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WAEC Chemistry Past Questions & Answers - Page 18

86.

Oxochlorate(I) acid is used as a bleaching agent because it is

A.

a weak acid

B.

a reducing agent.

C.

an oxidizing agent

D.

a strong acid.

Correct answer is C

HOCl is unstable and decomposes to release oxygen which oxidizes the dye to form a colourless compound.

87.

Determine the quantity of electricity used when a current of 0.20 amperes is passed through an electrolytic cell for 60 minutes.

A.

12C

B.

120C

C.

360C

D.

720C

Correct answer is D

Q =It
t = 60 * 60=3600
I = 0.20
Q=0.20 * 3600
Q= 720C

88.

The products of the electrolysis of dilute sodium chloride using carbon electrodes are

Anode Cathode

A.

chlorine and sodium.

B.

oxygen and hydrogen.

C.

chlorine and hydrogen.

D.

hydrogen and oxygen.

Correct answer is B

Oxygen is produced at the anode and hydrogen is produced at the cathode in dilute NaCl

89.

If 60 g of M combines with 24 g of oxygen, what would the empirical formula of the oxide be?

( molar mass of M = 120, O = 16)

A.

MO

B.

MO2

C.

MO3

D.

MO4

Correct answer is C

Data obtained from the question
M = 60 g
O = 24 g
Empirical formula =?
How to determine the empirical formula
Divide by their molar mass
M = 60÷120 = 0.5
O = 24 ÷16 = 1.5
Divide by the smallest
M = 0.5÷0.5 = 1
O = 1.5 ÷0.5 = 3
Thus, the empirical formula of the oxide is MO₃

90.

Which of the following statements about the standard hydrogen electrode is not correct?

A.

The hydrogen gas is at a pressure of 1 atmosphere

B.

A solution containing 1 mol dm-3 of H+ (aq) ions is used

C.

A platinum electrode is used

D.

The temperature is kept at 20 °C

Correct answer is D

The standard hydrogen electrode consists of hydrogen gas at 25oC