Empirical Formula Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Empirical Formula.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

The simplest whole-number ratio of atoms of each element present in a compound, found by reducing the actual atom counts.

The reduced fraction of atoms—smallest numbers that show the ratio.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Shows the ratio of elements, not the actual number of atoms per molecule.

Common stuck point: Different compounds can share the same empirical formula — glucose and acetic acid both give CH₂O.

Worked Examples

Example 1

medium
A compound contains 40.0\% C, 6.7\% H, and 53.3\% O by mass. Determine the empirical formula.

Solution

  1. 1
    Assume 100 g: C = 40.0 g, H = 6.7 g, O = 53.3 g.
  2. 2
    Convert to moles: C = \frac{40.0}{12.01} = 3.33, H = \frac{6.7}{1.008} = 6.65, O = \frac{53.3}{16.00} = 3.33.
  3. 3
    Divide by smallest (3.33): C = 1, H = 2, O = 1.
  4. 4
    Empirical formula: \text{CH}_2\text{O}.

Answer

\text{CH}_2\text{O}
The empirical formula represents the simplest whole-number ratio of atoms. The molecular formula may be a multiple of the empirical formula (e.g., glucose \text{C}_6\text{H}_{12}\text{O}_6 has the same empirical formula \text{CH}_2\text{O}).

Example 2

hard
A compound has empirical formula \text{CH}_2\text{O} and a molar mass of 180\,\text{g/mol}. Find the molecular formula.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

medium
A compound is 72.0\% Mg and 28.0\% N. Find the empirical formula.

Example 2

medium
A compound is 40.0\% carbon, 6.7\% hydrogen, and 53.3\% oxygen by mass. What is its empirical formula?
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Background Knowledge

These ideas may be useful before you work through the harder examples.

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