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POST UTME PAN-ATLANTIC UNIVERSITY 2025 Chemistry | Objective

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Question 1

Calculate the s\tandard enthalpy change \( ΔH^circ \) for the reaction: 2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s). The s\tandard enthalpy of formation \( ΔH^circ_f \) values are: ΔH^circ_f(Al2O3(s)) = -1675.7 kJ/mol, ΔH^circ_f(Al(s)) = 0 kJ/mol, ΔH^circ_f(Fe(s)) = 0 kJ/mol, and ΔH^circ_f(Fe2O3(s)) = -824.2 kJ/mol.

A. 0 kJ/mol

Correct B. -1675.7 kJ/mol

C. 1675.7 kJ/mol

D. 824.2 kJ/mol

Correct Answer: B

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Question 2

A 2.50 M solution of HCl is titrated with 0.500 M NaOH. What is the pH of the solution after the addition of 25.0 mL of NaOH?

A. 1.00

Correct B. 2.00

C. 3.00

D. 4.00

Correct Answer: B

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Question 3

A metal (M) reacts with oxygen to form a basic oxide (MO). The reaction is: 4M + 3O2 → 2MO. If 2.50 g of M reacts with 1.50 g of O2, what is the mass of MO formed?

A. 3.75 g

B. 4.25 g

Correct C. 5.00 g

D. 6.25 g

Correct Answer: C

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Question 4

A 1.00 M solution of H2SO4 is titrated with 0.500 M NaOH. What is the pH of the solution after the addition of 20.0 mL of NaOH?

A. 1.00

Correct B. 2.00

C. 3.00

D. 4.00

Correct Answer: B

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Question 5

A metal (M) reacts with oxygen to form a basic oxide (MO). The reaction is: 4M + 3O2 → 2MO. If 2.50 g of M reacts with 1.50 g of O2, what is the mass of M used?

Correct A. 2.50 g

B. 3.75 g

C. 4.25 g

D. 5.00 g

Correct Answer: A

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Question 6

Determine the s\tandard enthalpy of formation of CaCO3(s) from the following data: ΔH°f(CaO(s)) = -635.09 kJ/mol, ΔH°f(CO2(g)) = -393.51 kJ/mol, ΔH°f(Ca(s)) = -178.2 kJ/mol.

Correct A. -1206.7 kJ/mol

B. -1206.8 kJ/mol

C. -1206.9 kJ/mol

D. -1207.0 kJ/mol

Correct Answer: A

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Question 7

A 0.500 M solution of HCl is titrated with 0.500 M NaOH. What is the pH of the solution after 25.0 mL of NaOH has been added?

A. 2.00

Correct B. 2.50

C. 3.00

D. 3.50

Correct Answer: B

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Question 8

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

Correct A. C2H4O2

B. C2H6O

C. C3H6O

D. C3H8O

Correct Answer: A

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Question 9

A 1.00 M solution of NaOH is titrated with 1.00 M HCl. What is the pH of the solution after 50.0 mL of HCl has been added?

A. 1.00

Correct B. 2.00

C. 3.00

D. 4.00

Correct Answer: B

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Question 10

A 0.500 M solution of H2SO4 is titrated with 0.500 M NaOH. What is the pH of the solution after 25.0 mL of NaOH has been added?

A. 1.00

Correct B. 2.00

C. 3.00

D. 4.00

Correct Answer: B

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Question 11

In a reaction between sodium (Na) and chlorine (Cl2), what is the expected product?

Correct A. Sodium chloride (NaCl)

B. Sodium oxide (Na2O)

C. Chlorine gas (Cl2)

D. Sodium hydroxide (NaOH)

Correct Answer: A

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Question 12

A sample of water (H2O) is 10% impure. If 250 mL of this sample is taken, how many moles of pure water are present?

Correct A. 0.0125

B. 0.0127

C. 0.0130

D. 0.0132

Correct Answer: A

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Question 13

A metal (M) reacts with oxygen (O2) to form a basic oxide (MO). If 2.5 g of the metal is heated in air, and 1.5 g of the oxide is formed, what is the percentage yield of the reaction?

A. 60%

Correct B. 70%

C. 80%

D. 90%

Correct Answer: B

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Question 14

A solution of sodium chloride (NaCl) is prepared by dissolving 35 g of the salt in 250 mL of water. What is the concentration of the solution in g/L?

A. 140 g/L

Correct B. 150 g/L

C. 160 g/L

D. 170 g/L

Correct Answer: B

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Question 15

A sample of carbon dioxide (CO2) is collected over water at a temperature of 20°C and a pressure of 1 atm. What is the volume of the gas at STP?

A. 1.5 L

Correct B. 2.0 L

C. 2.5 L

D. 3.0 L

Correct Answer: B

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Question 16

A metal (M) has an atomic radius of 200 pm. If the metal forms a +2 ion, what is the radius of the ion?

Correct A. 100 pm

B. 150 pm

C. 200 pm

D. 250 pm

Correct Answer: A

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Question 17

A solution of hydrochloric acid (HCl) is prepared by dissolving 25 g of the acid in 250 mL of water. What is the concentration of the solution in g/L?

A. 100 g/L

B. 110 g/L

Correct C. 120 g/L

D. 130 g/L

Correct Answer: C

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Question 18

A sample of oxygen (O2) is collected over water at a temperature of 20°C and a pressure of 1 atm. What is the volume of the gas at STP?

A. 2.0 L

Correct B. 2.5 L

C. 3.0 L

D. 3.5 L

Correct Answer: B

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Question 19

A metal (M) has an atomic radius of 250 pm. If the metal forms a +3 ion, what is the radius of the ion?

A. 80 pm

B. 100 pm

Correct C. 120 pm

D. 150 pm

Correct Answer: C

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Question 20

The s\tandard enthalpy of formation of CO2(g) is -393.5 kJ/mol. Calculate the s\tandard enthalpy of formation of CO(g) and O2(g) from their elements in their s\tandard states.

Correct A. ΔH^∘_f(CO(g)) = -110.5 kJ/mol, ΔH^∘_f(O2(g)) = 0 kJ/mol

B. ΔH^∘_f(CO(g)) = -110.5 kJ/mol, ΔH^∘_f(O2(g)) = -248.2 kJ/mol

C. ΔH^∘_f(CO(g)) = -110.5 kJ/mol, ΔH^∘_f(O2(g)) = 248.2 kJ/mol

D. ΔH^∘_f(CO(g)) = 110.5 kJ/mol, ΔH^∘_f(O2(g)) = 248.2 kJ/mol

Correct Answer: A

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Question 21

A 2.50 L flask contains 0.500 mol of an ideal gas at 298 K. Calculate the pressure of the gas u\sing the ideal gas law.

Correct A. P = 1.01 × 10^5 Pa

B. P = 2.01 × 10^5 Pa

C. P = 3.01 × 10^5 Pa

D. P = 4.01 × 10^5 Pa

Correct Answer: A

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Question 22

A 1.00 M solution of NaOH is mixed with a 1.00 M solution of HCl. What is the pH of the resulting solution?

Correct A. pH = 7

B. pH = 8

C. pH = 9

D. pH = 10

Correct Answer: A

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Question 23

A 2.00 g sample of a subs\tance is dissolved in 100.0 mL of water. What is the molarity of the solution?

A. M = 0.100 M

Correct B. M = 0.200 M

C. M = 0.300 M

D. M = 0.400 M

Correct Answer: B

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Question 24

A 1.00 L flask contains 0.500 mol of CO2(g) at 298 K. What is the partial pressure of CO2(g) in the flask?

Correct A. P_{CO_2} = 1.01 × 10^5 Pa

B. P_{CO_2} = 2.01 × 10^5 Pa

C. P_{CO_2} = 3.01 × 10^5 Pa

D. P_{CO_2} = 4.01 × 10^5 Pa

Correct Answer: A

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Question 25

A 2.00 g sample of a subs\tance is burned in a bomb calorimeter. The temperature of the calorimeter increases by 10.0 K. What is the heat of combustion of the subs\tance?

Correct A. \Delta H = -20.0 kJ

B. \Delta H = -30.0 kJ

C. \Delta H = -40.0 kJ

D. \Delta H = -50.0 kJ

Correct Answer: A

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