WAEC Chemistry Past Questions & Answers

836.

Metals can be extracted from their ores by a process involving

reduction

oxidation

hydrolysis

decomposition

View answer & explanation

Correct answer is A

No explanation has been provided for this answer.

837.

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

-5

-1

View answer & explanation

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

838.

Electrolysis is applied in the following processes except

electroplating

extraction of aluminium

extraction of iron

purification of copper

View answer & explanation

Correct answer is C

No explanation has been provided for this answer.

839.

Consider the reaction represented by the equation: 2SO $_{2(g)}$ + O $_{2(g)}$ ⇌ 2SO $_{3(g)}$ ; ∆H = - 197 kJmol $^{-1}$ . Which of the following conditions will not increase the yield of sulphur (VI) oxide?

Increase in temperature

Decrease in temperature

Increase in pressure

Addition of O₂ into the mixture

View answer & explanation

Correct answer is A

The reaction is an exothermic reaction (∆H=-197kjmol).
For continual yield of sulphur(IV)oxide, heat must be liberated.
So,increasing the temperature of the reaction will lead to reduction in yield of $SO_3$ since it favours backward reaction which is endothermic.