Molar MassMolar mass of potassium permanganate (KMnO4)
The molar mass of potassium permanganate, KMnO4, is 158.03 g/mol. One mole of it, which is 6.022 × 1023 formula units, has a mass of 158.03 grams.
158.03 g/mol
39.098 + 54.938 + 4 × 15.999 = 158.032 · 6 atoms in the formula · also called potassium manganate(VII)
About potassium permanganate
Potassium permanganate forms dark purple crystals and gives an intensely purple solution. It is a strong oxidising agent used in redox titrations, where it acts as its own indicator, and as a disinfectant.
Other names: potassium manganate(VII).
The working
The formula KMnO4 has 1 potassium atom, 1 manganese atom and 4 oxygen atoms, 6 atoms in all. Multiply each count by the atomic weight of the element and add:
| Element | Atoms | Atomic weight | Total | Share by mass |
|---|---|---|---|---|
| Potassium (K) | 1 | 39.098 | 39.098 | 24.74% |
| Manganese (Mn) | 1 | 54.938 | 54.938 | 34.76% |
| Oxygen (O) | 4 | 15.999 | 63.996 | 40.50% |
39.098 + 54.938 + 4 × 15.999 = 158.032 g/mol
With the rounded atomic masses used in many school books (K = 39, Mn = 55, O = 16) the answer is 158 g/mol. The difference from 158.03 is too small to matter in most school sums.
Percentage composition
By mass, KMnO4 is 24.74% potassium, 34.76% manganese and 40.50% oxygen. The largest share comes from oxygen. In a 100 g sample there are 24.7 g of potassium, 34.8 g of manganese and 40.5 g of oxygen.
Worked examples
Grams to moles. How many moles are in 50 g of KMnO4? Divide the mass by the molar mass: 50 ÷ 158.03 = 0.3164 mol.
Moles to grams. What is the mass of 0.4 mol of KMnO4? Multiply: 0.4 × 158.03 = 63.21 g.
Counting particles. 50 g contains 0.3164 mol × 6.022 × 1023 = 1.905 × 1023 formula units.
Making a solution. A 0.1 mol/L solution contains 0.1 × 158.03 = 15.8 g of KMnO4 in each litre. For 250 mL, weigh 3.951 g and make it up to the mark with water.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 15.8 g |
| 0.5 mol | 79.02 g |
| 1 mol | 158 g |
| 2 mol | 316.1 g |
| 5 mol | 790.2 g |
| Mass | Moles |
|---|---|
| 1 g | 0.006328 mol |
| 10 g | 0.06328 mol |
| 100 g | 0.6328 mol |
| 1 kg | 6.328 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of KMnO4?
The molar mass of potassium permanganate (KMnO4) is 158.03 g/mol, or 158.032 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of KMnO4?
100 ÷ 158.03 = 0.6328 mol.
What is the mass of one formula unit of KMnO4?
Divide the molar mass by the Avogadro constant: 158.03 ÷ 6.022 × 1023 = 2.624 × 10-22 g.
What is the percentage of oxygen in KMnO4?
Oxygen makes up 40.50% of the mass of KMnO4: 4 × 15.999 ÷ 158.032 × 100.
Which values? This site uses the abridged standard atomic weights published by IUPAC (CIAAW), read on 12 November 2026. Your textbook or question paper may round them differently, for example H = 1 and O = 16, so its answer can differ slightly. In an exam, use the values the paper gives.