The molar mass of sodium carbonate (Na2CO3) is 105.988 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 | 11.33% |
| Sodium (Na) | 2 | 22.98976928 | 45.980 | 43.38% |
| Oxygen (O) | 3 | 15.999 | 47.997 | 45.29% |
| Total | 6 | 105.988 | 100.00% |
12.011 + 45.980 + 47.997 = 105.988 g/mol
Grams and moles
25 g of sodium carbonate is 0.2359 mol, because 25 ÷ 105.988 = 0.2359.
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.
Sodium carbonate is 105.988 g/mol: two sodiums at 45.980, one carbon at 12.011 and three oxygens at 47.997. Sodium makes up 43.38% of the mass.
Anhydrous soda ash is what that figure describes. Washing soda is the decahydrate, the same compound carrying ten waters of crystallisation at 286.138 g/mol, and 63% of that is water. The two are sold under names that do not distinguish them clearly, and confusing them is a factor-of-2.7 error in any calculation.
The compound is one of the oldest industrial chemicals, and glassmaking is still its largest use: adding it to silica lowers the melting point far enough to work sand into glass with an ordinary furnace.
In water it gives a distinctly alkaline solution despite containing no hydroxide, because the carbonate ion pulls protons from water. That is the standard demonstration of a salt of a weak acid behaving as a base.