WAEC Chemistry Past Questions & Answers - Page 90

446.

When salt loses its water of crystallization to the atmosphere on exposure, the process is said to be

efflorescence

déliquescence

effervescence

fluorescence

Correct answer is A

Efflorescence is a process of long exposure to the atmosphere which favors salt loss of water. Options B, C, D are not related to loss of water

447.

A small quantity of solid ammonium chloride (NH4Cl) heated gently in a test tube, the solid gradually disappear produce two gases. Later, a white cloudy deposit was absence on the cooler part of the test tube. The ammonium chloride is to have undergo

distillation

sublimation

precipitation

evaporation

View answer & explanation

Correct answer is B

Sublimation is the transformation of solid gaseous state without passing through the liquid state. Options A,C,D do not show case these character of sublimation as they do not bye pass states. They are in a particular order

448.

The acid in electrolysis of water is dilute

HNO₃

CH₃COOH

H₂SO₄

HCl

View answer & explanation

Correct answer is C

HeSO4 is the acid used in the electrolysis of water. Option A,B,D are concentrated acid and they will react with the water

449.

Vulcanization involve the removal of

monometer

the single bond

the double bond

a polymer

View answer & explanation

Correct answer is C

Vulcanizer is the removal of double bend in a chemical reaction. Option A,B,D can not be removed by vulcanizer

450.

The gas that is most useful in protecting humans against solar marathon is

chlorine

ozone

carbon IV oxide

hydrogen sulphide

View answer & explanation

Correct answer is B

The ozone layer or ozone shield refers to a region of Earth's stratosphere that absorbs most of the Sun's ultraviolet (UV) radiation. It contains high concentrations of ozone (O3) relative to other parts of the atmosphere, although still very small relative to other gases in the stratosphere