Moles to grams for potassium permanganate is a multiplication by 158.03234 g/mol. A mole weighs 158.0323 g, 100 mmol weighs 15.8032 g, 10 mmol weighs 1.58032 g and a millimole is 158.032 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. Potassium permanganate is 39.0983 (K) + 54.938 (Mn) + 4 × 15.999 (O), which is 158.03234 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: 4 of the 6 atoms in a formula unit are oxygen, and they account for 63.996 g of the 158.0323 g, or 40.5% 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.
A strong oxidiser used in water treatment and titration. Its solutions are intensely purple and stain everything, and they slowly decompose in light. At 158.0323 g/mol it is heavier than 18 of the 34 salts covered here, and that ranking matters more than it looks: sodium sulfate has a molar mass of 142.0355 g/mol, so a gram of it contains 11.3% more formula units than a gram of potassium permanganate. Weigh by mass and you are not weighing equal amounts of substance.
Two practical things move the result. Purity below 100% means the weighed mass overstates how much compound you have — at 98% assay, 3.1606 g of every 158.0323 g is not the compound — and any water picked up from the air does the same. Both are systematic, so they shift every solution made from that jar in the same direction.
The formula
n- The amount of potassium permanganate you need, in moles
158.03234- The molar mass of potassium permanganate 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 158.03234 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 potassium permanganate in grams
5 mmol × 158.0323 g/mol = 0.790162 g, which is 790.162 mg. Doubling the amount doubles the mass to 1.58032 g, because the relationship is a plain proportion once the molar mass is fixed.
250 mmol of potassium permanganate in grams
250 mmol × 158.0323 g/mol = 39.5081 g, which is 39,508.1 mg. Doubling the amount doubles the mass to 79.0162 g, because the relationship is a plain proportion once the molar mass is fixed.
2 mol of potassium permanganate in grams
2 mol × 158.0323 g/mol = 316.065 g, which is 316,065 mg. Doubling the amount doubles the mass to 632.129 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 potassium permanganate (KMnO4)?
It is 158.03234 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 39.0983 (K) + 54.938 (Mn) + 4 × 15.999 (O). One mole of potassium permanganate therefore weighs 158.0323 g, and a gram of it is 6.3278 mmol.
What percentage of potassium permanganate is oxygen?
40.5% by mass. Each formula unit contains 4 oxygen atoms contributing 63.996 g of the 158.0323 g total, so 100 g of potassium permanganate contains 40.5 g of oxygen and a kilogram contains 404.96 g of it.
How many grams is one mole of potassium permanganate?
158.03234 g, by definition of the molar mass. Two moles is 316.0647 g and half a mole is 79.01617 g.
How many grams is 0.1 mol, and how many milligrams is 1 mmol?
0.1 mol of potassium permanganate is 15.8032 g. One millimole is 158.032 mg and one micromole is 158.032 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 1.58 mg of potassium permanganate, weigh 15.8 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, KMnO4, at 158.03234 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 potassium permanganate
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Oxygen (O) | 4 | 15.999 | 63.996 | 40.5% |
| Manganese (Mn) | 1 | 54.93804 | 54.93804 | 34.76% |
| Potassium (K) | 1 | 39.0983 | 39.0983 | 24.74% |
| Total — one mole of potassium permanganate | 158.03234 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 158.03234 g/mol.
| Wanted | Weigh (g) | Weigh (mg) | With 2% over (g) |
|---|---|---|---|
| 1 µmol | 0.000158032 | 0.158032 | 0.000161193 |
| 10 µmol | 0.00158032 | 1.58032 | 0.00161193 |
| 100 µmol | 0.0158032 | 15.8032 | 0.0161193 |
| 1 mmol | 0.158032 | 158.032 | 0.161193 |
| 10 mmol | 1.58032 | 1580.32 | 1.61193 |
| 50 mmol | 7.90162 | 7901.62 | 8.05965 |
| 100 mmol | 15.8032 | 15,803.2 | 16.1193 |
| 250 mmol | 39.5081 | 39,508.1 | 40.2982 |
| 500 mmol | 79.0162 | 79,016.2 | 80.5965 |
| 750 mmol | 118.524 | 118,524 | 120.895 |
| 1 mol | 158.032 | 158,032 | 161.193 |
| 2 mol | 316.065 | 316,065 | 322.386 |
| 5 mol | 790.162 | 790,162 | 805.965 |
| 10 mol | 1580.32 | 1580323.430000 | 1611.93 |
Weigh is the amount multiplied by 158.03234 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 |
|---|---|---|---|
| Monopotassium phosphate | KH2PO4 | 136.0841 | 7.3484 |
| Disodium phosphate | Na2HPO4 | 141.9573 | 7.0444 |
| Sodium sulfate | Na2SO4 | 142.0355 | 7.0405 |
| Potassium permanganate (this page) | KMnO4 | 158.0323 | 6.3278 |
| Copper(II) sulfate | CuSO4 | 159.602 | 6.2656 |
| Iron(III) chloride | FeCl3 | 162.195 | 6.1654 |
| Trisodium phosphate | Na3PO4 | 163.9391 | 6.0998 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.