- Shows the actual number of atoms of each element in a molecule.
- Example: a compound contains 40.00% Carbon, 6.73% hydrogen and 53.27% oxygen by mass.
- Determine the empirical formula:
- C= 40/12.01=3.33
- O=53.27/16.00= 3.33
- Ratio is 3.33:6.66:3.33 = 1:2:1
- therefore empirical formula is CH20
- Molecular formula can be obtained from the empirical formula if the molar mass of the compound is also known
- CH2O = 12.01+ 1.01+ 1.01+ 16.00 = 30
- Mr = 60
- Molecular formula is C2H4O2
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