WAEC Chemistry Past Questions & Answers - Page 176

877.

Consider the reaction: 2AI(s) + 6H+ (aq) → 2AI3+ (aq) + 3H2(g). What is the total number of moles of electrons transferred from the aluminium atoms to the hydrogen ions?

A.

3

B.

4

C.

5

D.

6

Correct answer is D

2AL(s) + 6H +(aq) → 2AL3+(aq) + 3H2(g). One aluminium atom transfers 3 electrons :. Two aluminium atoms will transfer 2x3=6 electrons

878.

Metals can be extracted from their ores by a process involving

A.

reduction

B.

oxidation

C.

hydrolysis

D.

decomposition

Correct answer is A

No explanation has been provided for this answer.

879.

The oxidation number of iodine in the iodate ion (IO -3) is

A.

-5

B.

-1

C.

+1

D.

+5

Correct answer is D

1O3
[oxidation number of 1] + [oxidation number of 0] x 3 = -1
x + -2 x 3 = 1
x - 6 = - 1
x = - 1 + 6 = +5

880.

Electrolysis is applied in the following processes except

A.

electroplating

B.

extraction of aluminium

C.

extraction of iron

D.

purification of copper

Correct answer is C

No explanation has been provided for this answer.