Molar MassMolar mass of potassium chlorate (KClO3)
The molar mass of potassium chlorate, KClO3, is 122.55 g/mol. One mole of it, which is 6.022 × 1023 formula units, has a mass of 122.55 grams.
About potassium chlorate
Potassium chlorate gives off oxygen when heated, faster with manganese dioxide as a catalyst. This is the usual laboratory preparation of oxygen and a common source of mole questions. It is used in matches.
The working
The formula KClO3 has 1 potassium atom, 1 chlorine atom and 3 oxygen atoms, 5 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 | 31.91% |
| Chlorine (Cl) | 1 | 35.45 | 35.450 | 28.93% |
| Oxygen (O) | 3 | 15.999 | 47.997 | 39.17% |
39.098 + 35.45 + 3 × 15.999 = 122.545 g/mol
With the rounded atomic masses used in many school books (K = 39, Cl = 35.5, O = 16) the answer is 122.5 g/mol. The difference from 122.55 is too small to matter in most school sums.
Percentage composition
By mass, KClO3 is 31.91% potassium, 28.93% chlorine and 39.17% oxygen. The largest share comes from oxygen. In a 100 g sample there are 31.9 g of potassium, 28.9 g of chlorine and 39.2 g of oxygen.
Worked examples
Grams to moles. How many moles are in 5 g of KClO3? Divide the mass by the molar mass: 5 ÷ 122.55 = 0.0408 mol.
Moles to grams. What is the mass of 0.25 mol of KClO3? Multiply: 0.25 × 122.55 = 30.64 g.
Counting particles. 5 g contains 0.0408 mol × 6.022 × 1023 = 2.457 × 1022 formula units.
Making a solution. A 0.1 mol/L solution contains 0.1 × 122.55 = 12.25 g of KClO3 in each litre. For 250 mL, weigh 3.064 g and make it up to the mark with water.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 12.25 g |
| 0.5 mol | 61.27 g |
| 1 mol | 122.5 g |
| 2 mol | 245.1 g |
| 5 mol | 612.7 g |
| Mass | Moles |
|---|---|
| 1 g | 0.00816 mol |
| 10 g | 0.0816 mol |
| 100 g | 0.816 mol |
| 1 kg | 8.16 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of KClO3?
The molar mass of potassium chlorate (KClO3) is 122.55 g/mol, or 122.545 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of KClO3?
100 ÷ 122.55 = 0.816 mol.
What is the mass of one formula unit of KClO3?
Divide the molar mass by the Avogadro constant: 122.55 ÷ 6.022 × 1023 = 2.035 × 10-22 g.
What is the percentage of oxygen in KClO3?
Oxygen makes up 39.17% of the mass of KClO3: 3 × 15.999 ÷ 122.545 × 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.