Molar MassMolar mass of hydrogen chloride (HCl)
The molar mass of hydrogen chloride, HCl, is 36.46 g/mol. One mole of it, which is 6.022 × 1023 molecules, has a mass of 36.46 grams.
36.46 g/mol
1.0080 + 35.45 = 36.458 · 2 atoms in the formula · also called hydrochloric acid, muriatic acid
About hydrogen chloride
Hydrogen chloride is a colourless, sharp-smelling gas. Dissolved in water it becomes hydrochloric acid, the acid found in the stomach and the usual acid in school titrations. The figure on this page is for HCl itself; bottled acid is a solution in water, so its strength is given separately as a molarity.
Other names: hydrochloric acid, muriatic acid.
The working
The formula HCl has 1 hydrogen atom and 1 chlorine atom, 2 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 | 2.76% |
| Chlorine (Cl) | 1 | 35.45 | 35.450 | 97.24% |
1.0080 + 35.45 = 36.458 g/mol
With the rounded atomic masses used in many school books (H = 1, Cl = 35.5) the answer is 36.5 g/mol. The difference from 36.46 is too small to matter in most school sums.
Percentage composition
By mass, HCl is 2.76% hydrogen and 97.24% chlorine. The largest share comes from chlorine. In a 100 g sample there are 2.8 g of hydrogen and 97.2 g of chlorine.
Worked examples
Grams to moles. How many moles are in 5 g of HCl? Divide the mass by the molar mass: 5 ÷ 36.46 = 0.1371 mol.
Moles to grams. What is the mass of 0.25 mol of HCl? Multiply: 0.25 × 36.46 = 9.115 g.
Counting particles. 5 g contains 0.1371 mol × 6.022 × 1023 = 8.259 × 1022 molecules, and 1.652 × 1023 atoms in all.
Making a solution. A 0.1 mol/L solution contains 0.1 × 36.46 = 3.646 g of HCl in each litre. For 250 mL, weigh 0.9115 g and make it up to the mark with water.
As a gas. At 0 °C and 1 atmosphere one mole of an ideal gas occupies 22.4 litres, so the density of HCl is about 36.46 ÷ 22.4 = 1.63 g per litre. Air averages about 29 g/mol, so this gas is heavier than air.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 3.646 g |
| 0.5 mol | 18.23 g |
| 1 mol | 36.46 g |
| 2 mol | 72.92 g |
| 5 mol | 182.3 g |
| Mass | Moles |
|---|---|
| 1 g | 0.02743 mol |
| 10 g | 0.2743 mol |
| 100 g | 2.743 mol |
| 1 kg | 27.43 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of HCl?
The molar mass of hydrogen chloride (HCl) is 36.46 g/mol, or 36.458 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of HCl?
100 ÷ 36.46 = 2.743 mol.
What is the mass of one molecule of HCl?
Divide the molar mass by the Avogadro constant: 36.46 ÷ 6.022 × 1023 = 6.054 × 10-23 g.
What is the percentage of chlorine in HCl?
Chlorine makes up 97.24% of the mass of HCl: 1 × 35.45 ÷ 36.458 × 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.