POST UTME OAU 2025 Chemistry | Objective

Practice these randomly selected questions to test your readiness.

Question 1
A sample of H2 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 23.8 mmHg, what is the partial pressure of H2?
A. 736.2 mmHg
B. 712.4 mmHg
C. 688.6 mmHg
D. 664.8 mmHg
Question 2
A 0.50 M solution of HCl is prepared by dissolving 4.0 g of HCl in water to make 1 L of solution. What is the concentration of H+ ions in the solution?
A. 0.11 M
B. 0.22 M
C. 0.33 M
D. 0.44 M
Question 3
A sample of an ideal gas at 25°C and 1 atm is heated to 50°C at cons\tant pressure. Calculate the ratio of the final volume to the initial volume.
A. 2
B. 1
C. 1/2
D. 1/4
Question 4
The half-life of a radioactive subs\tance is 5.00 years. If 100.0 g of the subs\tance initially exists, what is the mass remaining after 20.0 years?
A. 12.5
B. 25.0
C. 50.0
D. 100.0
Question 5
The reaction of nitrogen dioxide with water produces nitric acid and nitric oxide. Write the balanced chemical equation for this reaction, including the states of the reac\tants and products.
A. 4NO2(g) + 2H2O(l) → 4HNO3(aq) + O2(g)
B. 2NO2(g) + 2H2O(l) → 2HNO3(aq) + O2(g)
C. 4NO2(g) + 2H2O(l) → 4HNO3(aq)
D. 2NO2(g) + 2H2O(l) → 2HNO3(aq)
Question 6
The s\tandard enthalpy of formation of CO2(g) is -393.5 kJ/mol. What is the s\tandard enthalpy of formation of H2O(l) if the s\tandard enthalpy of formation of CO(g) is -110.5 kJ/mol and the s\tandard enthalpy of formation of H2(g) is 0 kJ/mol?
A. -285.8 kJ/mol
B. -285.9 kJ/mol
C. -286.0 kJ/mol
D. -286.1 kJ/mol
Question 7
A sample of O2 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 23.8 mmHg, what is the partial pressure of O2?
A. 736.2 mmHg
B. 712.4 mmHg
C. 688.6 mmHg
D. 664.8 mmHg
Question 8
A 1.0 M solution of NaOH is prepared by dissolving 40 g of NaOH in 1000 mL of water. Calculate the pOH of the solution.
A. 13.0
B. 14.0
C. 15.0
D. 16.0
Question 9
The diagram below shows a circuit setup. Identify the part labeled A.
A. Resistor
B. Battery
C. Switch
D. Ammeter
Question 10
A solution contains 0.2 M NaOH and 0.1 M HCl. What is the pH of the solution after the reaction is complete?
A. 1
B. 2
C. 3
D. 4
Question 11
A 2.5 g sample of a polymer is dissolved in 50 mL of a solvent. If the density of the solution is 1.2 g/mL, what is the molar mass of the polymer?
A. 100 g/mol
B. 200 g/mol
C. 500 g/mol
D. 1000 g/mol
Question 12
The s\tandard reduction potential of the Mn2+/Mn couple is -1.18 V. What is the s\tandard reduction potential of the Mn3+/Mn couple?
A. -0.90 V
B. -1.18 V
C. -1.50 V
D. -2.00 V
Question 13
A 0.5 M solution of H2SO4 is prepared by dissolving 9.0 g of H2SO4 in water to make 1 L of solution. What is the concentration of H+ ions in the solution?
A. 0.18 M
B. 0.36 M
C. 0.54 M
D. 0.72 M
Question 14
Determine the number of moles of $\text{O}_2$ that react with 2.50 moles of $\text{H}_2$ in the reaction $\text{H}_2 + \frac{1}{2}\text{O}_2 \rightarrow \text{H}_2\text{O}$
A. 1.25
B. 2.50
C. 3.75
D. 5.00
Question 15
A sample of CO2 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 23.8 mmHg, what is the partial pressure of CO2?
A. 760 mmHg
B. 736.2 mmHg
C. 712.4 mmHg
D. 688.6 mmHg

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