Molar MassMolar mass of ozone (O3)
The molar mass of ozone, O3, is 48.00 g/mol. One mole of it, which is 6.022 × 1023 molecules, has a mass of 48.00 grams.
48.00 g/mol
3 × 15.999 = 47.997 · 3 atoms in the formula · also called trioxygen
About ozone
Ozone is a form of oxygen with three atoms in each molecule. A layer of it high in the atmosphere absorbs harmful ultraviolet light.
Other names: trioxygen.
The working
The formula O3 has 3 oxygen atoms. Multiply each count by the atomic weight of the element and add:
| Element | Atoms | Atomic weight | Total | Share by mass |
|---|---|---|---|---|
| Oxygen (O) | 3 | 15.999 | 47.997 | 100.00% |
3 × 15.999 = 47.997 g/mol
With the rounded atomic masses used in many school books (O = 16) the answer is 48 g/mol. The difference from 48.00 is too small to matter in most school sums.
Percentage composition
O3 contains only oxygen, so oxygen makes up 100% of its mass. Each molecule has 3 atoms, which is why the molar mass is 3 times the atomic weight 15.999.
Worked examples
Grams to moles. How many moles are in 100 g of O3? Divide the mass by the molar mass: 100 ÷ 48.00 = 2.083 mol.
Moles to grams. What is the mass of 2 mol of O3? Multiply: 2 × 48.00 = 95.99 g.
Counting particles. 100 g contains 2.083 mol × 6.022 × 1023 = 1.255 × 1024 molecules, and 3.764 × 1024 atoms in all.
As a gas. At 0 °C and 1 atmosphere one mole of an ideal gas occupies 22.4 litres, so the density of O3 is about 48.00 ÷ 22.4 = 2.14 g per litre. Air averages about 29 g/mol, so this gas is heavier than air.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 4.8 g |
| 0.5 mol | 24 g |
| 1 mol | 48 g |
| 2 mol | 95.99 g |
| 5 mol | 240 g |
| Mass | Moles |
|---|---|
| 1 g | 0.02083 mol |
| 10 g | 0.2083 mol |
| 100 g | 2.083 mol |
| 1 kg | 20.83 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of O3?
The molar mass of ozone (O3) is 48.00 g/mol, or 47.997 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of O3?
100 ÷ 48.00 = 2.083 mol.
What is the mass of one molecule of O3?
Divide the molar mass by the Avogadro constant: 48.00 ÷ 6.022 × 1023 = 7.970 × 10-23 g.
Which values? This site uses the abridged standard atomic weights published by IUPAC (CIAAW), read on 12 November 2026. Your textbook or question paper may round them differently, for example H = 1 and O = 16, so its answer can differ slightly. In an exam, use the values the paper gives.