WAEC Chemistry Past Questions & Answers - Page 19

91.

The products of the electrolysis of dilute sodium chloride using carbon electrodes are

Anode Cathode

A.

chlorine and sodium.

B.

oxygen and hydrogen.

C.

chlorine and hydrogen.

D.

hydrogen and oxygen.

Correct answer is B

Oxygen is produced at the anode and hydrogen is produced at the cathode in dilute NaCl

92.

If 60 g of M combines with 24 g of oxygen, what would the empirical formula of the oxide be?

( molar mass of M = 120, O = 16)

A.

MO

B.

MO\(_{2}\)

C.

MO\(_{3}\)

D.

MO\(_{4}\)

Correct answer is C

Data obtained from the question
M = 60 g
O = 24 g
Empirical formula =?
How to determine the empirical formula
Divide by their molar mass
M = 60÷120 = 0.5
O = 24 ÷16 = 1.5
Divide by the smallest
M = 0.5÷0.5 = 1
O = 1.5 ÷0.5 = 3
Thus, the empirical formula of the oxide is MO₃

93.

Which of the following statements about the standard hydrogen electrode is not correct?

A.

The hydrogen gas is at a pressure of 1 atmosphere

B.

A solution containing 1 mol dm-3 of H+ (aq) ions is used

C.

A platinum electrode is used

D.

The temperature is kept at 20 °C

Correct answer is D

The standard hydrogen electrode consists of hydrogen gas at 25oC

94.

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.

95.

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.