Section 6.3

Formulas of Compounds

1. To understand the meaning of empirical formula

2. To learn to calculate empirical formulas

3. To learn to calculate the molecular formula of a compound

Objectives

Section 6.3

Formulas of Compounds

What is the Formula? mass spec

• If I analyze a compound by mass as 7.7% Hydrogen and 92.3 % Carbon what is its formula?

• If I have 100g of the compound how many grams do I have of each element?

• How many moles of each element do I have?• What is the simple number ratio between the two

numbers of moles?

• What is the formula?

• Is this the only possible formula?

Section 6.3

Formulas of Compounds

A. Empirical Formulas

• The empirical formula of a compound is the simplest whole number ratio of the atoms present in the compound.

What is the empirical formula of the following compounds?

• Sodium Peroxide Na2O2

• Terephthalic acid C8H6O4

• Phenobarbital C12H12N2O3

• 1,4-dichloro-2-butene C4H6Cl2

Section 6.3

Formulas of Compounds

B. Calculation of Empirical Formulas

Section 6.3

Formulas of Compounds

C. Calculation of Molecular Formulas

• The molecular formula is the exact formula of the molecules present in a substance.

• The molecular formula is always an integer multiple of the empirical formula.

Molecular formula = (empirical formula)n

where n is a whole number

Empirical Formula: CH

Molar Mass = 78

Molecular Formula?

Section 6.3

Formulas of Compounds

Formula Summary

For the sugar glucose