Equivalent Weight of Sulfuric Acid
| Value | 0.049036 kg/mol |
| Status | Measured: ± 0.00001 kg/mol (0.0002 relative) |
| Source | IUPAC |
| Categories | Chemistryequivalent-weightwater-treatment |
| gram per mole | 49.036 g/mol |
| kilogram per kilomole | 49.036 kg/kmol |
| milligram per millimole | 49.036 mg/mmol |
| pound per pound-mole | 49.036 lb/lb-mol |
| dalton (as molar mass) | 49.036 Da |
| kilogram per mole | 0.049036 kg/mol |
| kilodalton (as molar mass) | 0.049036 kDa |
Learning zone
Sulfuric acid is diprotic: both protons come off against alkalinity, so its equivalent weight is the molar mass divided by two — 98.072 / 2 = 49.036 g/eq — and its normality is always twice its molarity. The number every alkalinity-reduction calculation leans on follows directly: one equivalent of acid, 49.036 g, destroys one equivalent of alkalinity, which the water industry books as 50.04 g as CaCO₃. The ratio 49.036/50.04 = 0.98 is why the field arithmetic is so forgiving — a pound of pure H₂SO₄ takes out very nearly a pound of alkalinity as CaCO₃, before correcting for the strength of the commercial acid actually in the drum.
The classic dosing error is feeding the molar mass where the equivalent weight belongs, which oversizes the acid feed by exactly a factor of two — enough to crash a cooling tower's pH and strip its protective film in an afternoon. The other thing to carry from this page is what the acid leaves behind: every equivalent fed adds half a mole of sulfate, and in a high-cycles tower that sulfate walks the water toward the calcium sulfate solubility limit — the gypsum scale that, unlike carbonate, no acid will ever clean off.