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WAEC Chemistry 2012 Paper

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Question : 22

Total: 44

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]

2.24 dm³
4.48dm³
22.4dm³
44.8dm ³

Solution:

Concept:

At s.t.p., one mole of any gas occupies

22.4 \, \text{dm}^3

.

Hydrogen gas is diatomic,

\mathrm{H}_2

, with molar mass

2.00 \, \text{g}

.

Explanation:

Molar mass of

\mathrm{H}_2 = 2 \times 1.00 = 2.00 \, \text{g}

.

Volume occupied by

2.00 \, \text{g}

of

\mathrm{H}_2

at s.t.p. is

22.4 \, \text{dm}^3

.

Let

x

be the volume occupied by

0.40 \, \text{g}

of

\mathrm{H}_2

.

Therefore:

x = \frac{0.40 \times 22.4}{2.00} = 4.48 \, \text{dm}^3

Answer:

The volume occupied by

0.4 \, \text{g}

of hydrogen gas at s.t.p. is

4.48 \, \text{dm}^3

.

Correct option: B.

4.48 \, \text{dm}^3

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