Equivalent Weight of Citric Acid
| Value | 0.064041 kg/mol |
| Status | Measured: ± 0.000005 kg/mol (0.000078 relative) |
| Source | IUPAC |
| Categories | Chemistryequivalent-weightwater-treatment |
| gram per mole | 64.041 g/mol |
| kilogram per kilomole | 64.041 kg/kmol |
| milligram per millimole | 64.041 mg/mmol |
| pound per pound-mole | 64.041 lb/lb-mol |
| dalton (as molar mass) | 64.041 Da |
| kilogram per mole | 0.064041 kg/mol |
| kilodalton (as molar mass) | 0.064041 kDa |
Learning zone
Citric acid carries three carboxylic acid groups, and the standard convention counts all of them: 192.123 / 3 = 64.041 g/eq. The three pKa values — 3.13, 4.76, 6.40 — sit close together and all below neutral, so against a base taken to completion the ÷3 figure is the honest one, and it is the number normality tables and citric-based cleaner formulations are built on. Be aware of what it means at the alkalinity endpoint, though: at pH 4.5 the third proton (and part of the second) has not yet titrated, so citric delivers somewhat less than three equivalents there and the ÷3 arithmetic slightly overstates its alkalinity-reduction punch.
Nobody chooses citric acid for bulk pH control anyway — per equivalent it costs multiples of sulfuric. It is chosen because the citrate left behind is a chelant: it holds iron and calcium in solution, which is why citric is the standard passivation and iron-removal cleaner for stainless systems and membranes, safe on metals that hydrochloric would pit. The molar mass here is the anhydrous acid; the monohydrate common in food-grade supply runs 210.14 g/mol, so a solution made from it delivers about 9 % fewer equivalents per kilogram weighed.