of NaOH required to reach the equivalence point.

A. 0.005 mol

Correct B. 0.01 mol

C. 0.015 mol

D. 0.02 mol

Correct Answer: B

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Question 4

A polymer has a molecular weight of 50000 g/mol and a degree of polymerization of 100. Calculate the molar mass of the repeating unit.

A. 500 g/mol

Correct B. 5000 g/mol

C. 50000 g/mol

D. 500000 g/mol

Correct Answer: B

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Question 5

A solution contains 0.05 M H2SO4. Calculate the pH of the solution.

A. 1

B. 2

C. 3

Correct D. 4

Correct Answer: D

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Question 6

A 25 cm$^3$ sample of 0.1 M HCl is titrated with 0.1 M NaOH. Calculate the volume of NaOH required to reach the equivalence point.

A. 12.5 cm$^3$

B. 25 cm$^3$

Correct C. 37.5 cm$^3$

D. 50 cm$^3$

Correct Answer: C

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Question 7

The s\tandard enthalpy of formation of CO$$ _2$ $ is -393.5 kJ/mol. Calculate the s\tandard enthalpy of formation of H$$ _2$ $O($l$) if the s\tandard enthalpy of formation of H$$ _2$ $ is -285.8 kJ/mol and the s\tandard enthalpy of formation of O$$ _2$ $ is 0 kJ/mol.

Correct A. -241.8 kJ/mol

B. -285.8 kJ/mol

C. -393.5 kJ/mol

D. -285.8 kJ/mol + 393.5 kJ/mol

Correct Answer: A

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Question 8

The half-life of a radioactive subs\tance is 5 years. If a sample initially contains 100 g of the subs\tance, how much of the subs\tance will remain after 20 years?

Correct A. 12.5 g

B. 25 g

C. 50 g

D. 100 g

Correct Answer: A

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Question 9

A 2.5 g sample of a metal is heated in a Bunsen burner flame. If the temperature of the metal increases by 50°C, what is the specific heat capacity of the metal?

A. 0.1 J/g°C

B. 0.5 J/g°C

Correct C. 1 J/g°C

D. 5 J/g°C

Correct Answer: C

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Question 10

A 10 M solution of HCl is titrated with 1 M NaOH. If 20 cm$^3$ of NaOH is required to reach the equivalence point, what is the volume of HCl in the solution?

A. 10 cm$^3$

Correct B. 20 cm$^3$

C. 40 cm$^3$

D. 80 cm$^3$

Correct Answer: B

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Question 11

Determine the number of moles of electrons transferred during the electrolysis of 2.5 L of 0.5 M H2SO4.

A. 1.25 mol

B. 2.5 mol

Correct C. 5.0 mol

D. 6.25 mol

Correct Answer: C

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Question 12

A 25 mL sample of 0.1 M NaOH is titrated with 0.1 M HCl. Calculate the pH of the solution after 10 mL of HCl has been added.

A. 1.0

Correct B. 2.0

C. 3.0

D. 4.0

Correct Answer: B

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Question 13

The rate cons\tant (k) for a first-order reaction is 0.05 min^-1. If the initial concentration of the reac\tant is 0.1 M, calculate the concentration after 10 minutes.

A. 0.01 M

B. 0.02 M

Correct C. 0.03 M

D. 0.04 M

Correct Answer: C

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Question 14

A sample of a gas has a volume of 2.5 L at a pressure of 1 atm and a temperature of 298 K. Calculate the number of moles of the gas.

A. 0.1 mol

Correct B. 0.2 mol

C. 0.3 mol

D. 0.4 mol

Correct Answer: B

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Question 15

The half-life of a radioactive subs\tance is 5 years. If the initial activity is 1000 Bq, calculate the activity after 10 years.

A. 500 Bq

Correct B. 750 Bq

C. 1000 Bq

D. 1250 Bq

Correct Answer: B

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Question 16

Calculate the s\tandard enthalpy change for the reaction: 2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s). Given that ΔH°(Al2O3) = -1675 kJ/mol, ΔH°(Fe2O3) = -824 kJ/mol, and ΔH°(Fe) = 0 kJ/mol.

Correct A. -2869 kJ/mol

B. -1675 kJ/mol

C. -824 kJ/mol

D. 2869 kJ/mol

Correct Answer: A

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Question 17

A solution containing 0.1 M AgNO3 is electrolyzed u\sing a platinum electrode. If the current is 0.5 A and the time is 2 hours, calculate the mass of silver deposited.

Correct A. 0.05 g

B. 0.1 g

C. 0.15 g

D. 0.2 g

Correct Answer: A

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Question 18

A 10% solution of NaCl is prepared by dissolving 10 g of NaCl in 90 g of water. Calculate the molarity of the solution.

Correct A. 0.1 M

B. 0.5 M

C. 1 M

D. 5 M

Correct Answer: A

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Question 19

A polymer is composed of 80% polyethylene and 20% polypropylene. If the density of polyethylene is 0.95 g/cm^3 and the density of polypropylene is 0.9 g/cm^3, calculate the average density of the polymer.

A. 0.92 g/cm^3

Correct B. 0.95 g/cm^3

C. 0.98 g/cm^3

D. 1.0 g/cm^3

Correct Answer: B

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Question 20

A sample of nitrogen gas is collected over water at a temperature of 25°C and a pressure of 1 atm. If the vapor pressure of water at 25°C is 0.0316 atm, calculate the partial pressure of nitrogen.

Correct A. 0.9684 atm

B. 0.9694 atm

C. 0.97 atm

D. 0.971 atm

Correct Answer: A

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Question 21

The electronegativity of an element is a measure of its ability to attract electrons in a covalent bond. Which of the following elements has the highest electronegativity among the given options?

Correct A. Fluorine (F)

B. Chlorine (Cl)

C. Bromine (Br)

D. Iodine (I)

Correct Answer: A

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Question 22

A sample of an unknown hydrocarbon is found to have a molecular formula of C4H10. Which of the following structures best represents the molecular structure of this hydrocarbon?

Correct A. CH3CH2CH2CH3

B. CH3CH2CH(CH3)2

C. CH3CH2C(CH3)3

D. CH3C(CH3)2CH2CH3

Correct Answer: A

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Question 23

A polymer is a large molecule composed of many repeated subunits called monomers. Which of the following types of polymers is known for its high tensile strength and is often used in the production of textiles?

A. Polyethylene

B. Polypropylene

Correct C. Polyester

D. Polyvinyl Chloride

Correct Answer: C

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Question 24

A metal is an element that is typically hard, shiny, and malleable. Which of the following metals is known for its high melting point and is often used in the production of aircraft parts?

A. Aluminum

B. Copper

Correct C. Ti\tanium

D. Zinc

Correct Answer: C

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Question 25

A biomolecule is a large molecule composed of many smaller subunits called monomers. Which of the following biomolecules is known for its role in energy production and is often found in the mitochondria of cells?

A. DNA

B. RNA

C. Protein

Correct D. ATP

Correct Answer: D

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