The molar mass of sodium chloride (NaCl) is 58.440 g/mol.
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| Element | Atoms | Atomic mass | Mass contributed | Percent |
|---|---|---|---|---|
| Chlorine (Cl) | 1 | 35.45 | 35.450 | 60.66% |
| Sodium (Na) | 1 | 22.98976928 | 22.990 | 39.34% |
| Total | 2 | 58.440 | 100.00% |
35.450 + 22.990 = 58.440 g/mol
Grams and moles
25 g of sodium chloride is 0.4278 mol, because 25 ÷ 58.440 = 0.4278.
This element has 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: chlorine is 35.45, and really lies between 35.446 and 35.457.
Solid table salt contains no NaCl molecules at all. It is a cubic lattice in which every sodium ion is surrounded by six chloride ions and every chloride by six sodiums, repeating as far as the crystal goes. The formula records a ratio, and there is no particle anywhere in the solid that it describes.
So 58.440 g/mol is properly a formula mass rather than a molecular mass. Chlorine supplies 35.450 of it and sodium 22.990, which means chloride carries 60.66% of the weight of salt even though the two ions are present in equal numbers.
The figure doubles as a lab sanity check. A level teaspoon of salt is roughly 6 grams, a little over a tenth of a mole, or around 6 x 1022 ion pairs.