Chemistry 2013 JAMB Past Questions

1. The presence of an impurity in substance will cause the melting point to

A. be zero
B. reduce
C. increase
D. be stable

Correct Answer: Option B

Explanation

Impurities disrupt the repeating pattern of forces that holds the solid together. So a smaller amount of energy is required to melt the part of the solid surrounding the impurity. If less energy is required, then this explains the melting point depression (lowering) observed from impure solids. The more impure the solid is, the more the structure is disrupted and the greater the variation in intermolecular forces in different areas of the solid.

2. What volume of carbon (ll) oxide is produced by reacting excess carbon with 10 dm³ of oxygen?

A. 5 dm ³
B. 20 dm ³
C. 15 dm ³
D. 10 dm ³

Correct Answer: Option B

3. The rate of diffusion of a gas Y is twice that of Z If the relative molecular mass of Y is 64 and the two gases diffuse under the same conditions, find the relative molecular mass of Z

A. 32
B. 4
C. 8
D. 16

Correct Answer: Option D

Explanation

\sqrt{y}

= 2x

\sqrt{Z}

= x

\frac{r z}{r y}

\sqrt{\frac{m y}{m z}}

\frac{2 x}{x}

\sqrt{\frac{64}{m z}}

\frac{4}{1}

\frac{64}{m z}

mz =

\frac{64}{4}

mz = 16

4. The radioisotope used in industrial radiography for the rapid checking of faults in welds and casting is

A. carbon-14
B. phosphorus-32
C. cobalt-60
D. iodine-131

Correct Answer: Option C

5. The shape of the carbon (lV) oxide molecule is

A. pyramidal
B. linear
C. angular
D. tetrahedral

Correct Answer: Option B

6. Which of the following molecules is held together by hydrogen bond?

A. CH₄
B. HBr
C. H₂SO₄
D. HF

Correct Answer: Option D

7. The bond formed between two elements with electron configurations 1s² 2s² 2p⁶ 3s² and 1s² 2s² 2p⁴ is

A. metallic
B. covalent
C. dative
D. ionic

Correct Answer: Option D

8. The constituent of air that acts as a diluent is

A. nitrogen
B. carbon (IV) oxide
C. noble gases
D. oxygen

Correct Answer: Option A

9. Steam changes the colour of anhydrous cobalt (ll) chloride from

A. white to red
B. blue to white
C. blue to pink
D. white to blue

Correct Answer: Option C

10. An example of a hygroscopic substance is

A. CuO _(S).
B. MgCL_2(S).
C. CaCL_2(S).

Correct Answer: Option A

11. If 24.4 g of lead (ll) trioxonitrate (V) were dissolved in 42 g of distilled water at 20^oC; calculate the solubility of the solute in gdm^-3.

A. 581.000.
B. 0.581
C. 5.810
D. 58.100

Correct Answer: Option A

12. The solvent used for removing grease stain is

A. turpentine
B. ammonia solution
C. ethanol
D. solution of borax in water

Correct Answer: Option B

13. In a water body, too much sewage leads to

A. a decrease in the temperature of the water which cause in death of aquatic animals
B. an increase in the number of aquatic animals in the water
C. an increase in the bacterial population which reduces the level of oxygen in the water
D. a decrease in the bacterial population which increases the level of oxygen in the water

Correct Answer: Option C

14. 10.0 dm³ of water was added to 2.0 mol dm^-3 of 2.5dm³ solution of HCl. What is the concentration of the final solution in mol dm^-3?

A. 0.4
B. 8.0
C. 2.0
D. 0.5

Correct Answer: Option A

Explanation

C₁V₁ = C₂V₂

C₂ =

\frac{C_{1} V_{1}}{V_{2}}

\frac{2.0 \times 2.5}{12.5}

= 0.4mol/dm^-3

15. Three drops of a 1.0 mol dm^-3 solution of HCl was added to 20 cm³ of a solution of pH6.4. The pH of the resulting solution will be

A. close to that of pure water
B. less than 6.4
C. greater than 6.4
D. unaltered

Correct Answer: Option B

16. Which of the following substances is not a salt?

A. Aluminium oxide
B. Sodium hydrogentrioxosulphate (V)
C. Sodium trioxocarbonate (V)
D. Zinc chloride

Correct Answer: Option A

17. An insoluble salt can be prepared by

A. the reaction of trioxocarbonate (V) with an acid
B. double decomposition
C. the action of dilute acid on an insoluble base
D. the reaction of metals with an acid

Correct Answer: Option B

18. 2H₂O _(l) + 2F_2(g) → 4HF_(aq) + O_2(g).

In the reaction above, the substance that is being reduced is

A. O_2(g)
B. H₂O_(l)
C. F₂_(g)
D. HF_(aq)

Correct Answer: Option C

Explanation

F₍₂₎ + 2e

\to

2F^- x 2

2F₂ + 4e

\to

4F^-

19. In an electrochemical cell, polarization is caused by

A. chlorine
B. oxygen
C. tetaoxsulphate (Vl) acid
D. hydrogen

Correct Answer: Option D

20. Calculate the volume in cm3 of oxygen evolved as s.t.p. when a current of 5...

Calculate the volume in cm³ of oxygen evolved as s.t.p. when a current of 5 A is passed through acidified water for 193s
{F = 96500 Cmol^-1, Molar volume of a gas at s.t.p. = 22.4 dm³}

A. 224.000 dm³
B. 0.056 dm³
C. 0.224 dm³
D. 56.000 dm³

Correct Answer: Option B

Explanation

Q = 1 x t

⟹

Q = (5 x 193)C
Q = 965C
40H

⟹

2H₂O + O₂ + 4e

4 X 96500C evolve 22.4 dm³ x 965
4 x 96500 = 0.056 dm³

21. In an endothermic reaction, if there is a loss in entropy the reaction will

A. be indeterminate
B. be spontaneous
C. not be spontaneous
D. be at equilibrium

Correct Answer: Option C

22. the minimum amount of energy required for a reaction to take place is

A. lattice energy
B. ionization energy
C. activation energy
D. kinetic energy

Correct Answer: Option C

23. Which of the following compounds is a neutral oxide?

A. Carbon (IV) oxide
B. Sulphur (Vl) oixide
C. Sulphur (IV) oxide
D. Carbon (ll) oxide

Correct Answer: Option D

24. In the laboratory preparation of ammonia, the flask is placed in a slanting position so as to

A. prevent condensed water from breaking the reaction flask
B. enable the proper mixing of the reactions in the flask
C. enhance the speed of the reaction
D. prevent formation of precipitate

Correct Answer: Option D

25.Which of the gases is employed as an anaesthesia?

A. N ₂O
B. NO₂
C. NH₃
D. NO

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