The Molecular Formula Chemistry 11 Ms. McGrath

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.

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?

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

Determining a Molecular Formula You try page 97, #17 - 19