Molar MassMolar mass of nitrogen dioxide (NO2)
The molar mass of nitrogen dioxide, NO2, is 46.01 g/mol. One mole of it, which is 6.022 × 1023 molecules, has a mass of 46.01 grams.
About nitrogen dioxide
Nitrogen dioxide is a brown, poisonous gas seen when nitrates are heated or when copper reacts with concentrated nitric acid. It is a pollutant in vehicle exhaust.
The working
The formula NO2 has 1 nitrogen atom and 2 oxygen atoms, 3 atoms in all. Multiply each count by the atomic weight of the element and add:
| Element | Atoms | Atomic weight | Total | Share by mass |
|---|---|---|---|---|
| Nitrogen (N) | 1 | 14.007 | 14.007 | 30.45% |
| Oxygen (O) | 2 | 15.999 | 31.998 | 69.55% |
14.007 + 2 × 15.999 = 46.005 g/mol
With the rounded atomic masses used in many school books (N = 14, O = 16) the answer is 46 g/mol. The difference from 46.01 is too small to matter in most school sums.
Percentage composition
By mass, NO2 is 30.45% nitrogen and 69.55% oxygen. The largest share comes from oxygen. In a 100 g sample there are 30.4 g of nitrogen and 69.6 g of oxygen.
Worked examples
Grams to moles. How many moles are in 40 g of NO2? Divide the mass by the molar mass: 40 ÷ 46.01 = 0.8695 mol.
Moles to grams. What is the mass of 3 mol of NO2? Multiply: 3 × 46.01 = 138 g.
Counting particles. 40 g contains 0.8695 mol × 6.022 × 1023 = 5.236 × 1023 molecules, and 1.571 × 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 NO2 is about 46.01 ÷ 22.4 = 2.05 g per litre. Air averages about 29 g/mol, so this gas is heavier than air.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 4.601 g |
| 0.5 mol | 23 g |
| 1 mol | 46.01 g |
| 2 mol | 92.01 g |
| 5 mol | 230 g |
| Mass | Moles |
|---|---|
| 1 g | 0.02174 mol |
| 10 g | 0.2174 mol |
| 100 g | 2.174 mol |
| 1 kg | 21.74 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of NO2?
The molar mass of nitrogen dioxide (NO2) is 46.01 g/mol, or 46.005 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of NO2?
100 ÷ 46.01 = 2.174 mol.
What is the mass of one molecule of NO2?
Divide the molar mass by the Avogadro constant: 46.01 ÷ 6.022 × 1023 = 7.639 × 10-23 g.
What is the percentage of oxygen in NO2?
Oxygen makes up 69.55% of the mass of NO2: 2 × 15.999 ÷ 46.005 × 100.
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.