The molar mass of potassium nitrate (KNO3) is 101.102 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 |
|---|---|---|---|---|
| Potassium (K) | 1 | 39.0983 | 39.098 | 38.67% |
| Nitrogen (N) | 1 | 14.007 | 14.007 | 13.86% |
| Oxygen (O) | 3 | 15.999 | 47.997 | 47.47% |
| Total | 5 | 101.102 | 100.00% |
39.098 + 14.007 + 47.997 = 101.102 g/mol
Grams and moles
25 g of potassium nitrate is 0.2473 mol, because 25 ÷ 101.102 = 0.2473.
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: nitrogen is 14.007, and really lies between 14.00643 and 14.00728; oxygen is 15.999, and really lies between 15.99903 and 15.99977.
Potassium nitrate is 101.102 g/mol. Potassium contributes 38.67%, the three oxygens 47.47% and nitrogen 13.86%.
Under the old name saltpetre it supplied the oxygen in gunpowder for six hundred years. Charcoal and sulfur cannot burn fast enough on air alone, and the nitrate carries oxygen within the solid itself. Nearly half the mass of the compound is that oxygen, which is what makes the mixture deflagrate rather than merely burn.
It is also a fertiliser, sold as 13-0-46, and those two numbers are simply the nitrogen and potassium percentages. The potassium figure is quoted as potassium oxide equivalent by convention rather than as the element, which is why 46 appears rather than 38.67. Fertiliser labelling has carried that convention since the nineteenth century and it catches out anyone reading it as straight elemental percentages.
Its solubility rises steeply with temperature, which makes it a favourite for recrystallisation experiments.