Molar MassMolar mass of ammonia (NH3)
The molar mass of ammonia, NH3, is 17.03 g/mol. One mole of it, which is 6.022 × 1023 molecules, has a mass of 17.03 grams.
About ammonia
Ammonia is a colourless gas with a sharp smell, made from nitrogen and hydrogen by the Haber process. Most of it goes into fertilisers. It is lighter than air and very soluble in water, where it forms a weak alkali.
The working
The formula NH3 has 1 nitrogen atom and 3 hydrogen atoms, 4 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 | 82.24% |
| Hydrogen (H) | 3 | 1.0080 | 3.024 | 17.76% |
14.007 + 3 × 1.0080 = 17.031 g/mol
With the rounded atomic masses used in many school books (N = 14, H = 1) the answer is 17 g/mol. The difference from 17.03 is too small to matter in most school sums.
Percentage composition
By mass, NH3 is 82.24% nitrogen and 17.76% hydrogen. The largest share comes from nitrogen. In a 100 g sample there are 82.2 g of nitrogen and 17.8 g of hydrogen.
Notice that hydrogen has more atoms in the formula (3) than nitrogen (1), yet gives a smaller share of the mass. Percentage by mass depends on how heavy each atom is, not only on how many there are.
Worked examples
Grams to moles. How many moles are in 5 g of NH3? Divide the mass by the molar mass: 5 ÷ 17.03 = 0.2936 mol.
Moles to grams. What is the mass of 0.25 mol of NH3? Multiply: 0.25 × 17.03 = 4.258 g.
Counting particles. 5 g contains 0.2936 mol × 6.022 × 1023 = 1.768 × 1023 molecules, and 7.072 × 1023 atoms in all.
Making a solution. A 0.1 mol/L solution contains 0.1 × 17.03 = 1.703 g of NH3 in each litre. For 250 mL, weigh 0.4258 g and make it up to the mark with water.
As a gas. At 0 °C and 1 atmosphere one mole of an ideal gas occupies 22.4 litres, so the density of NH3 is about 17.03 ÷ 22.4 = 0.76 g per litre. Air averages about 29 g/mol, so this gas is lighter than air.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 1.703 g |
| 0.5 mol | 8.515 g |
| 1 mol | 17.03 g |
| 2 mol | 34.06 g |
| 5 mol | 85.16 g |
| Mass | Moles |
|---|---|
| 1 g | 0.05872 mol |
| 10 g | 0.5872 mol |
| 100 g | 5.872 mol |
| 1 kg | 58.72 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of NH3?
The molar mass of ammonia (NH3) is 17.03 g/mol, or 17.031 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of NH3?
100 ÷ 17.03 = 5.872 mol.
What is the mass of one molecule of NH3?
Divide the molar mass by the Avogadro constant: 17.03 ÷ 6.022 × 1023 = 2.828 × 10-23 g.
What is the percentage of nitrogen in NH3?
Nitrogen makes up 82.24% of the mass of NH3: 1 × 14.007 ÷ 17.031 × 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.