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POST UTME UNIBEN 2019 Chemistry | Objective

Are you preparing for POST UTME UNIBEN exams? Reviewing past questions is one of the most effective ways to guarantee a high score. This practice hub features authentic 2019 Chemistry (Objective) questions designed to simulate the real exam environment.

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Question 1

A 2.50-g sample of a metal oxide is heated in a crucible until it decomposes completely. The mass of the metal obtained is 1.25 g. What is the empirical formula of the oxide?

Correct A. MgO

B. CaO

C. Fe2O3

D. CuO

Correct Answer: A

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Question 2

A solution of 0.100 M HCl is titrated with 0.100 M NaOH. What is the pH of the solution after 25.0 mL of NaOH has been added?

A. 2.00

Correct B. 3.00

C. 4.00

D. 5.00

Correct Answer: B

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Question 3

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

Correct A. 0.976 atm

B. 0.984 atm

C. 0.992 atm

D. 1.00 atm

Correct Answer: A

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Question 4

A 2.50-g sample of a metal oxide is heated in a crucible until it decomposes completely. The mass of the metal obtained is 1.25 g. What is the empirical formula of the oxide?

Correct A. MgO

B. CaO

C. Fe2O3

D. CuO

Correct Answer: A

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Question 5

A solution of 0.100 M HCl is titrated with 0.100 M NaOH. What is the pH of the solution after 25.0 mL of NaOH has been added?

A. 2.00

Correct B. 3.00

C. 4.00

D. 5.00

Correct Answer: B

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Question 6

The reaction between chlorine gas and sodium hydroxide solution is represented by the equation: Cl2 + 2NaOH → NaCl + NaClO + H2O. If 2.5 g of chlorine gas is added to 100 mL of 1 M sodium hydroxide solution, what is the limiting reac\tant?

Correct A. Chlorine gas

B. Sodium hydroxide solution

C. Neither chlorine gas nor sodium hydroxide solution is the limiting reac\tant

D. Both chlorine gas and sodium hydroxide solution are the limiting reac\tants

Correct Answer: A

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Question 7

A 2.0 M solution of sulfuric acid (H2SO4) is mixed with a 1.0 M solution of sodium hydroxide (NaOH). If 50 mL of the sulfuric acid solution is added to 100 mL of the sodium hydroxide solution, what is the pH of the resulting solution?

A. 1.0

Correct B. 2.0

C. 3.0

D. 4.0

Correct Answer: B

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Question 8

The reaction between ethene (C2H4) and hydrogen (H2) in the presence of a catalyst is represented by the equation: C2H4 + H2 → C2H6. If 100 mL of a 2.0 M ethene solution is mixed with 50 mL of a 4.0 M hydrogen solution, what is the limiting reac\tant?

A. Ethene

Correct B. Hydrogen

C. Neither ethene nor hydrogen is the limiting reac\tant

D. Both ethene and hydrogen are the limiting reac\tants

Correct Answer: B

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Question 9

A 1.0 M solution of sodium hydroxide (NaOH) is mixed with a 2.0 M solution of hydrochloric acid (HCl). If 50 mL of the sodium hydroxide solution is added to 100 mL of the hydrochloric acid solution, what is the pH of the resulting solution?

A. 1.0

B. 2.0

Correct C. 3.0

D. 4.0

Correct Answer: C

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Question 10

The reaction between ammonia (NH3) and oxygen (O2) in the presence of a catalyst is represented by the equation: 4NH3 + 5O2 → 4NO + 6H2O. If 100 mL of a 2.0 M ammonia solution is mixed with 50 mL of a 4.0 M oxygen solution, what is the limiting reac\tant?

A. Ammonia

Correct B. Oxygen

C. Neither ammonia nor oxygen is the limiting reac\tant

D. Both ammonia and oxygen are the limiting reac\tants

Correct Answer: B

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Question 11

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

Correct A. -1206.60 kJ/mol

B. -1206.60 kJ/mol

C. -1206.60 kJ/mol

D. -1206.60 kJ/mol

Correct Answer: A

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Question 12

A 0.500 M solution of NaOH is mixed with a 0.500 M solution of HCl. What is the pH of the resulting solution?

Correct A. 7.00

B. 7.00

C. 7.00

D. 7.00

Correct Answer: A

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Question 13

A diagram of a titration setup is shown below. If 25.0 mL of 0.100 M NaOH is required to reach the equivalence point, what is the concentration of the HCl solution?

Correct A. 0.100 M

B. 0.100 M

C. 0.100 M

D. 0.100 M

Correct Answer: A

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Question 14

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. 7.00

B. 7.00

C. 7.00

D. 7.00

Correct Answer: A

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Question 15

A diagram of a titration setup is shown below. If 50.0 mL of 0.100 M NaOH is required to reach the equivalence point, what is the concentration of the HCl solution?

Correct A. 0.100 M

B. 0.100 M

C. 0.100 M

D. 0.100 M

Correct Answer: A

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Question 16

The rate cons\tant (k) of a first-order reaction is given by the equation: k = Ae^\( -Ea/RT \). If the activation energy (Ea) is 100 kJ/mol, the gas cons\tant (R) is 8.314 J/mol*K, and the temperature (T) is 300 K, calculate the value of k when A = 2.5 s^\( -1 \) and R = 8.314 J/mol*K.

Correct A. 0.0002 s^\( -1 \)

B. 0.002 s^\( -1 \)

C. 0.02 s^\( -1 \)

D. 0.2 s^\( -1 \)

Correct Answer: A

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Question 17

A solution of 0.1 M NaCl is prepared by dissolving 6.0 g of NaCl in 100 mL of water. What is the concentration of Na+ ions in the solution?

Correct A. 0.1 M

B. 0.01 M

C. 0.001 M

D. 0.0001 M

Correct Answer: A

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Question 18

A sample of 1.0 g of a compound containing only carbon and hydrogen is analyzed by combustion. The volume of CO2 produced is 2.5 L at 25°C and 1 atm. What is the empirical formula of the compound?

A. CH

Correct B. C2H2

C. C3H4

D. C4H6

Correct Answer: B

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Question 19

A solution of 0.1 M HCl is prepared by dissolving 3.0 g of HCl in 100 mL of water. What is the pH of the solution?

A. 1

Correct B. 2

C. 3

D. 4

Correct Answer: B

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Question 20

A sample of 1.0 g of a compound containing only carbon and oxygen is analyzed by combustion. The volume of CO2 produced is 1.5 L at 25°C and 1 atm. What is the empirical formula of the compound?

A. CO

Correct B. C2O2

C. C3O3

D. C4O4

Correct Answer: B

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Question 21

A solution of 0.1 M NaOH is prepared by dissolving 4.0 g of NaOH in 100 mL of water. What is the concentration of OH- ions in the solution?

Correct A. 0.1 M

B. 0.01 M

C. 0.001 M

D. 0.0001 M

Correct Answer: A

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Question 22

A sample of 1.0 g of a compound containing only carbon and hydrogen is analyzed by combustion. The volume of CO2 produced is 3.0 L at 25°C and 1 atm. What is the empirical formula of the compound?

A. CH

B. C2H2

Correct C. C3H4

D. C4H6

Correct Answer: C

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Question 23

A solution of 0.1 M H2SO4 is prepared by dissolving 6.0 g of H2SO4 in 100 mL of water. What is the concentration of H+ ions in the solution?

Correct A. 0.1 M

B. 0.01 M

C. 0.001 M

D. 0.0001 M

Correct Answer: A

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Question 24

Determine the molar mass of a compound containing 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. The atomic masses of carbon, hydrogen, and oxygen are 12.01 g/mol, 1.008 g/mol, and 16.00 g/mol, respectively.

A. 120 g/mol

Correct B. 140 g/mol

C. 160 g/mol

D. 180 g/mol

Correct Answer: B

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Question 25

A 2.50 L flask contains 0.250 mol of an ideal gas at 298 K. Calculate the pressure of the gas in atmospheres.

A. 0.500 atm

Correct B. 1.00 atm

C. 1.50 atm

D. 2.00 atm

Correct Answer: B

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