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Molar mass of hydrochloric acid

The molar mass of hydrochloric acid (HCl) is 36.46 g/mol: the sum of the atomic weights 1.0080 + 35.45. School problems round it to 36.5 g/mol (H = 1, Cl = 35.5).

HCl hydrochloric acid

Hydrochloric acid is a solution of hydrogen chloride (HCl) in water; the molar mass is that of HCl.

Molar mass

36.46 g/mol

For school problems (H = 1, Cl = 35.5): 36.5 g/mol

Breakdown by element

M(HCl) = 1.0080 + 35.45 = 36.46 g/mol

The result is rounded to the precision of the least precise atomic weight. Atomic weights from IUPAC (CIAAW). Agrees with PubChem: 36.46 g/mol. PubChem CID 313

What is hydrochloric acid?

Hydrochloric acid is a solution of hydrogen chloride in water and a strong monoprotic acid. The concentrated acid (36–38%) fumes in air: hydrogen chloride escapes from the solution and forms a mist with the moisture in the air.

Hydrochloric acid is found in gastric juice, where it helps digest food. In the lab it is used to make hydrogen from zinc, and carbonates are recognised because they fizz with it, giving off CO₂.

Properties

Properties of hydrogen chloride, HCl, the gas whose solution in water is hydrochloric acid. The acid’s own density and temperatures depend on its concentration.

State at 25 °C
Gas
Density
1.49 g/L 25 °C
Melting point
−114.22 °C
Boiling point
−85.05 °C
Solubility in water
soluble 82.3 g per 100 g of water, 0 °C

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

Molar mass problems with hydrochloric acid

For school problems (H = 1, Cl = 35.5): M(HCl) = 36.5 g/mol

  1. Problem 1

    How many moles are in 146 g of HCl?

    n = m ÷ M = 146 g ÷ 36.5 g/mol

    Answer: 4 mol

  2. Problem 2

    What is the mass of 3 mol of HCl?

    m = n × M = 3 mol × 36.5 g/mol

    Answer: 109.5 g

  3. Problem 3

    What is the mass percentage of Cl in HCl?

    w(Cl) = M(Cl) ÷ M(HCl) = 35.5 ÷ 36.5 ≈ 0.973

    Answer: 97.3%

  4. Problem 4

    How many molecules are in 0.2 mol of HCl?

    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.