Practice Molecular Formula in Chemistry

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

Quick Recap

The chemical formula showing the actual number of atoms of each element in one molecule of a compound, as opposed to the empirical formula which shows only the simplest ratio.

The real count of atoms, not just the ratio — it tells you exactly what the molecule contains.

Example 1

easy
Explain the difference between an empirical formula and a molecular formula. Give an example where they differ.

Example 2

medium
A compound has an empirical formula of \text{NO}_2 and a molar mass of 92\,\text{g/mol}. Determine the molecular formula. (N = 14.01, O = 16.00)

Example 3

medium
A compound is 40% C, 6.7% H, 53.3% O by mass. Its molar mass is 180 g/mol. Find the molecular formula.

Example 4

medium
A compound has empirical formula \text{CH} and molar mass 78\,\text{g/mol}. Find the molecular formula. (C = 12.01, H = 1.008)

Example 5

hard
A compound is 85.7\% C and 14.3\% H by mass, with a molar mass of 56.0\,\text{g/mol}. Determine both the empirical and molecular formulas.
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