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POST UTME OAU 2023 Chemistry | Objective

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Question 1 View Details

Calculate the s\tandard enthalpy change (ΔH°) for the reaction: 2Al(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2(g). The s\tandard enthalpy of formation (ΔHf°) values are: ΔHf°(AlCl3) = -704.2 kJ/mol, ΔHf°(H2) = 0 kJ/mol, ΔHf°(Al) = 0 kJ/mol, ΔHf°(HCl) = -92.3 kJ/mol.

Correct A. -1668.6 kJ/mol

B. -704.2 kJ/mol

C. -92.3 kJ/mol

D. -1668.6 kJ/mol

Correct Answer: A

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Question 2 View Details

What is the major product of the reaction between 2-methylpropane and chlorine?

A. 1-chloro-2-methylpropane

B. 2-chloro-2-methylpropane

Correct C. 1,1-dichloro-2-methylpropane

D. 1-chloro-1-methylpropane

Correct Answer: C

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Question 3 View Details

A sample of a gas occupies a volume of 2.5 L at a pressure of 1.5 atm. If the temperature is increased to 300 K, what is the new volume of the gas?

A. 3.2 L

Correct B. 4.0 L

C. 5.0 L

D. 6.2 L

Correct Answer: B

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Question 4 View Details

What is the electron configuration of the element with atomic number 18?

A. 1s² 2s² 2p⁶ 3s² 3p⁶

Correct B. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²

C. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹

D. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹

Correct Answer: B

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Question 5 View Details

A solution contains 2.5 g of NaCl in 100 mL of water. What is the molarity of the solution?

Correct A. 0.25 M

B. 0.5 M

C. 1.0 M

D. 2.0 M

Correct Answer: A

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Question 6 View Details

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 View Details

A 2.5 g sample of a non-metallic oxide is heated in a stream of hydrogen gas. If 1.8 g of water is collected, what is the empirical formula of the oxide?

A. MgO

B. CaO

Correct C. SiO2

D. Al2O3

Correct Answer: C

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Question 8 View Details

A 2.5 g sample of a non-metallic oxide is heated in a stream of hydrogen gas. If 1.8 g of water is collected, what is the empirical formula of the oxide?

A. MgO

B. CaO

Correct C. SiO2

D. Al2O3

Correct Answer: C

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Question 9 View Details

A 2.5 g sample of a non-metallic oxide is heated in a stream of hydrogen gas. If 1.8 g of water is collected, what is the empirical formula of the oxide?

A. MgO

B. CaO

Correct C. SiO2

D. Al2O3

Correct Answer: C

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Question 10 View Details

A 2.5 g sample of a non-metallic oxide is heated in a stream of hydrogen gas. If 1.8 g of water is collected, what is the empirical formula of the oxide?

A. MgO

B. CaO

Correct C. SiO2

D. Al2O3

Correct Answer: C

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Question 11 View Details

Determine the number of moles of oxygen gas (O2) produced at STP when 2.5 moles of hydrogen gas (H2) react with oxygen gas according to the equation: 2H2 + O2 → 2H2O.

A. 1.25 moles

B. 2.5 moles

Correct C. 3.75 moles

D. 5 moles

Correct Answer: C

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Question 12 View Details

A 0.5 M solution of sodium hydroxide (NaOH) is mixed with a 0.5 M solution of hydrochloric acid (HCl). What is the pH of the resulting solution?

A. 1

B. 2

Correct C. 7

D. 14

Correct Answer: C

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Question 13 View Details

The diagram below shows a titration setup. If 25 mL of 0.1 M HCl is added to the burette, what is the concentration of the NaOH solution?

A. 0.05 M

Correct B. 0.1 M

C. 0.2 M

D. 0.5 M

Correct Answer: B

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Question 14 View Details

A sample of air contains 20% oxygen, 70% nitrogen, and 10% carbon dioxide. What is the partial pressure of oxygen in the air at a total pressure of 101.3 kPa?

A. 20.26 kPa

B. 20.6 kPa

Correct C. 20.74 kPa

D. 21.0 kPa

Correct Answer: C

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Question 15 View Details

The diagram below shows a simple black and white chemistry apparatus showing titration setup. If 25 mL of 0.1 M HCl is added to the burette, what is the concentration of the NaOH solution?

A. 0.05 M

Correct B. 0.1 M

C. 0.2 M

D. 0.5 M

Correct Answer: B

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Question 16 View Details

The rate cons\tant (k) 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 after 10 minutes?

Correct A. 0.005 M

B. 0.01 M

C. 0.02 M

D. 0.03 M

Correct Answer: A

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Question 17 View Details

A 2.5 g sample of a metal oxide is heated in a crucible until it is completely reduced to its constituent metal. If the mass of the metal obtained is 1.8 g, what is the percentage of the metal in the oxide?

A. 72%

Correct B. 80%

C. 85%

D. 90%

Correct Answer: B

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Question 18 View Details

A solution of 0.1 M NaCl is prepared by dissolving 0.1 g of NaCl in 100 mL of water. What is the concentration of the solution in terms of molality?

Correct A. 0.1 m

B. 0.2 m

C. 0.3 m

D. 0.4 m

Correct Answer: A

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Question 19 View Details

A 10 mL sample of a 0.1 M solution of HCl is titrated with 0.1 M NaOH. What is the pH of the solution after the reaction is complete?

A. 7

Correct B. 8

C. 9

D. 10

Correct Answer: B

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Question 20 View Details

A 2.5 g sample of a metal is heated in a crucible until it is completely oxidized to its oxide. If the mass of the oxide obtained is 3.2 g, what is the percentage of the metal in the oxide?

A. 78%

B. 80%

Correct C. 85%

D. 90%

Correct Answer: C

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Question 21 View Details

The rate cons\tant (k) for 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, what is the value of the pre-exponential factor (A) if the rate cons\tant (k) is 0.05 s^-1?

Correct A. 1.23 x 10^6 s^-1

B. 1.23 x 10^7 s^-1

C. 1.23 x 10^8 s^-1

D. 1.23 x 10^9 s^-1

Correct Answer: A

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Question 22 View Details

A 0.1 M solution of HCl is titrated with 0.1 M NaOH. What is the pH of the solution after 25 mL of NaOH has been added?

A. 1.0

Correct B. 2.0

C. 3.0

D. 4.0

Correct Answer: B

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Question 23 View Details

A metal (M) reacts with oxygen to form a basic oxide. The reaction is: 4M + 3O2 → 2MO3. If 2.5 g of M is heated in air, what is the volume of oxygen required at STP?

A. 1.2 L

Correct B. 1.5 L

C. 2.0 L

D. 2.5 L

Correct Answer: B

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Question 24 View Details

A solution of NaOH is prepared by dissolving 25 g of NaOH in 250 mL of water. What is the concentration of the solution in molarity?

Correct A. 0.1 M

B. 0.2 M

C. 0.3 M

D. 0.4 M

Correct Answer: A

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Question 25 View Details

A 1.0 M solution of HCl is titrated with 1.0 M NaOH. What is the pH of the solution after 50 mL of NaOH has been added?

A. 1.0

Correct B. 2.0

C. 3.0

D. 4.0

Correct Answer: B

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