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POST UTME UNILORIN 2017 Chemistry | Objective

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Question 1

A 2.5g sample of a non-volatile solute is dissolved in 50g of water at 25°C. Calculate the molality of the 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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Question 2

A gas at 300K and 1 atm expands to occupy a volume of 5.6L. Calculate the work done by the gas.

Correct A. -2.5 J

B. -1.25 J

C. 1.25 J

D. 2.5 J

Correct Answer: A

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Question 3

The reaction between sodium hydroxide and hydrochloric acid is represented by the equation: NaOH + HCl → NaCl + H2O. Calculate the number of moles of HCl required to react with 2.5 moles of NaOH.

Correct A. 1.25 mol

B. 2.5 mol

C. 3.75 mol

D. 5.0 mol

Correct Answer: A

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Question 4

A 2.0L sample of a gas at 27°C and 1 atm is collected over water at 27°C. Calculate the partial pressure of the gas.

A. 0.95 atm

Correct B. 0.98 atm

C. 1.02 atm

D. 1.05 atm

Correct Answer: B

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Question 5

A 1.5g sample of a non-volatile solute is dissolved in 50g of water at 25°C. Calculate the mole \fraction of the solute.

A. 0.025

Correct B. 0.050

C. 0.075

D. 0.100

Correct Answer: B

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Question 6

Determine the s\tandard Gibbs free energy change (ΔG°) for the reaction: 2NO(g) + O2(g) → 2NO2(g) at 298 K and 1 atm, given that the s\tandard enthalpy change (ΔH°) is -114.1 kJ/mol and the s\tandard entropy change (ΔS°) is -146.4 J/mol·K.

A. -114.1 kJ/mol

B. -146.4 J/mol·K

C. -114.1 kJ/mol + 298 K * \( -146.4 J/mol·K \)

Correct D. -114.1 kJ/mol - 298 K * \( -146.4 J/mol·K \)

Correct Answer: D

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Question 7

A 0.500 M solution of sodium hydroxide (NaOH) is prepared by dissolving 25.0 g of NaOH in water and diluting to a total volume of 1.00 L. Calculate the concentration of hydroxide ions \( OH- \) in the solution.

Correct A. 0.500 M

B. 0.250 M

C. 1.00 M

D. 2.00 M

Correct Answer: A

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Question 8

A sample of a metal (M) reacts with chlorine gas (Cl2) to form a white solid. The reaction is as follows: M + Cl2 → MCl2. If 2.50 g of the metal reacts with 1.00 g of Cl2, what is the molar mass of the metal?

A. 50.0 g/mol

Correct B. 75.0 g/mol

C. 100 g/mol

D. 125 g/mol

Correct Answer: B

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Question 9

A 2.00 M solution of hydrogen peroxide (H2O2) is prepared by dissolving 40.0 g of H2O2 in water and diluting to a total volume of 1.00 L. Calculate the concentration of hydrogen ions \( H+ \) in the solution.

A. 1.00 M

Correct B. 2.00 M

C. 4.00 M

D. 8.00 M

Correct Answer: B

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Question 10

A sample of a non-metal (X) reacts with oxygen gas (O2) to form a white solid. The reaction is as follows: X + O2 → XO2. If 1.50 g of the non-metal reacts with 2.00 g of O2, what is the molar mass of the non-metal?

A. 25.0 g/mol

B. 50.0 g/mol

Correct C. 75.0 g/mol

D. 100 g/mol

Correct Answer: C

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Question 11

Determine the number of moles of oxygen gas (O2) produced at STP when 2.50 g of potassium chlorate (KClO3) decomposes according to the equation: 2KClO3(s) → 2KCl(s) + 3O2(g).

A. 0.050 mol

Correct B. 0.100 mol

C. 0.150 mol

D. 0.200 mol

Correct Answer: B

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Question 12

A 25.0 mL sample of 0.100 M NaOH is titrated with 0.0500 M HCl. What is the pH of the solution after the reaction is complete?

A. 3.00

B. 4.00

Correct C. 5.00

D. 6.00

Correct Answer: C

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Question 13

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 g/mol

B. 200 g/mol

C. 50 g/mol

D. 25 g/mol

Correct Answer: A

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Question 14

A solution contains 0.100 M NH3 and 0.0500 M HCl. What is the pH of the solution?

A. 4.00

B. 5.00

C. 6.00

Correct D. 7.00

Correct Answer: D

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Question 15

A 10.0 mL sample of 0.100 M CaCl2 is mixed with 20.0 mL of 0.0500 M NaOH. What is the concentration of the resulting solution?

A. 0.0500 M

Correct B. 0.0750 M

C. 0.100 M

D. 0.125 M

Correct Answer: B

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Question 16

The atomic radius of an element in a particular period increases as you move from left to right in the periodic table. Which of the following is a correct explanation for this tr\end?

A. The atomic radius increases due to the increase in the number of energy levels.

Correct B. The atomic radius increases due to the decrease in the effective nuclear charge.

C. The atomic radius increases due to the increase in the number of electrons in the outermost energy level.

D. The atomic radius increases due to the increase in the atomic mass.

Correct Answer: B

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Question 17

A 0.1 M solution of a weak acid HA has a pH of 3.5. What is the concentration of the hydrogen ions in the solution?

Correct A. 1.0 x 10^-4 M

B. 1.0 x 10^-3 M

C. 1.0 x 10^-2 M

D. 1.0 x 10^-1 M

Correct Answer: A

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Question 18

The diagram below shows a titration curve for the reaction between a strong acid and a weak base. What is the pH of the solution at point A?

A. 7.0

Correct B. 8.0

C. 9.0

D. 10.0

Correct Answer: B

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Question 19

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 monomer?

A. 200 g/mol

Correct B. 400 g/mol

C. 600 g/mol

D. 800 g/mol

Correct Answer: B

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Question 20

A solution of a salt has a conductivity of 1.0 x 10^-3 S/m. What is the concentration of the salt in the solution?

A. 0.1 M

Correct B. 0.5 M

C. 1.0 M

D. 5.0 M

Correct Answer: B

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Question 21

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

A. 0.05 M

Correct B. 0.025 M

C. 0.1 M

D. 0.5 M

Correct Answer: B

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Question 22

A solution contains 0.5 M NaCl. If 10 mL of 1 M HCl is added to 90 mL of the solution, what is the concentration of Cl^- ions in the resulting solution?

Correct A. 0.55 M

B. 0.5 M

C. 0.45 M

D. 0.4 M

Correct Answer: A

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Question 23

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. -283.5 kJ/mol

Correct Answer: A

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Question 24

A sample of a gas occupies 250 mL at 27°C and 1 atm. What is the volume of the gas at 37°C and 2 atm?

Correct A. 375 mL

B. 250 mL

C. 125 mL

D. 500 mL

Correct Answer: A

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Question 25

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

A. 250 Bq

Correct B. 500 Bq

C. 1000 Bq

D. 2000 Bq

Correct Answer: B

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