Question

Acetic acid (HC2H3O2) is the active ingredient in vinegar. Calculate the mass percent composition of H in acetic acid.

Express the mass percent composition to four significant figures.

Answer 1

The molecular weight of acetic acid is:

2(12.01 g/mol) + 2(1.01 g/mol) + 4(16.00 g/mol) = 60.05 g/mol

The mass of one H atom in acetic acid is:

2(1.01 g/mol) = 2.02 g/mol

To calculate the mass percent composition of H in acetic acid, we divide the mass of H by the molecular weight of acetic acid, and then multiply by 100:

mass percent composition of H = (2.02 g/mol / 60.05 g/mol) x 100% = 3.36%

So that means, the mass percent composition of H in acetic acid is 3.36%, expressed to four significant figures.