Molar MassMolar mass of potassium sulphate (K2SO4)
The molar mass of potassium sulphate, K2SO4, is 174.25 g/mol. One mole of it, which is 6.022 × 1023 formula units, has a mass of 174.25 grams.
174.25 g/mol
2 × 39.098 + 32.06 + 4 × 15.999 = 174.252 · 7 atoms in the formula · also called sulphate of potash
About potassium sulphate
Potassium sulphate is a fertiliser that supplies potassium without chloride, which suits crops such as tobacco and some fruits.
Other names: sulphate of potash.
The working
The formula K2SO4 has 2 potassium atoms, 1 sulphur atom and 4 oxygen atoms, 7 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) | 2 | 39.098 | 78.196 | 44.88% |
| Sulphur (S) | 1 | 32.06 | 32.060 | 18.40% |
| Oxygen (O) | 4 | 15.999 | 63.996 | 36.73% |
2 × 39.098 + 32.06 + 4 × 15.999 = 174.252 g/mol
With the rounded atomic masses used in many school books (K = 39, S = 32, O = 16) the answer is 174 g/mol. The difference from 174.25 is too small to matter in most school sums.
Percentage composition
By mass, K2SO4 is 44.88% potassium, 18.40% sulphur and 36.73% oxygen. The largest share comes from potassium. In a 100 g sample there are 44.9 g of potassium, 18.4 g of sulphur and 36.7 g of oxygen.
Worked examples
Grams to moles. How many moles are in 50 g of K2SO4? Divide the mass by the molar mass: 50 ÷ 174.25 = 0.2869 mol.
Moles to grams. What is the mass of 0.4 mol of K2SO4? Multiply: 0.4 × 174.25 = 69.7 g.
Counting particles. 50 g contains 0.2869 mol × 6.022 × 1023 = 1.728 × 1023 formula units.
Making a solution. A 0.1 mol/L solution contains 0.1 × 174.25 = 17.43 g of K2SO4 in each litre. For 250 mL, weigh 4.356 g and make it up to the mark with water.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 17.43 g |
| 0.5 mol | 87.13 g |
| 1 mol | 174.3 g |
| 2 mol | 348.5 g |
| 5 mol | 871.3 g |
| Mass | Moles |
|---|---|
| 1 g | 0.005739 mol |
| 10 g | 0.05739 mol |
| 100 g | 0.5739 mol |
| 1 kg | 5.739 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of K2SO4?
The molar mass of potassium sulphate (K2SO4) is 174.25 g/mol, or 174.252 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of K2SO4?
100 ÷ 174.25 = 0.5739 mol.
What is the mass of one formula unit of K2SO4?
Divide the molar mass by the Avogadro constant: 174.25 ÷ 6.022 × 1023 = 2.894 × 10-22 g.
What is the percentage of potassium in K2SO4?
Potassium makes up 44.88% of the mass of K2SO4: 2 × 39.098 ÷ 174.252 × 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.