WAEC Chemistry Past Questions & Answers - Page 19

91.

Alkanols can be manufactured from alkenes by the initial reaction of alkenes with

A.

bromine in tetrachloromethane

B.

concentrated tetraoxosulphate(VI) acid

C.

aqueous potassium tetraoxomanganate(VII).

D.

sodium hydroxide solution.

Correct answer is B

An alkene reacts with conc. H2SO4 to yield an alkyl hydrogen tetraoxosulphate (VI). The compound formed undergoes hydrolysis when boiled with water to yield an alcohol.

92.

Which of the following compounds would react rapidly with bromine?

A.

Benzene

B.

Hexane

C.

Hexene

D.

Hexanol

Correct answer is C

The addition of bromine to most alkenes is so fast that when bromine is added dropwise to a solution of the alkene the red bromine color disappears almost immediately. In fact, this discharge of color is a useful qualitative test for alkenes.

93.

What amount of electricity is required to deposit one mole of aluminium from a solution of AlCl3?

A.

One Faraday

B.

One ampere

C.

Three Faradays

D.

Three amperes

Correct answer is C

AlCl3 → Al3+ + 3Cl-
At cathode:
Al3+ + 3e- → Al
3 mole of electrons corresponds 3 F charge
So, required charge =3 F

94.

The following compounds are condensation polymers except

A.

nylon

B.

protein

C.

starch

D.

polyethene

Correct answer is D

Condensation polymers are any kind of polymers whose process of polymerization involves a condensation reaction.

95.

The cleansing effect of soap is low in acidic water because of

A.

the formation of unionized fatty acid.

B.

increase in the pH of the soap molecules.

C.

anti-biodegradable effect of hydrogen ions

D.

the hardness of the acidic water.

Correct answer is A

Soaps cannot be used in acidic condition because they lose their cleansing effect due to the formation of long chain fatty acids