WAEC Chemistry Past Questions & Answers - Page 82

406.

Consider the following half-cell reactions.
Al(s) \(\to\) Al3+(aq) + 3e-
Cu2+(aq) + 2e- \(\to\) Cu(s)

The overall equation for the reaction is

A.

Al(s) + Cu2+(aq) \(\to\) Al3+(aq) + Cu(s)

B.

2Al(s) + Cu2+(aq) \(\to\) 2Al(aq) + Cu(s)

C.

2Al(s) + 3Cu2+(aq) \(\to\) 3Cu(s) + 2Al3+(aq)

D.

3Al(s) + 2Cu2+(aq) \(\to\) Cu(s) + 3Al3+(aq)

Correct answer is C

Al(s) \(\to\) Al3+(aq) + 3e- ______(i)
Cu2+(aq) + 2e- \(\to\) Cu(s) ________(ii)

To balance the electrons, multiply equation (i) by 2 and equation (ii) by 3 and then add the resulting equations

2Al(s) \(\to\)2Al3+(aq) + 3e-
3cu2+(aq) + 6e- \(\to\)3Cu(s)
2Al(s) + 3Cu2+(aq) \(\to\) 3Cu(s) + 2Al3+(aq)

408.

The oxidation number of sulphur is +4 in

A.

Na2S>2O3

B.

H2SO3

C.

H2SO4

D.

SO3

Correct answer is B

No explanation has been provided for this answer.

409.

Which of the following substances is a non-electrolyte?

A.

H2SO4

B.

CH3COOH

C.

C6H12O6

D.

NH4Cl

Correct answer is C

No explanation has been provided for this answer.

410.

Chlorine water is used as a bleaching agent because it is

A.

An acidic solution

B.

An alkaline solution

C.

An oxidizing agent

D.

A reducing agent

Correct answer is C

No explanation has been provided for this answer.