Empirical and Molecular Formulas

• Caffeine is 49.48% C, 5.15% H, 28.87% N and 16.49% O. What is its empirical formula?

Empirical Mass=

Empirical to molecular

• Since the empirical formula is the lowest ratio the actual molecule would weigh more.

• By a whole number multiple.• Divide the actual molar mass by the molar

mass of the empirical formula you calculated.

• You will then use the answer and multiply your empirical formula by it.

Caffeine has a molar mass of 194 g. what is its molecular formula?

• Find x if massformulaempirical

massmolarx

194 g

97 g= 1.99 = 2

C4H5N2O1C8H10N4O2

Molecular Formula 2 X

Example• A compound is known to be composed of

71.65 % Cl, 24.27% C and 4.07% H. Its molar mass is known (from gas density) is known to be 98.96 g. What is its molecular formula?

Example• A compound is known to be composed of

71.65 % Cl, 24.27% C and 4.07% H. Its molar mass is known (from gas density) is known to be 98.96 g. What is its molecular formula?

Its molar mass is known (from gas density)

is known to be 98.96 g. What is its molecular

formula?

•

would give an empirical wt of 48.5g/mol

massformulaempirical

massmolarx

g

g

5.48

96.98= 2=

1. What’s the empirical formula of a molecule containing 65.5% carbon, 5.5% hydrogen, and 29.0% oxygen?

2. If the molar mass of the compound in problem 1 is 110 grams/mole, what’s the molecular formula?

3. What’s the empirical formula of a molecule containing 18.7% lithium, 16.3% carbon, and 65.0% oxygen?

4. If the molar mass of the compound in problem 3 is 73.8 grams/mole, what’s the molecular formula?