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Molar mass of sulfuric acid

The molar mass of sulfuric acid (H₂SO₄) is 98.07 g/mol: the sum of the atomic weights 2 × 1.0080 + 32.06 + 4 × 15.999. School problems round it to 98 g/mol (H = 1, S = 32, O = 16).

H2SO4 sulfuric acid

Molar mass

98.07 g/mol

For school problems (H = 1, S = 32, O = 16): 98 g/mol

Breakdown by element

M(H2SO4) = 2 × 1.0080 + 32.06 + 4 × 15.999 = 98.07 g/mol

The result is rounded to the precision of the least precise atomic weight. Atomic weights from IUPAC (CIAAW). PubChem gives 98.08 g/mol: the last digit differs because the atomic weights are rounded differently. PubChem CID 1118

What is sulfuric acid?

Sulfuric acid is a heavy, oily, colourless and odourless liquid and a strong diprotic acid. It is one of the chemical industry’s most important products: it is used to make fertilisers and fills car batteries.

The concentrated acid greedily absorbs water and chars sugar, paper and wood. To dilute it, pour the acid into water, never the other way round: so much heat is released that the water can boil and spatter the acid.

Properties

State at 25 °C
Liquid
Density
1.8302 g/cm³ 25 °C
Melting point
10.31 °C
Boiling point
337 °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 sulfuric acid

For school problems (H = 1, S = 32, O = 16): M(H₂SO₄) = 98 g/mol

  1. Problem 1

    How many moles are in 392 g of H₂SO₄?

    n = m ÷ M = 392 g ÷ 98 g/mol

    Answer: 4 mol

  2. Problem 2

    What is the mass of 0.5 mol of H₂SO₄?

    m = n × M = 0.5 mol × 98 g/mol

    Answer: 49 g

  3. Problem 3

    What is the mass percentage of S in H₂SO₄?

    w(S) = M(S) ÷ M(H₂SO₄) = 32 ÷ 98 ≈ 0.327

    Answer: 32.7%

  4. Problem 4

    How many molecules are in 0.2 mol of H₂SO₄?

    N = n × NA = 0.2 mol × 6.02 × 10²³ mol⁻¹

    Answer: 1.204 × 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.