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JAMB Chemistry 2012 Paper

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Question : 5

Total: 45

2H_2(g) + O_2(g) → 2H₂ O_(g)

In the reaction above, what volume of hydrogen would be left over when 300 cm³ of oxygen and 1000 cm³ of hydrogen are exploded in a sealed tube?

200 cm³
400 cm³
600 cm³
700 cm³

Solution:

Concept:

Reacting gas volumes are in the ratio of their coefficients in the balanced equation.

Explanation:

From

2\mathrm{H}_2 + \mathrm{O}_2 \rightarrow 2\mathrm{H}_2\mathrm{O}

, the ratio of hydrogen to oxygen is

2 : 1

.

Oxygen present is

300\text{ cm}^3

.

Hydrogen used is

2 \times 300 = 600\text{ cm}^3

.

Initial hydrogen is

1000\text{ cm}^3

.

Hydrogen left over is

1000 - 600 = 400\text{ cm}^3

.

Answer:

400\text{ cm}^3

, which is option B.

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