Percent Composition Practice Problems

Front

What is percent composition?

Back

Percent composition is the percentage by mass of each element in a compound, calculated by dividing the mass of each element by the total mass of the compound and multiplying by 100.

Front

How do you calculate the percent composition of a compound?

Back

To calculate percent composition, use the formula: (mass of element in 1 mole of compound / molar mass of compound) x 100.

Front

What is the percent composition of water (H2O)?

Back

H = 11.1%, O = 88.9%.

Front

What is the percent composition by mass of oxygen in MgSO4 (molar mass = 120 g/mol)?

Back

53%.

Front

Which element has a higher percent composition in MgBr2, magnesium or bromine?

Back

Bromine.

Front

What percentage of the total atomic mass of lithium phosphide (Li3P) is lithium?

Back

40%.

Front

What is the percent by mass of oxygen in NaOH?

Back

40%.

Front

What is the molar mass of water (H2O)?

Back

18 g/mol.

Front

If a compound has a molar mass of 100 g/mol and contains 20 g of carbon, what is the percent composition of carbon?

Back

20%.

Front

How does the percent composition relate to empirical and molecular formulas?

Back

Percent composition helps determine the empirical formula, which can be used to find the molecular formula if the molar mass is known.