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JAMB Chemistry 2020 Paper

Question : 32

Total: 40

What mass of water is produced when 8.0g of hydrogen reacts with excess oxygen?

Solution:

Concept:

Use the balanced equation for hydrogen combustion to relate the mass of hydrogen to the mass of water produced.

Explanation:

The reaction is:

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

From the equation,

4\mathrm{g}

of hydrogen (from

2 \times 2\mathrm{g}

) produces

36\mathrm{g}

of water (from

2 \times 18\mathrm{g}

Therefore,

8.0\mathrm{g}

of hydrogen is double

4\mathrm{g}

So, mass of water produced is:

2 \times 36\mathrm{g} = 72\mathrm{g}

Answer:

72.0\mathrm{g}

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