Question

Determine the empirical and molecular formulas of each of the following substances:

(a) Styrene, a compound substance used to make Styrofoam^® cups and insulation, contains 92.3% C and 7.7% H by mass and has a molar mass of 104 g/mol.

(b) Caffeine, a stimulant found in coffee, contains 49.5% C, 5.15% H, 28.9% N, and 16.5% O by mass and has a molar mass of 195 g/mol.

(c) Monosodium glutamate (MSG), a flavor enhancer in certain foods, contains 35.51% C, 4.77% H, 37.85% O, 8.29% N, and 13.60% Na, and has a molar mass of 169 g/mol.

Empirical formula of this compound is CH.

To determine the molecular formula, we need to find out how many times is molar mass higher than the mass of empirical formula:

Molecular formula is C₈H₈.

b) Empirical formula of caffeine:

Empirical formula of caffeine is C₄H₅N₂O. The sum of atomic masses from empirical formula is 97 g/mol.

Molecular formula of caffeine is 2 × empirical formula = C₈H₁₀N₄O₂

c) Empirical formula of MSG:

Empirical formula of MSG is C₅H₈NO₄Na. The sum of atomic masses of empirical formula is 169 g/mol, the same as molar mass. Empirical and molecular formula are identical.