The molar mass of silicon dioxide (SiO2) is 60.083 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 |
|---|---|---|---|---|
| Oxygen (O) | 2 | 15.999 | 31.998 | 53.26% |
| Silicon (Si) | 1 | 28.085 | 28.085 | 46.74% |
| Total | 3 | 60.083 | 100.00% |
31.998 + 28.085 = 60.083 g/mol
Grams and moles
25 g of silicon dioxide is 0.4161 mol, because 25 ÷ 60.083 = 0.4161.
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: oxygen is 15.999, and really lies between 15.99903 and 15.99977; silicon is 28.085, and really lies between 28.084 and 28.086.
Silicon dioxide is 60.083 g/mol, split 53.26% oxygen and 46.74% silicon. It is quartz, sand, flint and the bulk of the Earth’s crust.
The formula is misleading in the same way NaCl is. There are no SiO2 molecules in a grain of sand. Each silicon sits at the centre of a tetrahedron of four oxygens, and each of those oxygens is shared with a neighbouring tetrahedron, so the ratio works out to one silicon per two oxygens across a network that extends through the entire crystal. The formula is a ratio in an infinite lattice, and this molar mass is a formula mass.
Compare it with carbon dioxide, the oxide of the element directly above silicon. Carbon dioxide is a gas of discrete molecules at 44.009 g/mol; silicon dioxide melts above 1,700 degrees Celsius. Same group, same formula pattern, and the difference is entirely in whether the element forms double bonds to oxygen or a continuous network.