1. The Molecular Formula
Chemistry 11
Ms. McGrath

2. The Molecular Formula The empirical formula CH has a molar mass
of 13 g/mol.
Acetylene, C2H2, and benzene, C6H6 both
have the empirical formula CH.
Suppose its been determined through mass
spectrometry that a sample has a molar mass
of 78 g/mol. The compound must be C6H6,
since 6 x 13 g = 78 g.

3. Determining a Molecular Formula
The empirical formula for ribose is
CH2O. In an experiment, using a mass
spectrometer, the molar mass of ribose
was determined to be 150 g/mol. What
is the molecular formula for ribose?

4. Determining a Molecular Formula
The molar mass of the empirical formula
CH2O is 30 g/mol.
The molar mass of ribose is 150 g/mol.
150 g/mol = 5
30g/mol
Molecular formula subscripts = 5 x empirical formula
subscripts
= C1 x 5H2 x 5 O1 x 5
= C5H10O5

5. Determining a Molecular Formula
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