How Do You Find the Percent Composition?

"Elemental analysis" is the term used for deriving the weight of an element in a compound--it is used in the field of chemistry. Another term for the purpose of elemental analysis is finding the percent composition, which is the percentage of weight an element represents in a compound. The most common elements the formula is used for are carbon, hydrogen and nitrogen. This is called CNH analysis and is used in organic chemistry. Finding the percent composition involves using a simple mathematical formula and performing straightforward calculations.

Things You'll Need

• Calculator
• Pencil (or pen)
• Paper
• Periodic Table of the Elements that lists atomic weight.

Instructions

Find Percent Composition

1. Find each element in your compound on the periodic table.

2. Write down the atomic weight of each element. For example C(arbon)'s atomic weight is 12.01 and O(xygen)'s is 16.

3. Add the total weight of each element in your compound to get the total (molar) mass of the compound. For example, the compound carbon dioxide has one carbon atom and two oxygen atoms. Add 12.01 + 2(16) to get the molar mass.

4. Divide the individual atomic mass of the element whose percent composition you are looking for by the total (molar) mass of the compound. For example, if you want to know the percent composition of carbon in carbon dioxide you divide 12.01 by 44.01 (total mass of carbon dioxide)

5. Multiply your result from Step 4 by 100 to receive the percentage composition of your element.

References

• Davidsion College: Elemental Analysis
• Texas A & M University :Stoichiometry : Percent Composition

Resources

• Boomeria website: Periodic Table of the Elements