WAEC Chemistry Past Questions & Answers - Page 226

1,126.

Which of the following can be added to dissolve the precipitate formed in the reaction represented by the following equation? CaCl2(aq) + H2C2O 4(s) ⇌ CaC 2O2

A.

Calcium chloride solution

B.

Concentrated hydrochloric acid

C.

Ethanol

D.

Ethanedioc acid

E.

Aqueous ammonia

Correct answer is E

No explanation has been provided for this answer.

1,127.

Pipe-borne water is usually chlorinated in order to

A.

improve the teste of the water

B.

remove the hardness in the water clear

C.

coagulate sediments in the water

D.

kill harmful bacteria in the water

E.

make the water clear and colourless

Correct answer is D

No explanation has been provided for this answer.

1,128.

Substances which absorb water from the atmosphere without dissolving in it are sid to be

A.

anhydrous

B.

hygroscopic

C.

insolube

D.

hydrated

E.

efflorescent

Correct answer is B

No explanation has been provided for this answer.

1,129.

How many electrons are removed from Cr2- when it is oxidized to CrO42-?

A.

0

B.

2

C.

4

D.

8

E.

10

Correct answer is D

From Cr2- to CrO42- involves 8 electrons to give oxidation state of Cr is +6

1,130.

What mass of copper would be deposited by a current of 1. 0 ampere passing for 965 seconds through copper (ll) tetraoxosulphate (IV) solution? [Cu = 63.5; 1F = 96500C]

A.

0.318g

B.

0.635g

C.

18g

D.

6.35g

E.

9.65g

Correct answer is A

Cu2+ + 2e- → Cu, From the equation 2 Faraday will liberate 63.5gm of copper The quantity of electricity passed (Q) Q = 1. 0 965 = 965 coulomb :. 2 x 96500 → 63.5, 965 → x. x = 965 / 2x96500 x 63.5 = 0.3175g \(\approx\) 0.328