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Percent Composition by Mass Worksheet
Show all work, including the correct units and sig figs with your answer.
Experimental Percent Composition by Mass
1. A chemist determines that 1.26 g of iron reacts with 0.54 g of oxygen to form rust. What is the percent
composition of each element in the new compound?
2. In the lab, a chemist analyzed a sample of methanol and found that it was made of 6.2 g of carbon, 4.1 g of
hydrogen, and 15.9 g of oxygen. What is the percent composition of each element?
3. In an experiment, a student took a 12.2 g sample of table sale and chemically separated the chlorine from the
sodium. He determined that there were 5.2 g of chlorine in the sample. What is the percent composition of
each element in the table salt?
4. A compound contains 1.2 moles of carbon and 3.2 moles of hydrogen. What is the percent composition by
mass of each element in the compound?
5. In an experiment, 0.05 moles of iron and 0.05 moles of sulfur are heated in a test tube to create a new
substance. What is the percent composition by mass of each element in the new compound?
6. A chemist breaks down a compound into 3.4 moles of carbon and 6.8 moles of oxygen. What is the percent
composition by mass of each element in the compound?
7. In an experiment, 2.0 moles of oxygen atoms reacts with 80.1 g of calcium to form a new compound. What is
the percent composition by mass of each element in the new compound?
