Molar Mass of Calcium Carbonate
| Value | 0.100086 kg/mol |
| Status | Measured: ± 0.0000054 kg/mol (0.000054 relative) |
| Source | IUPAC |
| Categories | ChemistryWater Treatment |
| gram per mole | 100.086 g/mol |
| kilogram per kilomole | 100.086 kg/kmol |
| milligram per millimole | 100.086 mg/mmol |
| pound per pound-mole | 100.086 lb/lb-mol |
| dalton (as molar mass) | 100.086 Da |
| kilogram per mole | 0.100086 kg/mol |
| kilodalton (as molar mass) | 0.100086 kDa |
Learning zone
Calcium carbonate's convenient 100.086 g/mol, and its equivalent weight of almost exactly 50 g/eq, are the reason the entire water industry reports hardness and alkalinity "as CaCO₃" rather than in the ions actually present. A water with 80 mg/L of Ca²⁺ and 12 mg/L of Mg²⁺ is converted to a single number, 249 mg/L as CaCO₃, by scaling each ion by 50 divided by its own equivalent weight. It is a unit of convenience, not a claim that any calcium carbonate is dissolved.
The same compound is limestone, chalk, marble, eggshell and the scale that furs a kettle element. Because its solubility falls as temperature rises — the opposite of most salts — it precipitates preferentially on the hottest surface in a system, which is exactly the heat-exchanger tube you least want coated. The Langelier index exists to predict whether a given water will lay that scale down or dissolve it.