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POST UTME EKSU 2020 Chemistry | Objective

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Question 1

Determine the mass of copper (Cu) required to produce 2.5 kg of copper oxide (CuO) u\sing the reaction: Cu + O2 → CuO. The molar mass of Cu is 63.5 g/mol, and the molar mass of O2 is 32 g/mol.

A. 0.5 kg

B. 1.0 kg

Correct C. 1.25 kg

D. 2.0 kg

Correct Answer: C

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Question 2

A 2.5 M solution of HCl is titrated with 0.1 M NaOH. Calculate the volume of NaOH required to reach the equivalence point.

A. 25 mL

B. 50 mL

Correct C. 75 mL

D. 100 mL

Correct Answer: C

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Question 3

The diagram below shows a titration setup. Identify the part labeled A.

Correct A. Burette

B. Beaker

C. Conical Flask

D. Erlenmeyer Flask

Correct Answer: A

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Question 4

A sample of nitrogen gas (N2) occupies a volume of 2.5 L at a pressure of 1 atm and a temperature of 298 K. Calculate the number of moles of N2 present.

A. 0.1 mol

Correct B. 0.2 mol

C. 0.3 mol

D. 0.4 mol

Correct Answer: B

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Question 5

The diagram below shows a periodic table. Identify the element with atomic number 6.

Correct A. Carbon

B. Nitrogen

C. Oxygen

D. Fluorine

Correct Answer: A

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Question 6

The energy change associated with the formation of a mole of liquid water from its gaseous state at 298 K is -44.0 kJ/mol. What is the s\tandard enthalpy of vaporization of water at this temperature?

Correct A. -44.0 kJ/mol

B. -44.0 kJ/g

C. 44.0 kJ/mol

D. 44.0 kJ/g

Correct Answer: A

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Question 7

A 0.500 M solution of NaCl is prepared by dissolving 25.0 g of NaCl in enough water to make 1.00 L of solution. What is the concentration of Cl^- ions in the solution?

A. 0.250 M

Correct B. 0.500 M

C. 0.750 M

D. 1.00 M

Correct Answer: B

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Question 8

A sample of a gas occupies 2.50 L at 25.0°C and 1.00 atm. What is the volume of the gas at 50.0°C and 2.00 atm?

A. 3.00 L

B. 3.50 L

Correct C. 4.00 L

D. 4.50 L

Correct Answer: C

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Question 9

A 2.00 M solution of HCl is prepared by dissolving 40.0 g of HCl in enough water to make 1.00 L of solution. What is the concentration of H^+ ions in the solution?

A. 1.00 M

Correct B. 2.00 M

C. 4.00 M

D. 8.00 M

Correct Answer: B

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Question 10

A sample of a gas occupies 1.50 L at 20.0°C and 0.500 atm. What is the volume of the gas at 30.0°C and 1.00 atm?

A. 1.75 L

Correct B. 2.00 L

C. 2.25 L

D. 2.50 L

Correct Answer: B

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Question 11

Determine the pH of a 0.1 M solution of HCl at 25°C.

A. 1

B. 2

C. 3

Correct D. 4

Correct Answer: D

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Question 12

A 25 mL sample of 0.5 M H2SO4 is titrated with 0.5 M NaOH. Calculate the number of moles of H2SO4.

A. 0.1

Correct B. 0.2

C. 0.3

D. 0.4

Correct Answer: B

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Question 13

The s\tandard enthalpy of formation of CO2(g) is -393.5 kJ/mol. Calculate the s\tandard enthalpy of formation of CH4(g) if the s\tandard enthalpy of formation of C(s) is -394.4 kJ/mol and the s\tandard enthalpy of formation of H2(g) is 0 kJ/mol.

A. -74.8

B. -74.9

Correct C. -75.0

D. -75.1

Correct Answer: C

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Question 14

A 1.0 L sample of a solution containing 0.1 M NaCl is mixed with 1.0 L of a solution containing 0.2 M NaOH. Calculate the concentration of the resulting solution.

A. 0.05

B. 0.1

Correct C. 0.15

D. 0.2

Correct Answer: C

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Question 15

A 50 mL sample of a solution containing 0.5 M HCl is titrated with 0.5 M NaOH. Calculate the pH of the resulting solution.

A. 1

B. 2

C. 3

Correct D. 4

Correct Answer: D

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Question 16

Determine the rate cons\tant (k) for the first-order reaction: A → B, given that the initial concentration of A is 0.1 M and the concentration of A after 2 minutes is 0.05 M. The rate cons\tant is related to the half-life \( t1/2 \) by the equation: k = ln(2) / t1/2.

Correct A. 0.693 min^-1

B. 1.386 min^-1

C. 0.693 min^-2

D. 1.386 min^-2

Correct Answer: A

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Question 17

A sample of nitrogen gas (N2) at 25°C and 1 atm is heated to 50°C. Calculate the new volume of the gas, assuming the temperature change is isothermal.

A. 2.00 L

Correct B. 2.50 L

C. 3.00 L

D. 3.50 L

Correct Answer: B

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Question 18

A solution of 0.1 M NaCl is electrolyzed u\sing a platinum electrode. Calculate the mass of chlorine gas (Cl2) produced at the anode after 2 hours, assuming a current of 1 A and a cell potential of 2.0 V.

A. 0.50 g

Correct B. 1.00 g

C. 1.50 g

D. 2.00 g

Correct Answer: B

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Question 19

A sample of sulfur (S8) is heated in a stream of oxygen gas (O2) to produce sulfur trioxide (SO3). Calculate the number of moles of SO3 produced from 1.00 g of S8, assuming a 100% yield.

A. 0.25 mol

Correct B. 0.50 mol

C. 0.75 mol

D. 1.00 mol

Correct Answer: B

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Question 20

A polymer sample is analyzed u\sing gel permeation chromatography (GPC). The chromatogram shows a peak at 10 minutes with a retention volume of 20 mL. Calculate the molecular weight of the polymer, assuming a calibration curve with a slope of 1.00 mL/min.

A. 10^4 g/mol

B. 10^5 g/mol

Correct C. 10^6 g/mol

D. 10^7 g/mol

Correct Answer: C

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Question 21

Determine the s\tandard potential of the cell represented by the following reaction: Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s). Given that the s\tandard reduction potential of Cu2+/Cu is +0.34 V and that of Zn2+/Zn is -0.76 V.

Correct A. +0.58 V

B. +0.52 V

C. +0.68 V

D. +0.48 V

Correct Answer: A

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Question 22

A 25.0 mL sample of 0.100 M HCl is added to 50.0 mL of 0.0500 M NaOH. Calculate the number of moles of HCl that react with NaOH.

Correct A. 0.00250 mol

B. 0.00300 mol

C. 0.00200 mol

D. 0.00150 mol

Correct Answer: A

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Question 23

The half-life of a radioactive subs\tance is 5.00 days. If 100.0 mg of the subs\tance is initially present, how much will remain after 20.0 days?

Correct A. 12.5 mg

B. 25.0 mg

C. 50.0 mg

D. 100.0 mg

Correct Answer: A

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Question 24

A solution contains 0.100 M NaCl. What is the concentration of Cl- ions in the solution?

A. 0.0500 M

Correct B. 0.100 M

C. 0.150 M

D. 0.200 M

Correct Answer: B

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Question 25

A 2.00 L flask contains 0.500 M H2(g) at 25.0°C. What is the partial pressure of H2(g) in the flask?

A. 0.500 atm

Correct B. 1.00 atm

C. 1.50 atm

D. 2.00 atm

Correct Answer: B

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