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POST UTME UNIPORT 2021 Chemistry | Objective

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Question 1

Determine the s\tandard electrode potential of the cell represented by the following reaction: MnO4- + 8H+ + 5e- → Mn2+ + 4H2O. Given that the s\tandard electrode potential of MnO4-/Mn2+ is +1.23 V.

Correct A. +1.23 V

B. -1.23 V

C. +1.48 V

D. +2.23 V

Correct Answer: A

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Question 2

A 0.1 M solution of K2Cr2O7 is titrated with a 0.1 M solution of FeSO4. The reaction is: Cr2O72- + 14H+ + 6Fe2+ → 2Cr3+ + 7H2O + 6Fe3+. Calculate the number of moles of Fe2+ required to react with 50 mL of the K2Cr2O7 solution.

A. 0.0025 mol

Correct B. 0.005 mol

C. 0.0075 mol

D. 0.01 mol

Correct Answer: B

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Question 3

A diagram of a titration setup is shown below. The diagram shows a burette containing a 0.1 M solution of HCl and a flask containing a 0.1 M solution of NaOH. The reaction is: HCl + NaOH → NaCl + H2O. If 25 mL of the HCl solution is added to the flask, what is the resulting pH of the solution?

A. 1

B. 2

C. 3

Correct D. 4

Correct Answer: D

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Question 4

A 0.1 M solution of CH3COOH is titrated with a 0.1 M solution of NaOH. The reaction is: CH3COOH + NaOH → CH3COONa + H2O. Calculate the number of moles of NaOH required to react with 50 mL of the CH3COOH solution.

A. 0.0025 mol

Correct B. 0.005 mol

C. 0.0075 mol

D. 0.01 mol

Correct Answer: B

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Question 5

A diagram of a chromatography setup is shown below. The diagram shows a column containing a mixture of CH3CH2CH3 and CH3CH2CH2CH3. The reaction is: CH3CH2CH3 + CH3CH2CH2CH3 → CH3CH2CH2CH2CH3 + CH3CH2CH3. If the mixture is separated u\sing chromatography, what is the resulting composition of the mixture?

A. CH3CH2CH3: 50%, CH3CH2CH2CH3: 50%

Correct B. CH3CH2CH3: 75%, CH3CH2CH2CH3: 25%

C. CH3CH2CH3: 25%, CH3CH2CH2CH3: 75%

D. CH3CH2CH3: 100%, CH3CH2CH2CH3: 0%

Correct Answer: B

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Question 6

A solution of $NH_4Cl$ is prepared by dissolving $NH_4Cl(s)$ in water. The resulting solution is found to be 0.15 M in $NH_4^+$ ions. What is the concentration of $Cl^-$ ions in the solution?

A. 0.15 M

Correct B. 0.30 M

C. 0.45 M

D. 0.60 M

Correct Answer: B

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Question 7

A sample of $CaCO_3$ is heated in a crucible until it decomposes completely. The mass of the crucible and its contents before heating is 50.0 g, and the mass after heating is 45.0 g. What is the mass of $CO_2$ produced during the decomposition?

A. 2.00 g

B. 4.00 g

Correct C. 6.00 g

D. 8.00 g

Correct Answer: C

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Question 8

A 2.50 L sample of a gas at 27°C and 1.00 atm is collected over water at 27°C. The vapor pressure of water at 27°C is 0.0313 atm. What is the partial pressure of the gas?

Correct A. 0.969 atm

B. 0.980 atm

C. 0.991 atm

D. 1.00 atm

Correct Answer: A

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Question 9

A solution of $H_2SO_4$ is prepared by dissolving $H_2SO_4(s)$ in water. The resulting solution is found to be 0.25 M in $H_2SO_4$. What is the concentration of $H^+$ ions in the solution?

Correct A. 0.25 M

B. 0.50 M

C. 0.75 M

D. 1.00 M

Correct Answer: A

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Question 10

A sample of $NaCl$ is dissolved in water to form a solution. The resulting solution is found to be 0.10 M in $Na^+$ ions. What is the concentration of $Cl^-$ ions in the solution?

Correct A. 0.10 M

B. 0.20 M

C. 0.30 M

D. 0.40 M

Correct Answer: A

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Question 11

Determine the pH of a 0.1 M solution of HCl at 25°C. The dissociation cons\tant of HCl is 10^$ -7 $.

A. 1

B. 2

C. 3

Correct D. 4

Correct Answer: D

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Question 12

A 25 mL sample of 0.1 M HCl is titrated with 0.1 M NaOH. Calculate the pH after the addition of 10 mL of NaOH.

A. 2

B. 3

C. 4

Correct D. 5

Correct Answer: D

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Question 13

The rate cons\tant of a first-order reaction is 0.05 min^$ -1 $. If the initial concentration of the reac\tant is 0.1 M, calculate the concentration after 10 minutes.

A. 0.05

B. 0.1

Correct C. 0.2

D. 0.3

Correct Answer: C

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Question 14

A polymer has a molecular weight of 100,000 g/mol and a degree of polymerization of 500. Calculate the molar mass of the repeating unit.

A. 100

B. 200

Correct C. 300

D. 400

Correct Answer: C

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Question 15

The atomic radius of an element is 100 pm. If the element has an atomic number of 20, calculate the number of electrons in a \single atom.

A. 18

Correct B. 20

C. 22

D. 24

Correct Answer: B

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Question 16

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, ΔHf(C(s)) = 0 kJ/mol.

Correct A. -1206.60 kJ/mol

B. -1206.19 kJ/mol

C. -1206.91 kJ/mol

D. -1207.01 kJ/mol

Correct Answer: A

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Question 17

A 2.50-g sample of a non-metallic element, X, reacts with oxygen to form 3.25 g of X2O5. Calculate the empirical formula of X.

Correct A. X2O5

B. XO2

C. XO3

D. XO4

Correct Answer: A

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Question 18

A 25.0-mL sample of 0.100 M HCl is titrated with 0.100 M NaOH. Calculate the number of moles of HCl that react with NaOH.

A. 0.0025 mol

Correct B. 0.0050 mol

C. 0.0075 mol

D. 0.0100 mol

Correct Answer: B

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Question 19

A metal, M, has an atomic radius of 0.200 nm and an electron affinity of -3.00 eV. Calculate the ionization energy of M.

Correct A. -3.00 eV

B. -2.00 eV

C. -1.00 eV

D. 0.00 eV

Correct Answer: A

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Question 20

A 1.00-g sample of a metal, M, is heated in a Bunsen burner flame. The resulting oxide has a mass of 1.25 g. Calculate the percentage of M that is converted to oxide.

A. 25.0%

Correct B. 30.0%

C. 35.0%

D. 40.0%

Correct Answer: B

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Question 21

At 25°C, the s\tandard enthalpy of formation of CO2(g) is -393.5 kJ/mol. If 2.5 mol of CO2(g) is produced at cons\tant pressure, what is the change in enthalpy?

Correct A. -987.5 kJ

B. -984.5 kJ

C. -987.0 kJ

D. -984.0 kJ

Correct Answer: A

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Question 22

A 0.5 M solution of HCl is titrated with a 0.5 M solution of NaOH. If 25 mL of NaOH is required to reach the equivalence point, what is the volume of HCl used?

A. 25 mL

Correct B. 50 mL

C. 12.5 mL

D. 62.5 mL

Correct Answer: B

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Question 23

A metal (M) reacts with oxygen to form a basic oxide. The reaction is as follows: 4M + 3O2 → 2MO3. If 3.2 g of M is heated in air, what is the volume of O2 consumed at STP?

A. 2.4 L

B. 2.8 L

Correct C. 3.2 L

D. 1.6 L

Correct Answer: C

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Question 24

A 1.0 M solution of CH3OH is titrated with a 1.0 M solution of HCl. If 20 mL of HCl is required to reach the equivalence point, what is the volume of CH3OH used?

A. 20 mL

Correct B. 40 mL

C. 10 mL

D. 80 mL

Correct Answer: B

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Question 25

A metal (M) reacts with oxygen to form a basic oxide. The reaction is as follows: 4M + 3O2 → 2MO3. If 3.2 g of M is heated in air, what is the mass of MO3 formed?

A. 6.4 g

B. 8.0 g

Correct C. 9.6 g

D. 12.8 g

Correct Answer: C

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