The molar mass of sodium hypochlorite, NaClO, is 74.438769 g/mol. That single number is what connects a mass you can weigh to an amount of substance you can react: one mole is 74.43877 g, and a gram of it is 8.09e+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 hypochlorite is 22.9898 (Na) + 35.45 (Cl) + 15.999 (O), which is 74.438769 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Chlorine makes up the largest share of the mass: 1 of the 3 atoms in a formula unit is chlorine, and they account for 35.45 g of the 74.43877 g, or 47.62% 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 hypochlorite is 74.4388 mg and one micromole is 74.4388 µg, so a balance reading to a milligram places you within 13.43 µmol. A single formula unit weighs 1.2361e-22 g, which is why the count in the gauge runs into the sextillions for any mass you can see.
Household bleach, sold as a percentage of active chlorine. It decomposes steadily, so an old bottle is weaker than its label says. At 74.43877 g/mol it is heavier than 3 of the 34 salts covered here, and that ranking matters more than it looks: sodium nitrite has a molar mass of 68.99477 g/mol, so a gram of it contains 7.89% more formula units than a gram of sodium hypochlorite. 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 1.4888 g of a nominal 74.43877 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 hypochlorite in grams
74.438769- The molar mass of sodium hypochlorite 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 hypochlorite in grams.
- It is divided by the molar mass, 74.438769 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 hypochlorite as a molecule count
0.5 g divided by 74.43877 g/mol is 0.00671693 mol, and multiplying by the Avogadro constant gives 4.045e+21 formula units of sodium hypochlorite. The same mass is 6.7169 mmol, which is the figure a reaction is actually planned in.
5 g of sodium hypochlorite as a molecule count
5 g divided by 74.43877 g/mol is 0.0671693 mol, and multiplying by the Avogadro constant gives 4.045e+22 formula units of sodium hypochlorite. The same mass is 67.169 mmol, which is the figure a reaction is actually planned in.
50 g of sodium hypochlorite as a molecule count
50 g divided by 74.43877 g/mol is 0.671693 mol, and multiplying by the Avogadro constant gives 4.045e+23 formula units of sodium hypochlorite. The same mass is 671.69 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 hypochlorite (NaClO)?
It is 74.438769 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 22.9898 (Na) + 35.45 (Cl) + 15.999 (O). One mole of sodium hypochlorite therefore weighs 74.43877 g, and a gram of it is 13.434 mmol.
What percentage of sodium hypochlorite is chlorine?
47.62% by mass. Each formula unit contains 1 chlorine atom contributing 35.45 g of the 74.43877 g total, so 100 g of sodium hypochlorite contains 47.62 g of chlorine and a kilogram contains 476.23 g of it.
How many molecules are in one gram of sodium hypochlorite?
About 8.09e+21. One gram is 0.0134339 mol, and each mole contains 6.02214076 × 10²³ formula units by definition of the mole, so the count is that constant divided by 74.43877.
How much does a single molecule of sodium hypochlorite weigh?
1.2361e-22 g, which is 74.438769 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 hypochlorite it is 74.438769. Molar mass carries grams per mole: 74.438769 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. Chlorine is quoted as 35.45 rather than a whole number for that reason, and the same applies to the other elements here, which is why sodium hypochlorite comes out at 74.438769 g/mol rather than 74.
Molar mass, composition and mole equivalents of sodium hypochlorite
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Chlorine (Cl) | 1 | 35.45 | 35.45 | 47.62% |
| Sodium (Na) | 1 | 22.98977 | 22.98977 | 30.88% |
| Oxygen (O) | 1 | 15.999 | 15.999 | 21.49% |
| Total — one mole of sodium hypochlorite | 74.438769 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 74.438769 g/mol.
| Amount | Mass (g) | Mass (mg) | Formula units |
|---|---|---|---|
| 1 µmol | 0.000074 | 0.0744388 | 6.022e+17 |
| 10 µmol | 0.000744388 | 0.744388 | 6.022e+18 |
| 100 µmol | 0.00744388 | 7.44388 | 6.022e+19 |
| 1 mmol | 0.0744388 | 74.4388 | 6.022e+20 |
| 10 mmol | 0.744388 | 744.388 | 6.022e+21 |
| 50 mmol | 3.72194 | 3721.94 | 3.011e+22 |
| 100 mmol | 7.44388 | 7443.88 | 6.022e+22 |
| 250 mmol | 18.6097 | 18,609.7 | 1.506e+23 |
| 500 mmol | 37.2194 | 37,219.4 | 3.011e+23 |
| 750 mmol | 55.8291 | 55,829.1 | 4.517e+23 |
| 1 mol | 74.4388 | 74,438.8 | 6.022e+23 |
| 2 mol | 148.878 | 148,878 | 1.204e+24 |
| 5 mol | 372.194 | 372,194 | 3.011e+24 |
| 10 mol | 744.388 | 744,388 | 6.022e+24 |
Mass is the amount multiplied by 74.438769 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 |
|---|---|---|---|
| Ammonium chloride | NH4Cl | 53.489 | 18.695 |
| Sodium chloride | NaCl | 58.43977 | 17.112 |
| Sodium nitrite | NaNO2 | 68.99477 | 14.494 |
| Sodium hypochlorite (this page) | NaClO | 74.43877 | 13.434 |
| Potassium chloride | KCl | 74.5483 | 13.414 |
| Ammonium nitrate | NH4NO3 | 80.043 | 12.493 |
| Sodium bicarbonate | NaHCO3 | 84.00577 | 11.904 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.