Moles to grams for sodium hypochlorite is a multiplication by 74.438769 g/mol. A mole weighs 74.43877 g, 100 mmol weighs 7.44388 g, 10 mmol weighs 0.744388 g and a millimole is 74.4388 mg. Those four figures cover most of what gets weighed out in practice, and the table below extends them from a micromole up to ten moles.
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.
Two habits make the weighed mass match the calculation. Weigh into a container you have tared rather than onto paper, because what stays behind on paper is a real loss — on a 100 mg weighing it is easily a percent. And when the target is under about 20 mg, weigh ten times that and dilute, since the absolute error of the balance does not shrink with the sample.
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
n- The amount of sodium hypochlorite you need, in moles
74.438769- The molar mass of sodium hypochlorite in g/mol, derived from its formula
m- The mass to weigh out, in grams
How it works, step by step
- Enter the amount you need, in moles.
- It is multiplied by 74.438769 g/mol.
- The result is the mass to weigh out, also given in milligrams.
- Weigh into a tared container; anything left in the boat is a real loss from the amount you calculated.
Worked examples
5 mmol of sodium hypochlorite in grams
5 mmol × 74.43877 g/mol = 0.372194 g, which is 372.194 mg. Doubling the amount doubles the mass to 0.744388 g, because the relationship is a plain proportion once the molar mass is fixed.
250 mmol of sodium hypochlorite in grams
250 mmol × 74.43877 g/mol = 18.6097 g, which is 18,609.7 mg. Doubling the amount doubles the mass to 37.2194 g, because the relationship is a plain proportion once the molar mass is fixed.
2 mol of sodium hypochlorite in grams
2 mol × 74.43877 g/mol = 148.878 g, which is 148,878 mg. Doubling the amount doubles the mass to 297.755 g, because the relationship is a plain proportion once the molar mass is fixed.
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 grams is one mole of sodium hypochlorite?
74.438769 g, by definition of the molar mass. Two moles is 148.8775 g and half a mole is 37.21938 g.
How many grams is 0.1 mol, and how many milligrams is 1 mmol?
0.1 mol of sodium hypochlorite is 7.44388 g. One millimole is 74.4388 mg and one micromole is 74.4388 µg, which is the range most bench work sits in.
How do I weigh out an amount too small for my balance?
Weigh a larger mass and dilute it. To get 0.7444 mg of sodium hypochlorite, weigh 7.444 mg into 100 mL, then take 10 mL of that: the absolute error of the balance stays the same while the amount delivered falls by a factor of ten.
Should I use the hydrate or the anhydrous molar mass?
This page is the anhydrous form, NaClO, at 74.438769 g/mol. If your jar is the other form the molar mass differs and so will every mass you weigh, so check the label before using the figure. Salts that are sold as hydrates weigh more per mole because the water is part of the crystal.
Moles to grams reference for 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.
| Wanted | Weigh (g) | Weigh (mg) | With 2% over (g) |
|---|---|---|---|
| 1 µmol | 0.000074 | 0.0744388 | 0.000076 |
| 10 µmol | 0.000744388 | 0.744388 | 0.000759275 |
| 100 µmol | 0.00744388 | 7.44388 | 0.00759275 |
| 1 mmol | 0.0744388 | 74.4388 | 0.0759275 |
| 10 mmol | 0.744388 | 744.388 | 0.759275 |
| 50 mmol | 3.72194 | 3721.94 | 3.79638 |
| 100 mmol | 7.44388 | 7443.88 | 7.59275 |
| 250 mmol | 18.6097 | 18,609.7 | 18.9819 |
| 500 mmol | 37.2194 | 37,219.4 | 37.9638 |
| 750 mmol | 55.8291 | 55,829.1 | 56.9457 |
| 1 mol | 74.4388 | 74,438.8 | 75.9275 |
| 2 mol | 148.878 | 148,878 | 151.855 |
| 5 mol | 372.194 | 372,194 | 379.638 |
| 10 mol | 744.388 | 744,388 | 759.275 |
Weigh is the amount multiplied by 74.438769 g/mol. The last column carries a 2% allowance, which is what you take when some of the solid will be left in the weighing boat.
| 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.