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WAEC Chemistry 2014 Paper

Question : 14

Total: 45

Solution:

Concept:

The mole ratio is found by converting each gas’s mass to its number of moles using its molar mass.

Explanation:

Hydrogen exists as

\mathrm{H}_2

, so its molar mass is

2 \times 1.00 = 2.00\ \text{g/mol}

Oxygen exists as

\mathrm{O}_2

, so its molar mass is

2 \times 16.0 = 32.0\ \text{g/mol}

Moles of hydrogen:

\text{Moles of } \mathrm{H}_2 = \frac{0.256}{2.00} = 0.128\ \text{mol}

Moles of oxygen:

\text{Moles of } \mathrm{O}_2 = \frac{2.00}{32.0} = 0.0625\ \text{mol}

Now write the ratio and simplify:

0.128 : 0.0625

Divide both sides by

0.0625

\frac{0.128}{0.0625} : \frac{0.0625}{0.0625} = 2 : 1

Answer:

The mole ratio of hydrogen to oxygen is

2:1

, which is option B.

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