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Molar mass of nitric acid

The molar mass of nitric acid (HNO₃) is 63.012 g/mol: the sum of the atomic weights 1.0080 + 14.007 + 3 × 15.999. School problems round it to 63 g/mol (H = 1, N = 14, O = 16).

HNO3 nitric acid

Molar mass

63.012 g/mol

For school problems (H = 1, N = 14, O = 16): 63 g/mol

Breakdown by element

M(HNO3) = 1.0080 + 14.007 + 3 × 15.999 = 63.012 g/mol

The result is rounded to the precision of the least precise atomic weight. Atomic weights from IUPAC (CIAAW). PubChem gives 63.013 g/mol: the last digit differs because the atomic weights are rounded differently. PubChem CID 944

What is nitric acid?

Nitric acid is a colourless liquid, a strong acid and a strong oxidising agent. When stored or exposed to light it turns yellow: it partly decomposes, giving off brown NO₂ gas.

It reacts with almost all metals except gold and platinum, but as a rule no hydrogen is released. Concentrated nitric acid does not dissolve iron, aluminium and chromium: it covers them with a thin protective oxide film (passivation). Nitric acid is used to make fertilisers (nitrates) and explosives.

Properties

State at 25 °C
Liquid
Density
1.51 g/cm³ 20 °C
Melting point
−42 °C
Boiling point
83 °C
Solubility in water
mixes with water in any proportion

Sources: PubChem (HSDB, NIOSH), Wikipedia (CRC Handbook), NIST Chemistry WebBook; each value agrees in two of them.

Molar mass problems with nitric acid

For school problems (H = 1, N = 14, O = 16): M(HNO₃) = 63 g/mol

  1. Problem 1

    How many moles are in 94.5 g of HNO₃?

    n = m ÷ M = 94.5 g ÷ 63 g/mol

    Answer: 1.5 mol

  2. Problem 2

    What is the mass of 0.1 mol of HNO₃?

    m = n × M = 0.1 mol × 63 g/mol

    Answer: 6.3 g

  3. Problem 3

    What is the mass percentage of N in HNO₃?

    w(N) = M(N) ÷ M(HNO₃) = 14 ÷ 63 ≈ 0.222

    Answer: 22.2%

  4. Problem 4

    How many molecules are in 0.5 mol of HNO₃?

    N = n × NA = 0.5 mol × 6.02 × 10²³ mol⁻¹

    Answer: 3.01 × 10²³

What is molar mass?

Molar mass M is the mass of one mole of a substance, about 6.022 × 10²³ of its particles. It is measured in grams per mole (g/mol).

To find it, add up the atomic weights of all the atoms in the formula: multiply each element’s atomic weight by its subscript, the number of its atoms. In g/mol, the molar mass equals the relative molecular mass Mr.

For water: M(H₂O) = 2 × 1.0080 + 15.999 = 18.015 g/mol.