WAEC Chemistry Past Questions & Answers - Page 117

581.

When a substance changes directly from the solid state to the gaseous state without forming a liquid, the substance is said to

A.

condense

B.

evaporate

C.

sublime

D.

precipitate

Correct answer is C

No explanation has been provided for this answer.

582.

The volume occupied by 0.4 g of hydrogen gas at s.t.p. is [H = 1. 00; Molar volume at s.t.p. = 22.4 dm3]

A.

2.24 dm3

B.

4.48dm3

C.

22.4dm3

D.

44.8dm 3

Correct answer is B

2g of H\(_2\) = 22.4 dm\(^3\)

0.4g of H\(_2\) = x,

x = \(\frac{0.4 \times 22.4}{2}\) = 4.48dm\(^3\)

583.

Which of the following metals would readily displace hydrogen from steam?

A.

Copper

B.

Lead

C.

Magnesium

D.

Silver

Correct answer is C

In the electrochemical series, H\(^+\) is above all the other elements in the series except Magnesium. Hence, only Mg\(^{2+}\) can displace hydrogen from a reaction.

584.

A metal M forms two types of chlorine, MCl\(_2\) and MCl\(_3\) which of the following laws best explains the relationship between the chlorides? Law of

A.

conservation of mass

B.

definite proportion

C.

multiple proportion

D.

reciprocal proportion

Correct answer is C

Law of multiple proportions, statement that when two elements combine with each other to form more than one compound, the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers.

585.

A sample of a gas may be identified as chlorine if it turns

A.

damp blue litmus paper red

B.

lime water miky

C.

lead ethanoate paper black

D.

starch iodide paper blue-black

Correct answer is D

A test for chlorine is to place damp starch-iodide paper into a test tube of chlorine. A positive result for chlorine is indicated by the paper turning from white to blue-black.