Molecular Formulas

1. Find empirical formula

2. Calculate molar mass of empirical formula

3. Molar mass of compound / molar mass of empirical formula (we’ll call this the factor)

4. Multiply subscripts by factor to get molecular formula

Molecular Formula• A compound is found to have an empirical formula of

C2H3O2. The molar mass of the compound has 118.1 g/mol. What is the molecular formula?– Molar mass of C2H3O2

C2H3O2 = 2x12 + 3x1 + 2x16= 59 g/mol

– Molar mass of compound / molar mass of empirical118.1 / 59 = 2

464

xxx

232

222

OHC

OHC

Molecular Formula• A compound was found to contain 49.98 g

carbon and 10.47 g of hydrogen. The molar mass of the compound is 58.12g/mol. Determine the molecular formula

• C= 49.98 / 12 = 4.165 / 4.165 = 1 x 2 = 2• H= 10.47 / 1 = 10.47 / 4.165 = 2.5 x 2 = 5

• C2H5 = 2x12 + 5x1 = 29• 58.12 /29 = 2

C2H5x2 x2

C4H10

Molecular Formula Practice I1. Analysis of a chemical used in photographic

developing fluid indicates a chemical composition of 65.45% C, 5.45% H, and 29.09% O. The molar mass is found to be 110 g/mol. Determine the molecular formula.

Molecular Formula Practice I2. A compound was found to contain 49.98 g carbon

and 10.47 g hydrogen. The molar mass of the compound is 58.12 g/mol. Determine the molecular formula.

Molecular Formula Practice I3. A colorless liquid composed of 46.68% nitrogen

and 53.32% oxygen has a molar mass of 60.01 g/mol. What is the molecular formula?