Percent Composition

Percent Composition of a Chemical Compound

Percent composition is a measure of the relative amounts of each element in a compound, expressed as a percentage of the total mass. It is useful for determining the empirical formula of a compound and for analyzing its composition. Here's how you can calculate the percent composition of any chemical compound:

Step 1: Determine the Molar Mass of the Compound

The molar mass of a compound is the sum of the molar masses of all the atoms in one mole of the compound. You can find the molar mass of each element in the periodic table and then calculate the molar mass of the compound.

Step 2: Calculate the Percent Composition

To find the percent composition of each element in the compound, divide the total mass of each element by the molar mass of the compound and multiply by 100%.

The formula for percent composition is:

$Percent composition of an element = (Molar mass of the compound Total mass of the element in the compound) \times 100%$

Example: Percent Composition of Water (H₂O)

Calculate the Molar Mass of Water:
- Molar mass of hydrogen (H) = 1.01 g/mol
- Molar mass of oxygen (O) = 16.00 g/mol
- Molar mass of H₂O = 2(1.01 g/mol) + 1(16.00 g/mol) = 18.02 g/mol
Calculate the Percent Composition:
- Percent composition of hydrogen in H₂O: $Percent H = (18.02 g/mol 2 \times 1.01 g/mol) \times 100% \approx 11.21%$
- Percent composition of oxygen in H₂O: $Percent O = (18.02 g/mol 16.00 g/mol) \times 100% \approx 88.79%$

Conclusion

The percent composition of water (H₂O) is approximately 11.21% hydrogen (H) and 88.79% oxygen (O) by mass. You can use the same steps to calculate the percent composition of any chemical compound.