Calculating Percentage Composition

% Composition: percentage by mass of each atom in a formula or compound.


Example: Determine the % composition of each atom in glucose, C6H12O6

Steps to Solve:

1. List all elements in the compound for which you would like to determine the percentage composition.




2. Calculate the TOTAL mass of each element in the formula in small “chunks”.

C: (6 atoms of C) x (12 g) = 72 g

H: (12 atoms of H) x (1 g) = 12 g

O: (6 atoms of O) x (16 g) = 96 g

3. Determine the formula weight (by adding all mass of each element)

72 g + 12 g + 96 g = 180 g

Related Byte: Calculating Formula Weight

4. Divide each element’s TOTAL mass by the formula weight, then multiply by 100 to attain the percentage.

C: C

H: H

O: O

Double check: the sum of all percentages (40% + 6.7% + 53.3%) = 100%!


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