Equivalent Weight of Hydrochloric Acid
| Value | 0.036458 kg/mol |
| Status | Measured: ± 0.00001 kg/mol (0.00027 relative) |
| Source | IUPAC |
| Categories | Chemistryequivalent-weightwater-treatment |
| gram per mole | 36.458 g/mol |
| kilogram per kilomole | 36.458 kg/kmol |
| milligram per millimole | 36.458 mg/mmol |
| pound per pound-mole | 36.458 lb/lb-mol |
| dalton (as molar mass) | 36.458 Da |
| kilogram per mole | 0.036458 kg/mol |
| kilodalton (as molar mass) | 0.036458 kDa |
Learning zone
Hydrochloric acid is monoprotic, so there is no division to do: 1.008 + 35.45 = 36.458 g/mol, and one proton per molecule makes the equivalent weight the same number. Each 36.458 g of pure HCl removes one equivalent of alkalinity — 50.04 g as CaCO₃ — so gram for gram it hits about 37 % harder than sulfuric acid. What arrives on site is never pure: muriatic acid, the commercial grade, is typically 31.45 % HCl (20 °Baumé), and the acid-feed solver's strength input exists exactly for that correction.
Hydrochloric earns its place where sulfate is unwelcome — ahead of a reverse-osmosis membrane running near the gypsum limit, or in a closed loop where added sulfate would feed sulfate-reducing bacteria. Its own baggage is chloride: every equivalent fed adds a chloride ion, and chloride is the numerator of the Larson–Skold index, the aggressive species that pits mild steel. The choice between the two workhorse acids is usually a choice about which anion the system can better afford to accumulate.