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WAEC Chemistry 2019 Paper

Question : 13

Total: 50

What is the percentage by mass of H in CH3COOH

Solution:

Concept:

Percentage by mass is the mass of hydrogen in one mole of the compound divided by the molar mass, multiplied by 100.

Explanation:

The formula

\mathrm{CH_3COOH}

contains 2 carbon atoms, 4 hydrogen atoms, and 2 oxygen atoms.

Molar mass of

\mathrm{CH_3COOH}

2(12) + 4(1) + 2(16) = 24 + 4 + 32 = 60\ \mathrm{g/mol}

Mass of hydrogen in one mole of the compound =

4(1) = 4\ \mathrm{g}

Percentage by mass of hydrogen =

\frac{4}{60} \times 100 = 6.67\%

This is approximately

6.7\%

Answer:

6.7\%

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