Molar MassMolar mass of ammonium nitrate (NH4NO3)
The molar mass of ammonium nitrate, NH4NO3, is 80.04 g/mol. One mole of it, which is 6.022 × 1023 formula units, has a mass of 80.04 grams.
80.04 g/mol
2 × 14.007 + 4 × 1.0080 + 3 × 15.999 = 80.043 · 9 atoms in the formula
About ammonium nitrate
Ammonium nitrate is a fertiliser rich in nitrogen, because both the ammonium ion and the nitrate ion carry a nitrogen atom. It dissolves in water with strong cooling, which is used in instant cold packs.
The working
The formula NH4NO3 has 2 nitrogen atoms, 4 hydrogen atoms and 3 oxygen atoms, 9 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) | 2 | 14.007 | 28.014 | 35.00% |
| Hydrogen (H) | 4 | 1.0080 | 4.032 | 5.04% |
| Oxygen (O) | 3 | 15.999 | 47.997 | 59.96% |
2 × 14.007 + 4 × 1.0080 + 3 × 15.999 = 80.043 g/mol
With the rounded atomic masses used in many school books (N = 14, H = 1, O = 16) the answer is 80 g/mol. The difference from 80.04 is too small to matter in most school sums.
Percentage composition
By mass, NH4NO3 is 35.00% nitrogen, 5.04% hydrogen and 59.96% oxygen. The largest share comes from oxygen. In a 100 g sample there are 35.0 g of nitrogen, 5.0 g of hydrogen and 60.0 g of oxygen.
Notice that hydrogen has more atoms in the formula (4) than oxygen (3), 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 20 g of NH4NO3? Divide the mass by the molar mass: 20 ÷ 80.04 = 0.2499 mol.
Moles to grams. What is the mass of 0.5 mol of NH4NO3? Multiply: 0.5 × 80.04 = 40.02 g.
Counting particles. 20 g contains 0.2499 mol × 6.022 × 1023 = 1.505 × 1023 formula units.
Making a solution. A 0.1 mol/L solution contains 0.1 × 80.04 = 8.004 g of NH4NO3 in each litre. For 250 mL, weigh 2.001 g and make it up to the mark with water.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 8.004 g |
| 0.5 mol | 40.02 g |
| 1 mol | 80.04 g |
| 2 mol | 160.1 g |
| 5 mol | 400.2 g |
| Mass | Moles |
|---|---|
| 1 g | 0.01249 mol |
| 10 g | 0.1249 mol |
| 100 g | 1.249 mol |
| 1 kg | 12.49 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of NH4NO3?
The molar mass of ammonium nitrate (NH4NO3) is 80.04 g/mol, or 80.043 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of NH4NO3?
100 ÷ 80.04 = 1.249 mol.
What is the mass of one formula unit of NH4NO3?
Divide the molar mass by the Avogadro constant: 80.04 ÷ 6.022 × 1023 = 1.329 × 10-22 g.
What is the percentage of oxygen in NH4NO3?
Oxygen makes up 59.96% of the mass of NH4NO3: 3 × 15.999 ÷ 80.043 × 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.