Chemistry 2012 JAMB Past Questions

1. Which of the following methods can be used to obtain pure water from a mixture of sand, water and methanoic acid?

A. netralization with NaOHfoolowed by filtration
B. neutralization with NaOH followed by distillation
C. fractional distillation
D. filtration followed by distillation

Correct Answer: Option D

2. How many atoms are present in 6.0g of magnesium?

[Mg = 24, N_A = 6.02 x 10²³ mol^-1]

A. 1.20 x 10²²
B. 2.41 x 10²²
C. 1.51 x 10²³
D. 3.02 x 10²³

Correct Answer: Option C

3. 50 cm³ of gas was collected over water at 10^oC and 765 mm Hg. Calculate the volume of the gas at s.t.p. if the saturated vapour pressure of water at 10 ^oC is 5mm Hg

A. 49.19 cm ³
B. 48.87 cm ³
C. 48.55 cm ³
D. 48.23 cm ³

Correct Answer: Option D

4. An increase in the pressure exerted on gas at a constant temperature results in

A. a decrease in the number of effective collisions
B. a decrease in volume
C. an increase in the average intermolecular distance
D. an increase in volume

Correct Answer: Option B

5. 2H_2(g) + O_2(g) → 2H₂ O_(g)

In the reaction above, what volume of hydrogen would be left over when 300 cm³ of oxygen and 1000 cm³ of hydrogen are exploded in a sealed tube?

A. 200 cm³
B. 400 cm³
C. 600 cm³

Correct Answer: Option B

l . Evaporation. ll. Sublimation. lll. Diffusion. IV. Brownian motion.
Which of the above can correctly be listed as evidences for the particulate nature of matter?

A. I and lll only
B. ll and lV only
C. l, ll and lll only
D. l, ll, lll and lV

Correct Answer: Option D

7. If the elements X and Y have atomic numbers 11 and 17 respectively, what type of bond can they form?

A. Dative
B. Covalent
C. Lonic
D. Metallic

Correct Answer: Option C

8. A hydrogen atom which has lost an electron contains

A. one proton only
B. one neutron only
C. one proton and one neutron
D. one proton, one electron and one neutron

Correct Answer: Option C

9. The electronic configuration of Mg ²⁺ is

A. ls ²2s ²2P ⁶3s²3P²
B. Is²2s²2P⁶
C. ls²2s²2p⁶3s²
D. ls²2s²2P⁴

Correct Answer: Option B

10. Group VII elements are

A. monoatmic
B. good oxidizing agents
C. highly electropositive
D. electron donors

Correct Answer: Option B

11. Which of the following is used to study the arrangement of particles in crystal lattices?

A. Alpha-particles
B. Beta-particles
C. Gamma-rays
D. X-rays

Correct Answer: Option D

I. It has a varied composition from one place to another. ll. it constituents can be separated by physical means
lll. It contains unreactive noble gases
which of the above shows that air is a mixture?

A. I and ll only
B. ll and lll only
C. l and lll only
D. l,lll and lll

Correct Answer: Option A

13. The chemicals used to soften hard water involves the addition of

A. insoluble sodium compounds which from soluble solutions of calcium and magesium
B. solube soudium compounds which from soluble solutions of calcium and magnesium ions
C. solube sodium compounds which from insoluble precipitates of calcium and magnesium ions
D. insoluble precipitates of calcium and magnesium ions

Correct Answer: Option C

14. Chlorination of water for town supply is carried out to

A. make the water colourless
B. remove germs from the water
C. make the water tastedful
D. remove odour from the water

Correct Answer: Option B

15. The solubilites of different solutes in a given solvent can be compared by

A. plotting their solubility curves on separete axes
B. plotting their solubility curves on the same axes
C. plotting some of the solubility curves on the x-axis and others on the y-axis
D. plotting their solubility curves on the x-axis only

Correct Answer: Option B

16. Potassium trioxochlorate (V)has a solubility of 1.5 mol dm ^-3 at 45 ^oC.On cooling this solution to a temperature of 20 ^oC, the solubility was found to be 0.5 mol dm ^-3. What mass of KCIO ₃ was crystalized out?

[K = 39, Cl = 35.5 O =16]

A. 1.00g
B. 10.00g
C. 12.25g
D. 122.50g

Correct Answer: Option D

17. Which of the following pollutants is associated with brain damage?

A. Carbon (ll) oxide
B. Radioactive fallout
C. Biodegradable waste
D. Sulphus (lV) oxide

Correct Answer: Option B

18. Which of the following will produce a solution with pH less than 7 at equivalent point?

A. HNO ₃ +NaOH
B. H ₂SO ₄ + KOH
C. HC +Mg (OH) ₂
D. HNO ₃ + KOH

Correct Answer: Option C

19. The number of hydroxonium ions produced by one molecule of an acid in aqueous solution is its

A. basicity
B. acid strength
C. pH
D. concentration

Correct Answer: Option A

Explanation

The basicity of an acid is the number of replaceable Hydrogen ions,

H^{+}

, or Hydroxonium ion,

H_{3} O^{+}

in one molecule of the acid.

20. During a titration experiment, 0.05 moles of carbon (lV) oxide is liberated. What is the volume of gas liberated?

A. 22.40 dm ³
B. 11.20 dm ³
C. 2.24 dm ³
D. 1.12 dm ³
Correct Answer: Option D
21. A major factor considered in selecting a suitable method for preparing a simple salt is its
- A. Crystalline from
- B. melting point
- C. reactivity with dilute acids
- D. solubility in water
Correct Answer: Option D

22. The oxidation number of boron in NaBH ₄ is
- A. -3
- B. -1
- C. +1
- D. +3
Correct Answer: Option D
23. 2Na ₂ O _2(s) + 2H ₂ O ₂₍₁₎ → 4 NaOH_(s) +O_2(s)
The substance that is oxidized in the reaction above is
- A. 2NaO_2(s)
- B. NaOH(aq)
- C. H₂O₍₁₎
- D. O_2(g)
Correct Answer: Option A

24. What number of moles of Cu 2+ will be deposited by 360 coulombs of electricity?
[f = 96500 C mol -1]
- A. 5.36 x 10 ^-4 mole
- B. 1. 87 x 10 10 ^-3 mole
- C. 9. 35 x 10 ^-4 mole
- D. 3. 73 x 10 ^-3
Correct Answer: Option B

Explanation
Cu $^{2 +}$
+ 2e $^{-}$ $_{(a q)}$ $\to$ Cu $_{(s)}$ Liberating 1 mole of Cu
2 x 1F = 2 x 96,500C = 193,000C of electricity is needed
Hence, 193,000C = 1 mole
360C of electricity = $\frac{360 C \times 1 m o l}{193, 000 C}$
= 0.001865 mol
= 1.87 x 10 $^{- 3}$
moles

25. A metal M displaces zinc from ZnCl, solution, solution

This shows that
A. electrons flow from zinc to M
B. M is more electropositive than zinc
C. M is more electonegative than zinc
D. zinc is more electropositive than M

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