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# Percent Composition Formula

The percent composition gives the number of grams of an element present in the compound per 100g of the compound; the formula gives the relative number of moles of an element in one mole of the compound.

Percent Composition Formula calculates the relative masses of each of the elements in a substance expressed as a percentage of total mass of the substance.

For example, the formula given below is used to calculate the percent composition for the element X.

 Related Calculators Mass Percent Composition Calculator Percent Change Ratio to Percent Adding Percent Calculator

## Percent Composition Problems

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Solved examples based on the percent composition is given below.

### Solved Examples

Question 1: What is the percent composition of chromium in K2Cr2O7?
Solution:

The formula weight of K2Cr2O7 is

2(39g/mol) + 2(52g/mol) + 7(16g/mol) = 294g/mol

% Composition of Cr = $\frac{2 \times 52}{294} \times$ 100%

% Composition of Cr = 35.4%

Question 2: Combustion of a 0.3037g sample of a certain compound yielded 1.0441g of CO2 and 0.1708g of H2O. What is the percent composition of the compound?
Solution:

The carbon in CO2 is 12/44 of the mass of the CO2 and the hydrogen in H2O is 2/18 of the mass of the H2O.

Therefore mass of carbon in the CO2 = $\frac{12 \times 1.0441}{44}$ = 0.2848g

and mass of hydrogen in the H2O = $\frac{2 \times 0.1708}{18}$ = 0.01898g

Thus % carbon in the sample = $\frac{0.2848 \times 100}{0.3037}$ = 93.7%

and % hydrogen in the sample = $\frac{0.01898 \times 100}{0.3037}$ = 6.25%

*AP and SAT are registered trademarks of the College Board.