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Percent Composition worksheet

Grades 10–11

Solve each problem and show your work. Round answers to 2 decimal places where needed.

1.
Problem 1.
- Calculate: Mass percent of a solute in a solution
- Second value you know: Mass of solvent
- Mass of solute: 34
- Mass of solvent: 110
Find: Mass percent of solute (w/w)
Answer
2.
Problem 2.
- Calculate: Mass percent of each element in a compound
- Chemical formula: H2SO2
Find: Sulfur (S), largest share
Answer
3.
Problem 3.
- Calculate: Mass percent of each element in a compound
- Chemical formula: H1SO2
Find: Sulfur (S), largest share
Answer
4.
Problem 4.
- Calculate: Mass percent of each element in a compound
- Chemical formula: H1SO4
Find: Oxygen (O), largest share
Answer
5.
Problem 5.
- Calculate: Mass percent of a solute in a solution
- Second value you know: Mass of solvent
- Mass of solute: 18
- Mass of solvent: 90
Find: Mass percent of solute (w/w)
Answer
6.
Problem 6.
- Calculate: Mass percent of a solute in a solution
- Second value you know: Total mass of solution
- Mass of solute: 24
- Total mass of solution: 150
Find: Mass percent of solute (w/w)
Answer
7.
Problem 7.
- Calculate: Mass percent of each element in a compound
- Chemical formula: H3SO5
Find: Oxygen (O), largest share
Answer
8.
Problem 8.
- Calculate: Mass percent of each element in a compound
- Chemical formula: H2SO1
Find: Sulfur (S), largest share
Answer
9.
Problem 9.
- Calculate: Mass percent of a solute in a solution
- Second value you know: Total mass of solution
- Mass of solute: 30
- Total mass of solution: 150
Find: Mass percent of solute (w/w)
Answer
10.
Problem 10.
- Calculate: Mass percent of a solute in a solution
- Second value you know: Total mass of solution
- Mass of solute: 29
- Total mass of solution: 150
Find: Mass percent of solute (w/w)
Answer

Answer key: Percent Composition worksheet

1. Mass percent of solute (w/w): 23.61%
1. Add the solute and solvent masses to get the mass of the solution
  $34 + 110$ $= 144$
2. Divide the solute mass by the whole solution's mass, then multiply by 100 to make a percent
  $mass %$ $= \frac{34}{144} \times 100$ $= 23.611111%$
2. Sulfur (S), largest share: 48.52%
1. Find the weight of one mole of H2SO2: for each element, multiply its number of atoms by its atomic weight, then add them up
  $2 \times 1.008 + 1 \times 32.06 + 2 \times 15.999$ $= 66.074 g/mol$
2. Hydrogen: divide its part of the weight by the total, then multiply by 100 for a percent
  $\frac{2.016 g/mol}{66.074 g/mol} \times 100$ $= 3.051124%$
3. Sulfur: divide its part of the weight by the total, then multiply by 100 for a percent
  $\frac{32.06 g/mol}{66.074 g/mol} \times 100$ $= 48.521355%$
4. Oxygen: divide its part of the weight by the total, then multiply by 100 for a percent
  $\frac{31.998 g/mol}{66.074 g/mol} \times 100$ $= 48.427521%$
3. Sulfur (S), largest share: 49.27%
1. Find the weight of one mole of H1SO2: for each element, multiply its number of atoms by its atomic weight, then add them up
  $1 \times 1.008 + 1 \times 32.06 + 2 \times 15.999$ $= 65.066 g/mol$
2. Hydrogen: divide its part of the weight by the total, then multiply by 100 for a percent
  $\frac{1.008 g/mol}{65.066 g/mol} \times 100$ $= 1.549196%$
3. Sulfur: divide its part of the weight by the total, then multiply by 100 for a percent
  $\frac{32.06 g/mol}{65.066 g/mol} \times 100$ $= 49.273046%$
4. Oxygen: divide its part of the weight by the total, then multiply by 100 for a percent
  $\frac{31.998 g/mol}{65.066 g/mol} \times 100$ $= 49.177758%$
4. Oxygen (O), largest share: 65.93%
1. Find the weight of one mole of H1SO4: for each element, multiply its number of atoms by its atomic weight, then add them up
  $1 \times 1.008 + 1 \times 32.06 + 4 \times 15.999$ $= 97.064 g/mol$
2. Hydrogen: divide its part of the weight by the total, then multiply by 100 for a percent
  $\frac{1.008 g/mol}{97.064 g/mol} \times 100$ $= 1.03849%$
3. Sulfur: divide its part of the weight by the total, then multiply by 100 for a percent
  $\frac{32.06 g/mol}{97.064 g/mol} \times 100$ $= 33.029754%$
4. Oxygen: divide its part of the weight by the total, then multiply by 100 for a percent
  $\frac{63.996 g/mol}{97.064 g/mol} \times 100$ $= 65.931756%$
5. Mass percent of solute (w/w): 16.67%
1. Add the solute and solvent masses to get the mass of the solution
  $18 + 90$ $= 108$
2. Divide the solute mass by the whole solution's mass, then multiply by 100 to make a percent
  $mass %$ $= \frac{18}{108} \times 100$ $= 16.666667%$
6. Mass percent of solute (w/w): 16%
1. Divide the solute mass by the whole solution's mass, then multiply by 100 to make a percent
  $mass %$ $= \frac{24}{150} \times 100$ $= 16%$
7. Oxygen (O), largest share: 69.51%
1. Find the weight of one mole of H3SO5: for each element, multiply its number of atoms by its atomic weight, then add them up
  $3 \times 1.008 + 1 \times 32.06 + 5 \times 15.999$ $= 115.079 g/mol$
2. Hydrogen: divide its part of the weight by the total, then multiply by 100 for a percent
  $\frac{3.024 g/mol}{115.079 g/mol} \times 100$ $= 2.62776%$
3. Sulfur: divide its part of the weight by the total, then multiply by 100 for a percent
  $\frac{32.06 g/mol}{115.079 g/mol} \times 100$ $= 27.859123%$
4. Oxygen: divide its part of the weight by the total, then multiply by 100 for a percent
  $\frac{79.995 g/mol}{115.079 g/mol} \times 100$ $= 69.513117%$
8. Sulfur (S), largest share: 64.02%
1. Find the weight of one mole of H2SO1: for each element, multiply its number of atoms by its atomic weight, then add them up
  $2 \times 1.008 + 1 \times 32.06 + 1 \times 15.999$ $= 50.075 g/mol$
2. Hydrogen: divide its part of the weight by the total, then multiply by 100 for a percent
  $\frac{2.016 g/mol}{50.075 g/mol} \times 100$ $= 4.025961%$
3. Sulfur: divide its part of the weight by the total, then multiply by 100 for a percent
  $\frac{32.06 g/mol}{50.075 g/mol} \times 100$ $= 64.023964%$
4. Oxygen: divide its part of the weight by the total, then multiply by 100 for a percent
  $\frac{15.999 g/mol}{50.075 g/mol} \times 100$ $= 31.950075%$
9. Mass percent of solute (w/w): 20%
1. Divide the solute mass by the whole solution's mass, then multiply by 100 to make a percent
  $mass %$ $= \frac{30}{150} \times 100$ $= 20%$
10. Mass percent of solute (w/w): 19.33%
1. Divide the solute mass by the whole solution's mass, then multiply by 100 to make a percent
  $mass %$ $= \frac{29}{150} \times 100$ $= 19.333333%$