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POST UTME BOWEN UNIVERSITY 2025 Chemistry | Objective

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Question 1

Determine the rate cons\tant (k) for the first-order reaction: A → B, given that the initial concentration of A is 0.5 M and the concentration of A after 2 hours is 0.2 M. The rate cons\tant is related to the half-life \( t1/2 \) by the equation: ln(2) = kt1/2.

Correct A. \( k = \frac{ln\( 2 \ \)}{t_{1/2}} )

B. \( k = \frac{ln\( 0.2 \ \)}{2} )

C. \( k = \frac{0.5 - 0.2}{2} \)

D. \( k = \frac{0.2}{0.5} \)

Correct Answer: A

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Question 2

A 2.5 M solution of HCl is electrolyzed u\sing a platinum electrode. If the electrolysis is carried out for 2 hours, and the volume of H2 gas produced is 2.5 L at 25°C and 1 atm, calculate the number of moles of H2 gas produced.

A. \( n = \frac{PV}{RT} \)

Correct B. \( n = \frac{V}{22.4} \)

C. \( n = \frac{2.5}{22.4} \)

D. \( n = \frac{2.5 \times 1}{22.4} \)

Correct Answer: B

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Question 3

A polymer is composed of repeating units of the following structure: CH2-CH2-CH2-CH2. If the polymer has a molecular weight of 100,000 g/mol, and the repeating unit has a molecular weight of 28 g/mol, calculate the degree of polymerization (DP).

Correct A. \( DP = \frac{M_n}{M_0} \)

B. \( DP = \frac{M_0}{M_n} \)

C. \( DP = \frac{M_n}{M_0 \times 28} \)

D. \( DP = \frac{28}{M_n} \)

Correct Answer: A

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Question 4

A solution of 0.1 M NaCl is prepared by dissolving 1.0 g of NaCl in 100 mL of water. If the density of the solution is 1.0 g/mL, calculate the concentration of NaCl in the solution.

Correct A. \( C = \frac{m}{V} \)

B. \( C = \frac{V}{m} \)

C. \( C = \frac{m}{V \times d} \)

D. \( C = \frac{V \times d}{m} \)

Correct Answer: A

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Question 5

A gas is collected over water at 25°C and 1 atm. If the volume of the gas is 2.5 L, and the vapor pressure of water at 25°C is 0.0313 atm, calculate the partial pressure of the gas.

Correct A. \( P_{gas} = P_{total} - P_{H2O} \)

B. \( P_{gas} = P_{total} + P_{H2O} \)

C. \( P_{gas} = \frac{P_{total} - P_{H2O}}{2} \)

D. \( P_{gas} = \frac{P_{total} + P_{H2O}}{2} \)

Correct Answer: A

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Question 6

Determine the pH of a 0.1 M solution of HCl.

A. 1

B. 2

C. 3

Correct D. 4

Correct Answer: D

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Question 7

A 25 mL sample of 0.5 M H2SO4 is titrated with 1 M NaOH. Calculate the number of moles of NaOH required to reach the equivalence point.

A. 0.025

Correct B. 0.05

C. 0.075

D. 0.1

Correct Answer: B

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Question 8

The s\tandard enthalpy of formation of CO2(g) is -393.5 kJ/mol. Calculate the s\tandard enthalpy of formation of H2CO3(s) given that the s\tandard enthalpy of formation of H2O(l) is -285.8 kJ/mol and the s\tandard enthalpy of formation of CO(g) is -110.5 kJ/mol.

A. -685.8

Correct B. -695.8

C. -705.8

D. -715.8

Correct Answer: B

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Question 9

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

A. 200

B. 400

Correct C. 600

D. 800

Correct Answer: C

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Question 10

A 1 M solution of NaOH is titrated with 1 M HCl. Calculate the pH of the solution at the equivalence point.

A. 7

B. 8

C. 9

Correct D. 10

Correct Answer: D

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Question 11

Determine the number of moles of ΔH2O formed when 2.50 g of H2SO4 reacts with 3.00 g of NaOH in a reaction that proceeds to completion.

A. 0.0500 mol

Correct B. 0.0750 mol

C. 0.100 mol

D. 0.125 mol

Correct Answer: B

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Question 12

A 2.00-L sample of a gas at 25°C and 1.00 atm is collected over water at 25°C. If the vapor pressure of water at 25°C is 23.8 torr, what is the partial pressure of the gas?

A. 0.970 atm

B. 0.975 atm

Correct C. 0.980 atm

D. 0.985 atm

Correct Answer: C

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Question 13

A 2.50-g sample of a compound containing only C, H, and O is analyzed by combustion. The CO2 produced is 1.25 g, and the H2O produced is 0.500 g. What is the empirical formula of the compound?

Correct A. C2H4O2

B. C2H6O

C. C3H6O

D. C4H8O2

Correct Answer: A

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Question 14

A 1.00-L sample of a solution containing 0.100 M NaCl is mixed with 1.00 L of a solution containing 0.0500 M CaCl2. 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 15

A 2.00-g sample of a subs\tance is placed in a 100-mL flask and heated to 100°C. The pressure of the gas is measured to be 1.00 atm. What is the number of moles of gas present?

A. 0.0500 mol

B. 0.0750 mol

Correct C. 0.100 mol

D. 0.125 mol

Correct Answer: C

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Question 16

The s\tandard enthalpy of formation of CO2(g) is -393.5 kJ/mol. Calculate the s\tandard enthalpy of formation of CaCO3(s) if the s\tandard enthalpy of formation of CaO(s) is -635.09 kJ/mol and that of C(s) is 0 kJ/mol.

A. -1207.59 kJ/mol

B. -1207.59 kJ/mol

C. -1207.59 kJ/mol

Correct D. -1207.59 kJ/mol

Correct Answer: D

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Question 17

The half-reaction for the reduction of Cu2+ to Cu is: Cu2+ + e- → Cu+ + ?

Correct A. Cu

B. Cu2+

C. e-

D. H+

Correct Answer: A

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Question 18

The s\tandard enthalpy of formation of H2O(l) is -285.83 kJ/mol. Calculate the s\tandard enthalpy of combustion of 1 mole of C(s) if the s\tandard enthalpy of formation of CO2(g) is -393.5 kJ/mol.

A. -393.5 kJ/mol

B. -393.5 kJ/mol

C. -393.5 kJ/mol

Correct D. -393.5 kJ/mol

Correct Answer: D

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Question 19

The half-reaction for the oxidation of S2- to S is: S2- → S + ?

A. 2e-

Correct B. e-

C. H2O

D. OH-

Correct Answer: B

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Question 20

The s\tandard enthalpy of formation of NH3(g) is -45.9 kJ/mol. Calculate the s\tandard enthalpy of formation of N2H4(l) if the s\tandard enthalpy of formation of N2(g) is 0 kJ/mol and that of H2(g) is 0 kJ/mol.

A. -50.6 kJ/mol

B. -50.6 kJ/mol

C. -50.6 kJ/mol

Correct D. -50.6 kJ/mol

Correct Answer: D

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