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POST UTME NOUN 2022 Chemistry | Objective

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Question 1 View Details

The rate cons\tant (k) of a first-order reaction is related to the half-life \( t_\( 1/2 \ \)) by the equation: \( k = \frac{ln{2}}{t_{1/2}} \). If the half-life of a reaction is 20 minutes, what is the value of k?

Correct A. 0.0347 min^\( -1 \)

B. 0.0357 min^\( -1 \)

C. 0.0367 min^\( -1 \)

D. 0.0377 min^\( -1 \)

Correct Answer: A

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Question 2 View Details

A 2.50-g sample of a compound containing only carbon and hydrogen is analyzed by combustion. The amount of CO_(2) produced is 1.25 g, and the amount of H_(2)O produced is 0.75 g. What is the empirical formula of the compound?

A. CH_(2)

Correct B. C_(2)H_(4)

C. C_(3)H_(6)

D. C_(4)H_(8)

Correct Answer: B

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Question 3 View Details

A solution contains 5.00 g of NaCl in 250.0 mL of water. What is the molarity of the solution?

A. 0.20 M

Correct B. 0.25 M

C. 0.30 M

D. 0.35 M

Correct Answer: B

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Question 4 View Details

A 1.00-L sample of a gas at 25°C and 1.00 atm is compressed to 2.00 atm at cons\tant temperature. What is the new volume of the gas?

A. 0.50 L

B. 0.75 L

Correct C. 1.00 L

D. 1.25 L

Correct Answer: C

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Question 5 View Details

A 2.00-g sample of a metal is dissolved in 10.0 mL of acid. The resulting solution is then titrated with 0.100 M NaOH. If 25.0 mL of NaOH is required to reach the equivalence point, what is the molar mass of the metal?

A. 50.0 g/mol

B. 60.0 g/mol

Correct C. 70.0 g/mol

D. 80.0 g/mol

Correct Answer: C

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Question 6 View Details

The reaction of magnesium with hydrochloric acid produces magnesium chloride and hydrogen gas. Write the balanced chemical equation for this reaction, including the state of each subs\tance.

A. \text{Mg}(s) + \text{HCl}(aq) \rightarrow \text{MgCl}(aq) + \text{H}_2(g)

Correct B. \text{Mg}(s) + 2\text{HCl}(aq) \rightarrow \text{MgCl}_2(aq) + \text{H}_2(g)

C. \text{Mg}(s) + \text{HCl}(aq) \rightarrow \text{MgCl}_2(aq) + \text{H}_2(g)

D. \text{Mg}(s) + 2\text{HCl}(aq) \rightarrow \text{MgCl}(aq) + \text{H}_2(g)

Correct Answer: B

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Question 7 View Details

The half-life of a radioactive subs\tance is 5 years. If a sample of this subs\tance has an initial activity of 100 Bq, what is its activity after 10 years?

Correct A. 12.5 Bq

B. 25 Bq

C. 50 Bq

D. 100 Bq

Correct Answer: A

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Question 8 View Details

A solution contains 0.1 M NaOH and 0.2 M HCl. What is the pH of the resulting solution?

A. 1

Correct B. 2

C. 3

D. 4

Correct Answer: B

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Question 9 View Details

The reaction of sodium with water produces sodium hydroxide and hydrogen gas. Write the balanced chemical equation for this reaction, including the state of each subs\tance.

Correct A. \text{Na}(s) + \text{H}_2\text{O}(l) \rightarrow \text{NaOH}(aq) + \text{H}_2(g)

B. \text{Na}(s) + 2\text{H}_2\text{O}(l) \rightarrow \text{NaOH}(aq) + \text{H}_2(g)

C. \text{Na}(s) + \text{H}_2\text{O}(l) \rightarrow \text{NaO}(aq) + \text{H}_2(g)

D. \text{Na}(s) + 2\text{H}_2\text{O}(l) \rightarrow \text{NaO}(aq) + \text{H}_2(g)

Correct Answer: A

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Question 10 View Details

A solution contains 0.1 M HCl and 0.2 M NaOH. What is the pH of the resulting solution?

A. 1

Correct B. 2

C. 3

D. 4

Correct Answer: B

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Question 11 View Details

The rate cons\tant (k) of a first-order reaction is given by the equation: ln\( [A]t/[A]0 \) = -kt. If the half-life of the reaction is 10 minutes, what is the value of k?

Correct A. 0.0693 min^-1

B. 0.0693 min^-1

C. 0.693 min^-1

D. 0.693 min^-1

Correct Answer: A

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Question 12 View Details

A solution contains 0.1 M NaOH and 0.1 M HCl. What is the pH of the solution after mixing?

Correct A. 0

B. 1

C. 7

D. 14

Correct Answer: A

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Question 13 View Details

A gas occupies a volume of 2.5 L at a pressure of 1.5 atm. What is the pressure of the gas if the volume is reduced to 1.2 L?

A. 2.5 atm

B. 3.0 atm

Correct C. 3.5 atm

D. 4.0 atm

Correct Answer: C

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Question 14 View Details

A solution contains 0.1 M NaOH and 0.1 M HCl. What is the concentration of OH^- ions in the solution after mixing?

A. 0.1 M

Correct B. 0.2 M

C. 0.3 M

D. 0.4 M

Correct Answer: B

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Question 15 View Details

A gas occupies a volume of 2.5 L at a pressure of 1.5 atm. What is the volume of the gas if the pressure is increased to 3.0 atm?

A. 1.5 L

B. 2.0 L

Correct C. 2.5 L

D. 3.0 L

Correct Answer: C

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Question 16 View Details

Determine the rate cons\tant (k) for the reaction: 2NO(g) → N2(g) + O2(g) at 298 K, given that the initial concentration of NO is 0.1 M and the half-life of the reaction is 10 minutes.

A. \( 2.303 \times 10^{-3} , \text{min}^{-1} \)

Correct B. \( 4.606 \times 10^{-3} , \text{min}^{-1} \)

C. \( 6.909 \times 10^{-3} , \text{min}^{-1} \)

D. \( 9.212 \times 10^{-3} , \text{min}^{-1} \)

Correct Answer: B

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Question 17 View Details

A 25 mL sample of 0.1 M HCl is titrated with 0.1 M NaOH. Calculate the pH of the solution after 20 mL of NaOH has been added.

A. ( 2.303 )

B. ( 4.605 )

Correct C. ( 6.907 )

D. ( 9.209 )

Correct Answer: C

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Question 18 View Details

The s\tandard electrode potential for the cell: Zn(s) | Zn²⁺(aq) || Cu²⁺(aq) | Cu(s) is 1.10 V. Calculate the emf of the cell when the concentration of Zn²⁺ is 0.1 M and the concentration of Cu²⁺ is 0.01 M.

A. \( 1.10 , \text{V} \)

B. \( 1.20 , \text{V} \)

Correct C. \( 1.30 , \text{V} \)

D. \( 1.40 , \text{V} \)

Correct Answer: C

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Question 19 View Details

A 2.0 g sample of a metal oxide is heated in a crucible until it decomposes completely. The mass of the metal obtained is 1.2 g. Calculate the mass of oxygen in the original sample.

Correct A. \( 0.8 , \text{g} \)

B. \( 1.0 , \text{g} \)

C. \( 1.2 , \text{g} \)

D. \( 1.4 , \text{g} \)

Correct Answer: A

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Question 20 View Details

A 100 mL sample of a solution containing 0.1 M NaOH is titrated with 0.1 M HCl. Calculate the volume of HCl required to reach the equivalence point.

A. \( 50 , \text{mL} \)

B. \( 75 , \text{mL} \)

Correct C. \( 100 , \text{mL} \)

D. \( 125 , \text{mL} \)

Correct Answer: C

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Question 21 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 22 View Details

A metal (X) reacts with hydrochloric acid to produce hydrogen gas. The reaction is as follows: X + 2HCl → XCl2 + H2. If 2.5 g of X reacts with 2.5 g of HCl, what is the molar mass of X?

A. 40

Correct B. 80

C. 120

D. 160

Correct Answer: B

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Question 23 View Details

A solution of sodium hydroxide (NaOH) is titrated with a solution of hydrochloric acid (HCl). The initial pH of the NaOH solution is 12. If 25 mL of 0.1 M HCl is added to 25 mL of 0.1 M NaOH, what is the pH of the resulting solution?

A. 7

Correct B. 8

C. 9

D. 10

Correct Answer: B

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Question 24 View Details

A sample of a polymer (X) has a molecular weight of 5000 g/mol. If 1 g of X is dissolved in 100 mL of water, what is the concentration of the solution in g/L?

A. 50

Correct B. 100

C. 150

D. 200

Correct Answer: B

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Question 25 View Details

A compound (X) has the molecular formula C6H12O6. If 1 mole of X is burned in oxygen, what is the volume of carbon dioxide gas produced at STP?

A. 22.4

Correct B. 44.8

C. 67.2

D. 89.6

Correct Answer: B

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