Hydrochloric acid

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Hydrochloric acid, abbreviation HCl(aq), is a common acid both in the body and in the lab. It is, for example, a major component of gastric acid (pH 1-2, 0.5% w/v HCl). In experiments, it is used among other things to set the pH in buffers (e.g. Tris) and to reveal antigens (e.g. BrdU). Chemically speaking, it is a solution of the gas hydrogen chloride = HCl(g) in water.

Conversion % HCl to M HCl

chemical/physical data

  • 37% w/w HClaq has a density of 1.19 kg/L [1][2]
  • molecular weight of HCl = 36.5 g/mol [3][4]

% to molar conversion

  •  % w/w HCl to w/v HCl: 37% HCl x 1.9 kg/L density = 0.44 kg/L HCl
  • w/v to mol/v: 0.44 kg/L / 36.5 g/mol = 12 mol/L

Thus, fuming/concentrated HCl 37% is 12 molar (= M = mol/L).

diluted HCl from concentrated HCl

  • 1M HCl: add 1mol/12M = 83 ml conc. HCl to 1L of water or 8.3ml to 100ml
  • 2M HCl: add 2mol/12M = 167 ml conc. HCl to 1L of water or 16.7ml to 100ml

(other calculation start out with 37.5% and arrive at 82ml for 1M HCl [5])


  • Concentrated HCl is a very strong acid that will burn your skin instantly upon contact! Wear gloves, goggles, and lab coat.
  • Do not make the mistake of adding water to concentrated HCl. It has to acid into water. If you do it the wrong way the first drops of water mixing with the concentrated acid will heat up, evaporate, and can send drops of acid flying out of the container onto you.
  • HClaq above 25% w/w ~ 8M is corrosive and HClaq above 10% ~ 3M is irritant

See also

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