The molar mass of hydrochloric acid (HCl) is 36.458 g/mol.
Case matters: CO is carbon monoxide, Co is
cobalt. Brackets and hydrates are fine — try
or
.
| Element | Atoms | Atomic mass | Mass contributed | Percent |
|---|---|---|---|---|
| Chlorine (Cl) | 1 | 35.45 | 35.450 | 97.24% |
| Hydrogen (H) | 1 | 1.0080 | 1.008 | 2.76% |
| Total | 2 | 36.458 | 100.00% |
35.450 + 1.008 = 36.458 g/mol
Grams and moles
25 g of hydrochloric acid is 0.6857 mol, because 25 ÷ 36.458 = 0.6857.
These elements have no single atomic weight. Their isotopic mix varies slightly depending on where on Earth the sample came from, so the figure used here is the conventional value IUPAC publishes for when one number is needed: chlorine is 35.45, and really lies between 35.446 and 35.457; hydrogen is 1.0080, and really lies between 1.00784 and 1.00811.
Hydrogen chloride is 36.458 g/mol, and the breakdown is lopsided in a way worth noticing: chlorine carries 97.24% of the mass, the hydrogen only 2.76%. The entire acidic behaviour of the compound rests on that 1.008 grams per mole.
Pure HCl is a gas. Hydrochloric acid is that gas dissolved in water, and concentrated laboratory acid is about 37% HCl by mass with a density near 1.18 g/mL, which works out to roughly 12 moles per litre. Diluting to 1 M means about 83 mL of the concentrate made up to a litre, and the acid goes into the water rather than the other way round.
It is monoprotic, releasing one proton per molecule, so a mole neutralises exactly one mole of sodium hydroxide. That keeps the arithmetic simpler than sulfuric acid, where two protons per molecule mean equal masses of the two acids do not neutralise equal amounts of base.