The molar mass of sodium nitrate, NaNO3, is 84.993769 g/mol. That single number is what connects a mass you can weigh to an amount of substance you can react: one mole is 84.99377 g, and a gram of it is 7.085e+21 formula units. The calculator turns any weighed mass into that count, and reports the amount in moles, millimoles and the mass of a single formula unit alongside it.
The figure comes from the formula. Sodium nitrate is 22.9898 (Na) + 14.007 (N) + 3 × 15.999 (O), which is 84.993769 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Oxygen makes up the largest share of the mass: 3 of the 5 atoms in a formula unit are oxygen, and they account for 47.997 g of the 84.99377 g, or 56.47% by mass. The derivation table below breaks the whole molecule down element by element.
The numbers a bench actually uses sit at the millimole scale. One millimole of sodium nitrate is 84.9938 mg and one micromole is 84.9938 µg, so a balance reading to a milligram places you within 11.77 µmol. A single formula unit weighs 1.4114e-22 g, which is why the count in the gauge runs into the sextillions for any mass you can see.
Chile saltpetre, used as a fertiliser and a heat-transfer salt. It is hygroscopic, unlike the potassium salt, which is why curing mixes prefer KNO3. At 84.99377 g/mol it is heavier than 7 of the 34 salts covered here, and that ranking matters more than it looks: sodium bicarbonate has a molar mass of 84.00577 g/mol, so a gram of it contains 1.18% more formula units than a gram of sodium nitrate. Weigh by mass and you are not weighing equal amounts of substance.
Purity is the usual gap between the calculation and the balance. A reagent sold at 98% means 1.6999 g of a nominal 84.99377 g is something else, so for exact work you divide the weighed mass by the assay figure on the certificate. For most purposes the difference is smaller than the error in reading the meniscus, but it is systematic rather than random, so it does not average out.
The formula
m- The mass of sodium nitrate in grams
84.993769- The molar mass of sodium nitrate in g/mol, derived from its formula
N- The number of formula units that mass contains
How it works, step by step
- Enter a mass of sodium nitrate in grams.
- It is divided by the molar mass, 84.993769 g/mol, giving the amount in moles.
- That amount is multiplied by the Avogadro constant, 6.02214076 × 10²³ per mole, to give the number of formula units.
- The panel also reports the amount in moles and millimoles and the mass of one formula unit.
Worked examples
0.5 g of sodium nitrate as a molecule count
0.5 g divided by 84.99377 g/mol is 0.00588278 mol, and multiplying by the Avogadro constant gives 3.543e+21 formula units of sodium nitrate. The same mass is 5.8828 mmol, which is the figure a reaction is actually planned in.
5 g of sodium nitrate as a molecule count
5 g divided by 84.99377 g/mol is 0.0588278 mol, and multiplying by the Avogadro constant gives 3.543e+22 formula units of sodium nitrate. The same mass is 58.828 mmol, which is the figure a reaction is actually planned in.
50 g of sodium nitrate as a molecule count
50 g divided by 84.99377 g/mol is 0.588278 mol, and multiplying by the Avogadro constant gives 3.543e+23 formula units of sodium nitrate. The same mass is 588.28 mmol, which is the figure a reaction is actually planned in.
How to read your score
Frequently asked questions
What is the molar mass of sodium nitrate (NaNO3)?
It is 84.993769 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 22.9898 (Na) + 14.007 (N) + 3 × 15.999 (O). One mole of sodium nitrate therefore weighs 84.99377 g, and a gram of it is 11.766 mmol.
What percentage of sodium nitrate is oxygen?
56.47% by mass. Each formula unit contains 3 oxygen atoms contributing 47.997 g of the 84.99377 g total, so 100 g of sodium nitrate contains 56.47 g of oxygen and a kilogram contains 564.71 g of it.
How many molecules are in one gram of sodium nitrate?
About 7.085e+21. One gram is 0.0117656 mol, and each mole contains 6.02214076 × 10²³ formula units by definition of the mole, so the count is that constant divided by 84.99377.
How much does a single molecule of sodium nitrate weigh?
1.4114e-22 g, which is 84.993769 daltons. It is the molar mass divided by the Avogadro constant, and the number in daltons is numerically the same as the molar mass in g/mol — that equivalence is what makes the mole convenient.
Is molar mass the same as molecular weight?
They are the same number in ordinary use but not the same quantity. Molecular weight, properly relative molecular mass, is a ratio and has no unit: for sodium nitrate it is 84.993769. Molar mass carries grams per mole: 84.993769 g/mol. Because the mole is defined so those agree, you can read one off the other.
Why is the molar mass not a whole number?
Because standard atomic weights are averages over the isotopes found in nature. Oxygen is quoted as 15.999 rather than a whole number for that reason, and the same applies to the other elements here, which is why sodium nitrate comes out at 84.993769 g/mol rather than 85.
Molar mass, composition and mole equivalents of sodium nitrate
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Oxygen (O) | 3 | 15.999 | 47.997 | 56.47% |
| Sodium (Na) | 1 | 22.98977 | 22.98977 | 27.05% |
| Nitrogen (N) | 1 | 14.007 | 14.007 | 16.48% |
| Total — one mole of sodium nitrate | 84.993769 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 84.993769 g/mol.
| Amount | Mass (g) | Mass (mg) | Formula units |
|---|---|---|---|
| 1 µmol | 0.000085 | 0.0849938 | 6.022e+17 |
| 10 µmol | 0.000849938 | 0.849938 | 6.022e+18 |
| 100 µmol | 0.00849938 | 8.49938 | 6.022e+19 |
| 1 mmol | 0.0849938 | 84.9938 | 6.022e+20 |
| 10 mmol | 0.849938 | 849.938 | 6.022e+21 |
| 50 mmol | 4.24969 | 4249.69 | 3.011e+22 |
| 100 mmol | 8.49938 | 8499.38 | 6.022e+22 |
| 250 mmol | 21.2484 | 21,248.4 | 1.506e+23 |
| 500 mmol | 42.4969 | 42,496.9 | 3.011e+23 |
| 750 mmol | 63.7453 | 63,745.3 | 4.517e+23 |
| 1 mol | 84.9938 | 84,993.8 | 6.022e+23 |
| 2 mol | 169.988 | 169,988 | 1.204e+24 |
| 5 mol | 424.969 | 424,969 | 3.011e+24 |
| 10 mol | 849.938 | 849,938 | 6.022e+24 |
Mass is the amount multiplied by 84.993769 g/mol. The last column is that amount multiplied by the Avogadro constant, 6.02214076 × 10²³ per mole.
| Compound | Formula | Molar mass (g/mol) | Millimoles in 1 g |
|---|---|---|---|
| Potassium chloride | KCl | 74.5483 | 13.414 |
| Ammonium nitrate | NH4NO3 | 80.043 | 12.493 |
| Sodium bicarbonate | NaHCO3 | 84.00577 | 11.904 |
| Sodium nitrate (this page) | NaNO3 | 84.99377 | 11.766 |
| Magnesium chloride | MgCl2 | 95.205 | 10.504 |
| Calcium carbonate | CaCO3 | 100.086 | 9.9914 |
| Potassium nitrate | KNO3 | 101.1023 | 9.891 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.