Percent Composition by Mass Worksheet
Calculate the percent composition by mass for various chemical compounds, including elements, water, and common salts. Reinforce understanding of chemical formulas and atomic weights.
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Percent Composition by Mass
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Read each question carefully and calculate the percent composition by mass for each element in the given compounds. Show all your work. Use the following approximate atomic masses: H=1.01 g/mol, C=12.01 g/mol, O=16.00 g/mol, Na=22.99 g/mol, Cl=35.45 g/mol, K=39.10 g/mol, S=32.07 g/mol, Fe=55.85 g/mol, N=14.01 g/mol, Ca=40.08 g/mol.
1. Calculate the percent composition by mass of Hydrogen and Oxygen in water (H₂O).
2. Determine the percent composition by mass of Sodium and Chlorine in Sodium Chloride (NaCl).
3. The formula for percent composition by mass is (mass of element / total mass of compound) x .
4. If a compound contains 20 grams of Carbon and 80 grams of Oxygen, the total mass of the compound is grams.
5. A compound has the formula K₂SO₄. Calculate the percent composition by mass of Potassium, Sulfur, and Oxygen.
6. What is the percent composition by mass of Iron and Oxygen in Iron(III) oxide (Fe₂O₃)?
7. Which of the following compounds has the highest percent by mass of Oxygen?
CO
CO₂
H₂O
SO₂
8. A sample of an unknown compound is found to contain 6.54 grams of Calcium, 3.48 grams of Nitrogen, and 11.96 grams of Oxygen. What is the percent composition by mass of each element in this compound?
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