Molecular Formulas

1
Molecular Formulas

• Empirical formula the smallest whole number
  ratio of elements
• Molecular formula the true number of elements
  in a compound

2
Steps for Calculating Molecular Formula

• Calculate the empirical formula
• Get the molecular mass of the empirical formula
  that you just determined
• Divide the experimentally determined molecular
  mass (given) by the molecular mass of the
  empirical formula
• You will get a whole number
• Multiply everything in the empirical formula by
  this number

3
Molecular Formula Problem

• Calculate the molecular formula of a compound
  containing 40.68C, 5.08H, and 54.25O with an
  experimentally determined molecular weight of
  118.1 g/mol

4
Molecular Formula Problem

• 40.68g C x 1 mol C 3.387 / 3.387 (1)2 2
• 12.01 g C
• 5.08g H x 1 mol H 5.04 / 3.387 (1.5)2 3
• 1.01 g H
• 54.25 g Ox 1 mol O 3.390 / 3.387 (1)2 2
• 16.00 g O
• C2H3O2

5
Molecular Formula Problem

• C2H3O2
• Molecular Mass 59.04
• EDMM / EFMM 118.1 / 59.04 2
• Molecular Formula
• C4H6O4

6
Molecular Formula Problem

• Calculate the molecular formula of a compound
  containing 57.84 g C, 3.64 g H, and 38.52 g O
  with an experimentally determined molecular mass
  of 249.21 g/mol
• C12H9O6