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POST UTME LASU 2018 Chemistry | Objective

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Question 1

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 of the reac\tant after 10 minutes?

Correct A. 0.01 M

B. 0.05 M

C. 0.1 M

D. 0.2 M

Correct Answer: A

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Question 2

A 2.5 L flask contains 0.5 mol of an ideal gas at 27°C. Calculate the pressure of the gas u\sing the ideal gas law.

A. 1.01 x 10^5 Pa

Correct B. 2.02 x 10^5 Pa

C. 3.03 x 10^5 Pa

D. 4.04 x 10^5 Pa

Correct Answer: B

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Question 3

A solution contains 0.1 M NaCl. If 10 mL of this solution is diluted to 100 mL, what is the concentration of the solution?

Correct A. 0.01 M

B. 0.05 M

C. 0.1 M

D. 0.2 M

Correct Answer: A

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Question 4

A 25 mL sample of a solution containing 0.5 M HCl is titrated with 0.5 M NaOH. What is the pH of the solution after the titration?

A. 7

Correct B. 8

C. 9

D. 10

Correct Answer: B

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Question 5

A metal (X) reacts with oxygen to form a compound (Y). The molar mass of X is 40 g/mol, and the molar mass of Y is 80 g/mol. What is the empirical formula of Y?

Correct A. X2O

B. XO

C. X2O2

D. XO2

Correct Answer: A

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Question 6

Determine the number of moles of electrons transferred during the electrolysis of 2.5 L of 0.5 M H2SO4 solution.

A. 1 mole

Correct B. 2 moles

C. 3 moles

D. 4 moles

Correct Answer: B

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Question 7

Calculate the pH of a solution containing 0.1 M HCl and 0.1 M NaOH.

A. 1

Correct B. 2

C. 3

D. 4

Correct Answer: B

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Question 8

A 2.5 L solution contains 0.5 M H2SO4. Calculate the number of moles of H2SO4.

A. 0.5 moles

Correct B. 1 mole

C. 1.5 moles

D. 2 moles

Correct Answer: B

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Question 9

A 2.5 L solution contains 0.5 M H2SO4. Calculate the number of moles of H2O.

A. 0.5 moles

Correct B. 1 mole

C. 1.5 moles

D. 2 moles

Correct Answer: B

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Question 10

A 2.5 L solution contains 0.5 M H2SO4. Calculate the number of moles of H2O2.

A. 0.5 moles

Correct B. 1 mole

C. 1.5 moles

D. 2 moles

Correct Answer: B

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Question 11

A sample of an ideal gas at 25°C and 1 atm is heated to 100°C at cons\tant pressure. Calculate the change in entropy of the gas.

A. 10 J/K

Correct B. 20 J/K

C. 30 J/K

D. 40 J/K

Correct Answer: B

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Question 12

The reaction 2A(g) + B(g) → 2C(g) has a s\tandard enthalpy change of -200 kJ/mol. If 2.5 mol of A and 1.5 mol of B are mixed, calculate the total enthalpy change.

A. -450 kJ

B. -475 kJ

Correct C. -500 kJ

D. -525 kJ

Correct Answer: C

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Question 13

A 2.0 M solution of NaOH is mixed with a 1.0 M solution of HCl. Calculate 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 14

The compound C2H4O is a primary alcohol. Draw the structure of its enantiomer.

Correct A. CH3CH(OH)CH3

B. CH3CH(OH)CH2CH3

C. CH3CH2CH(OH)CH3

D. CH3CH2CH2CH(OH)CH3

Correct Answer: A

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Question 15

The reaction 2SO2(g) + O2(g) → 2SO3(g) has a s\tandard enthalpy change of -198 kJ/mol. If 2.5 mol of SO2 and 1.5 mol of O2 are mixed, calculate the total enthalpy change.

A. -495 kJ

B. -520 kJ

Correct C. -545 kJ

D. -570 kJ

Correct Answer: C

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Question 16

Calculate the s\tandard enthalpy of formation of NH3(g) from the following data: ΔHf(NH3(g)) = ?; ΔHf(H2(g)) = -285.8 kJ/mol; ΔHf(N2(g)) = 0 kJ/mol.

A. -46.1 kJ/mol

B. -92.2 kJ/mol

Correct C. -46.1 kJ/mol

D. -92.2 kJ/mol

Correct Answer: C

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Question 17

A 2.5 M solution of HCl is mixed with a 1.5 M solution of NaOH. Calculate the concentration of the resulting solution after the reaction is complete.

A. 1.5 M

B. 2.5 M

Correct C. 3.0 M

D. 4.0 M

Correct Answer: C

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Question 18

The half-life of a radioactive subs\tance is 5 years. If 100 g of the subs\tance is present initially, how much will be left after 15 years?

A. 25 g

Correct B. 50 g

C. 75 g

D. 100 g

Correct Answer: B

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Question 19

A sample of CO2 gas occupies a volume of 2.5 L at a pressure of 1.5 atm. What is the volume of the gas at a pressure of 3.0 atm, assuming the temperature remains cons\tant?

A. 1.0 L

Correct B. 1.5 L

C. 2.0 L

D. 2.5 L

Correct Answer: B

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Question 20

A 10.0 g sample of a metal oxide is heated in a crucible until it decomposes completely. If 5.0 g of the metal is obtained, what is the empirical formula of the oxide?

A. MgO

B. CaO

Correct C. Fe2O3

D. CuO

Correct Answer: C

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Question 21

The molecular formula for a hydrocarbon is C4H10. What is the name of the compound?

A. Bu\tane

B. Isobu\tane

Correct C. n-Bu\tane

D. Isopen\tane

Correct Answer: C

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Question 22

A solution contains 10 g of NaCl in 100 g of water. What is the molality of the solution?

A. 0.1 m

B. 0.5 m

Correct C. 1.0 m

D. 5.0 m

Correct Answer: C

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Question 23

The diagram below shows the structure of a compound. What is the name of the compound?

A. Ethanol

B. Propanol

Correct C. Bu\tanol

D. Pen\tanol

Correct Answer: C

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Question 24

The half-life of a radioactive subs\tance is 10 years. If the initial amount of the subs\tance is 100 g, what is the amount remaining after 20 years?

A. 50 g

B. 25 g

Correct C. 12.5 g

D. 6.25 g

Correct Answer: C

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Question 25

A solution contains 5 g of glu\cose in 100 g of water. What is the molarity of the solution?

A. 0.1 M

B. 0.5 M

Correct C. 1.0 M

D. 5.0 M

Correct Answer: C

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