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WAEC Chemistry Past Questions & Answers - Page 66

326.

What is the solubility of a salt if 0.4g of it is obtained on evaporating 200 $cm^{3}$ of its saturated solution to dryness?

0.08 $gdm^{-3}$

2.00 $gdm^{-3}$

8.00 $gdm^{-3}$

80.00 $gdm^{-3}$

View answer & explanation

Correct answer is B

1000 $cm^{3}$ = 1 $dm^{3}$

200 $cm^{3}$ = 0.2 $dm^{3}$

⇒ 0.2 $dm^{3}$ contains 0.4g

hence, solubility of the salt which is the amount of the salt dissolvable in 1 $dm^{3}$ is

$\frac{0.4g}{0.2dm^{3}} = 2.0gdm^{-3}$

327.

The process of extraction of iron from its ore is

decomposition

oxidation

reduction

sublimation

View answer & explanation

Correct answer is C

The Iron is to to be gotten by the removal of oxygen from its ore, and this is called a reduction reaction.

328.

Which of the following equations represents a redox reaction?

$HNO_{{3}{(aq)}} + NaOH_{(aq)} \to NaNO_{{3}{(aq)}} + H_{2}O_{(l)}$

$AgNO_{{3}{(aq)}}+KCl_{(aq)} \to AgCl_{(s)}+KNO_{{3}{(aq)}}$

$CaCO_{{3}{(s)}} \to CaO_{(s)} + CO_{{2}{(g)}}$

$2H_{2}S_{(s)} + SO_{{2}{(g)}} \to 2HO_{2} + 3S_{(g)}$

View answer & explanation

Correct answer is D

No explanation has been provided for this answer.

329.

Which of the following raw materials is used in the plastic industry?

Ethene

Methane

Sulphur

Hydrogen

View answer & explanation

Correct answer is A

Ethene is the most important organic chemical, by weight, that is manufactured. It is an important raw material for the production of plastics and antifreeze solutions as well as solvents.

330.

The process that occurs when two equivalent forms of a compound are in equilibrium is

Isotopy

Resonance

Isomerism

Reforming

View answer & explanation

Correct answer is B

Resonance involves two forms of a compound.
Isomerism involves two or more forms of an element.
Reforming involves the rearrangement of molecule.

This deals with a two forms of a molecule where the chemical connectivity is the same but the electrons are distributed differently around the structure.