The molar mass of calcium carbonate (CaCO3) is 100.086 g/mol.
Case matters: CO is carbon monoxide, Co is
cobalt. Brackets and hydrates are fine — try
or
.
| Element | Atoms | Atomic mass | Mass contributed | Percent |
|---|---|---|---|---|
| Carbon (C) | 1 | 12.011 | 12.011 | 12.00% |
| Calcium (Ca) | 1 | 40.078 | 40.078 | 40.04% |
| Oxygen (O) | 3 | 15.999 | 47.997 | 47.96% |
| Total | 5 | 100.086 | 100.00% |
12.011 + 40.078 + 47.997 = 100.086 g/mol
Grams and moles
25 g of calcium carbonate is 0.2498 mol, because 25 ÷ 100.086 = 0.2498.
These elements have no single atomic weight. Their isotopic mix varies slightly depending on where on Earth the sample came from, so the figure used here is the conventional value IUPAC publishes for when one number is needed: carbon is 12.011, and really lies between 12.0096 and 12.0116; oxygen is 15.999, and really lies between 15.99903 and 15.99977.
Calcium carbonate is limestone, chalk, marble, eggshell and the shells of most marine life. At 100.086 g/mol it sits close enough to a round hundred to be genuinely useful for mental arithmetic: one gram of pure limestone is almost exactly one hundredth of a mole.
Calcium contributes 40.078 of that, carbon 12.011, and the three oxygens 47.997, making the compound 40.04% calcium by mass. Supplement labelling turns on this. A 1,250 mg calcium carbonate tablet delivers about 500 mg of elemental calcium, and the dose printed on the front of the bottle is usually the second number.
Heat it and carbon dioxide is driven off, leaving calcium oxide at 56.077 g/mol. The 44.009 g/mol difference is exactly the molar mass of the CO2 that left. That reaction is calcination, it is how cement is made, and the carbon dioxide it releases is a large share of global industrial emissions before any fuel is burned to drive it.