WAEC Chemistry Past Questions & Answers

916.

What are the values of x, y and z respectively in the following in the following equation? $MnO_{2(s)} + xHCI_{(aq)} → MnCI_{2(g)} + yHO_{(l)} + zCI_{2(g)}$

4,1,2

1,2,1

2,1,2

4,2,1

View answer & explanation

Correct answer is D

$MnO_{2(s)} + xHCI_{(aq)} → MnCI_{2(g)} + yH_2O_{(l)} + zCI_{2(g)}$

compare the number of each atom of the elements on both sides of the chemical equation.

x = 4, y = 2 and z = 1

917.

What volume of hydrogen would be left over when 300cm³ of oxygen and 1000cm of hydrogen are exploded in a sealed tube? [2H_2(g) + O_2(g) → 2H₂ O_g]

200 cm³

400 cm³

600cm³

700cm³

View answer & explanation

Correct answer is B

2H_2(g) + O _2(g) → 2H₂O_g
2V IV 2V
600cm³ 300cm³ 600cm³
The volume of hydrogen left over
= 1000 - 600 = 400cm³?

918.

Which of the following salts is not prepared by precipitation?

Lead (ll) trioxocarbonate (lV)

Barium trioxocarbonate (IV)

Sodium trioxocarbnate (IV)

Calcium trioxocarbonate (IV)

View answer & explanation

Correct answer is C

No explanation has been provided for this answer.

919.

The alloy used extensively in the building industry is

steel

bronze

duralumin

type metal

View answer & explanation

Correct answer is A

No explanation has been provided for this answer.

920.

Which of the following pairs of salts undergo hydrolysis?

AlCI₃ and NH₄CI

AICI₃ and NaCI

FeCI₃ and KCI

Na₂SO₄ and K₂ SO₄

View answer & explanation

Correct answer is A

Salt hydrolysis is a reaction in which one of the ions from a salt reacts with water, forming either an acidic or basic solution.Salts can be hydrolyzed in water, If the salts at least consist of one weak base or weak acid, they can be hydrolyzed. On the other hand, if the salts are from a strong base and acid, they cannot be hydrolyzed.
Al and $NH_4$ are from weak base $Al(OH)_3$ and $NH_4OH$ respectively while Cl is from a strong acid HCl