1. Percent Composition Calculations
Percentage Composition: is the relative mass that each element contributes to a compound.
Percent Composition = Mass of Element X 100
Mass of Compound

2. Calculate from Sample Data-
1. Divide the element mass by total mass.
2. Multiply by 100.
3. Round
4. Repeat for all elements in the compound.
Example- A sample weights 3.74 g. It is analyzed to contain 1.10 g C, g S and g O. Calculate the percent composition.

3. Calculate from a Formula
1. Calculate the molar mass.
2. Divide the mass of an element by the molar mass.
3. Multiply by 100.
4. Round
5. Repeat for all elements in the compound.
Example- Calculate the percent composition of copper (II) nitrate.

4. In mass Calculations
1. Calculate the percent composition of the elements needed.
2. Multiply the total sample mass by the percent of the element (change to decimal).
3. Round to correct significant figures.
4. Grams is the correct unit for mass.
Example- What mass of silver is found in a 125 g sample of silver sulfide?

5. What percent of sodium chloride is made from sodium. If you have 45
What percent of sodium chloride is made from sodium? If you have 45.5 g of total substance and find that 40.0 g are carbon and 5.5 g are hydrogen, what are their percents? If a sample is 25% nitrogen and 75% oxygen, how many grams of each is present in 25.0 g total?