Percent Composition Chemistry Example 1

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easy

Calculate the percent composition by mass of each element in

\text{H}_2\text{O}

1
Molar mass of $\text{H}_2\text{O} = 2(1.008) + 16.00 = 18.02\,\text{g/mol}$ .
2
%H $= \frac{2(1.008)}{18.02} \times 100\% = \frac{2.016}{18.02} \times 100\% = 11.19\%$ .
3
%O $= \frac{16.00}{18.02} \times 100\% = 88.81\%$ .

Answer

\text{H: } 11.19\%,\quad \text{O: } 88.81\%

Percent composition tells us the mass fraction of each element in a compound. The percentages must add up to 100% (within rounding error).

About Percent Composition

Percent composition is the percentage by mass of each element in a chemical compound.

Calculate the percent by mass of nitrogen in ammonium nitrate ([formula]).

What is the percent composition of carbon in [formula]? (C = 12.01, O = 16.00)

What percent by mass of calcium carbonate ([formula]) is oxygen? (Ca = [formula], C = [formula], O =