Question

What is the percentage by mass of hydrogen in ethanoic acid?
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Answer 1

The molecular formula for ethanoic acid is CH3COOH.

The molar mass of the molecule is:

1 (carbon atom) x 12.01 g/mol = 12.01 g/mol
2 (hydrogen atoms) x 1.01 g/mol = 2.02 g/mol
2 (oxygen atoms) x 16.00 g/mol = 32.00 g/mol

Total molar mass = 46.03 g/mol

The mass of hydrogen in one molecule of ethanoic acid:

2 (hydrogen atoms) x 1.01 g/mol = 2.02 g/mol

So the percentage by mass of hydrogen in ethanoic acid is:

[(2.02 g/mol) / (46.03 g/mol)] x 100% = 4.39% (rounded to two decimal places)

Therefore, ethanoic acid contains 4.39% hydrogen by mass.