Molar MassMolar mass of nitric acid (HNO3)
The molar mass of nitric acid, HNO3, is 63.01 g/mol. One mole of it, which is 6.022 × 1023 molecules, has a mass of 63.01 grams.
63.01 g/mol
1.0080 + 14.007 + 3 × 15.999 = 63.012 · 5 atoms in the formula · also called aqua fortis
About nitric acid
Nitric acid is a strong acid and a strong oxidising agent. It is made from ammonia by the Ostwald process and goes mainly into fertilisers such as ammonium nitrate and into explosives. It turns skin yellow, a reaction with protein that is used as a laboratory test.
Other names: aqua fortis.
The working
The formula HNO3 has 1 hydrogen atom, 1 nitrogen atom and 3 oxygen atoms, 5 atoms in all. Multiply each count by the atomic weight of the element and add:
| Element | Atoms | Atomic weight | Total | Share by mass |
|---|---|---|---|---|
| Hydrogen (H) | 1 | 1.0080 | 1.008 | 1.60% |
| Nitrogen (N) | 1 | 14.007 | 14.007 | 22.23% |
| Oxygen (O) | 3 | 15.999 | 47.997 | 76.17% |
1.0080 + 14.007 + 3 × 15.999 = 63.012 g/mol
With the rounded atomic masses used in many school books (H = 1, N = 14, O = 16) the answer is 63 g/mol. The difference from 63.01 is too small to matter in most school sums.
Percentage composition
By mass, HNO3 is 1.60% hydrogen, 22.23% nitrogen and 76.17% oxygen. The largest share comes from oxygen. In a 100 g sample there are 1.6 g of hydrogen, 22.2 g of nitrogen and 76.2 g of oxygen.
Worked examples
Grams to moles. How many moles are in 25 g of HNO3? Divide the mass by the molar mass: 25 ÷ 63.01 = 0.3967 mol.
Moles to grams. What is the mass of 0.1 mol of HNO3? Multiply: 0.1 × 63.01 = 6.301 g.
Counting particles. 25 g contains 0.3967 mol × 6.022 × 1023 = 2.389 × 1023 molecules, and 1.195 × 1024 atoms in all.
Making a solution. A 0.1 mol/L solution contains 0.1 × 63.01 = 6.301 g of HNO3 in each litre. For 250 mL, weigh 1.575 g and make it up to the mark with water.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 6.301 g |
| 0.5 mol | 31.51 g |
| 1 mol | 63.01 g |
| 2 mol | 126 g |
| 5 mol | 315.1 g |
| Mass | Moles |
|---|---|
| 1 g | 0.01587 mol |
| 10 g | 0.1587 mol |
| 100 g | 1.587 mol |
| 1 kg | 15.87 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of HNO3?
The molar mass of nitric acid (HNO3) is 63.01 g/mol, or 63.012 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of HNO3?
100 ÷ 63.01 = 1.587 mol.
What is the mass of one molecule of HNO3?
Divide the molar mass by the Avogadro constant: 63.01 ÷ 6.022 × 1023 = 1.046 × 10-22 g.
What is the percentage of oxygen in HNO3?
Oxygen makes up 76.17% of the mass of HNO3: 3 × 15.999 ÷ 63.012 × 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.