1. Determine the molar mass of the compound.
- Add up the atomic masses of all the atoms in the compound.
2. Determine the mass of oxygen in the compound.
- Multiply the atomic mass of oxygen (15.999 g/mol) by the number of oxygen atoms in the compound.
3. Calculate the percent of oxygen by mass.
- Divide the mass of oxygen in the compound by the molar mass of the compound, then multiply by 100%.
Formula:
% oxygen by mass = (mass of oxygen in compound / molar mass of compound) * 100%
Example:
For glucose (C6H12O6), the molar mass is:
(6 x 12.011 g/mol) + (12 x 1.008 g/mol) + (6 x 15.999 g/mol) = 180.156 g/mol
The mass of oxygen in glucose is:
6 x 15.999 g/mol = 95.994 g/mol
The percent of oxygen by mass is:
% oxygen by mass = (95.994 g/mol / 180.156 g/mol) * 100% = 53.29%
Therefore, oxygen accounts for approximately 53.29% of the mass of glucose.
