Empirical Formula Calculator

Empirical Formula Calculator

What is an Empirical Formula?

The empirical formula of a chemical compound is the simplest whole-number ratio of atoms of each element present in that compound. It represents the "simplest" version of a formula, based on the relative proportions of its atoms.

For example, the molecular formula for glucose is C6H12O6. This tells you the exact number of atoms in one molecule. The empirical formula, however, is found by dividing all subscripts by their greatest common divisor (which is 6). This gives CH2O, which is the simplest 1:2:1 ratio of Carbon, Hydrogen, and Oxygen.

Empirical vs. Molecular Formula

• Empirical Formula: The simplest whole-number ratio of elements (e.g., CH2O).
• Molecular Formula: The actual number of atoms of each element in one molecule (e.g., C6H12O6).

Frequently Asked Questions

How do I find the molecular formula from the empirical formula?

To find the molecular formula, you need one more piece of information: the compound's molar mass.
1. Calculate the molar mass of your empirical formula (e.g., for CH2O, this is 12.01 + 2(1.008) + 16.00 = 30.03 g/mol).
2. Divide the compound's *actual* molar mass (given in the problem) by the empirical formula's mass. This will give you a whole number, 'n'.
3. Multiply all the subscripts in the empirical formula by 'n'.
Example: If the actual molar mass is 180.18 g/mol, then n = 180.18 / 30.03 ≈ 6. The molecular formula is (CH2O)6 = C6H12O6.

What is the Law of Definite Proportions?

The Law of Definite Proportions states that a given chemical compound always contains its component elements in a fixed ratio by mass, regardless of its source or method of preparation. For example, pure water (H2O) will *always* consist of 11.1% hydrogen and 88.9% oxygen by mass. This law is the fundamental reason why empirical formulas can be calculated from mass percentages.

Why did my calculation give a ratio of 1.5?

This is very common. When you divide by the smallest number of moles, you often get ratios with decimals like 1.33, 1.5, or 1.25. This simply means the simplest ratio isn't 1:1. You must multiply *all* ratios by a small integer to make them whole numbers.
• If you see x.5 (like 1.5), multiply everything by 2. (1.5 * 2 = 3)
• If you see x.33 or x.67 (like 1.33), multiply by 3. (1.33 * 3 ≈ 4)
• If you see x.25 or x.75, multiply by 4. (1.25 * 4 = 5)