Molar MassMolar mass of barium sulphate (BaSO4)
The molar mass of barium sulphate, BaSO4, is 233.39 g/mol. One mole of it, which is 6.022 × 1023 formula units, has a mass of 233.39 grams.
233.39 g/mol
137.33 + 32.06 + 4 × 15.999 = 233.386 · 6 atoms in the formula · also called barium sulfate, barite
About barium sulphate
Barium sulphate is a dense white solid that does not dissolve in water or acids. Its formation as a white precipitate is the test for sulphate ions, and in gravimetric analysis the weighed precipitate gives the amount of sulphate.
Other names: barium sulfate, barite.
The working
The formula BaSO4 has 1 barium atom, 1 sulphur 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 |
|---|---|---|---|---|
| Barium (Ba) | 1 | 137.33 | 137.330 | 58.84% |
| Sulphur (S) | 1 | 32.06 | 32.060 | 13.74% |
| Oxygen (O) | 4 | 15.999 | 63.996 | 27.42% |
137.33 + 32.06 + 4 × 15.999 = 233.386 g/mol
With the rounded atomic masses used in many school books (Ba = 137, S = 32, O = 16) the answer is 233 g/mol. The difference from 233.39 is too small to matter in most school sums.
Percentage composition
By mass, BaSO4 is 58.84% barium, 13.74% sulphur and 27.42% oxygen. The largest share comes from barium. In a 100 g sample there are 58.8 g of barium, 13.7 g of sulphur and 27.4 g of oxygen.
Worked examples
Grams to moles. How many moles are in 20 g of BaSO4? Divide the mass by the molar mass: 20 ÷ 233.39 = 0.08569 mol.
Moles to grams. What is the mass of 0.5 mol of BaSO4? Multiply: 0.5 × 233.39 = 116.7 g.
Counting particles. 20 g contains 0.08569 mol × 6.022 × 1023 = 5.161 × 1022 formula units.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 23.34 g |
| 0.5 mol | 116.7 g |
| 1 mol | 233.4 g |
| 2 mol | 466.8 g |
| 5 mol | 1167 g |
| Mass | Moles |
|---|---|
| 1 g | 0.004285 mol |
| 10 g | 0.04285 mol |
| 100 g | 0.4285 mol |
| 1 kg | 4.285 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of BaSO4?
The molar mass of barium sulphate (BaSO4) is 233.39 g/mol, or 233.386 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of BaSO4?
100 ÷ 233.39 = 0.4285 mol.
What is the mass of one formula unit of BaSO4?
Divide the molar mass by the Avogadro constant: 233.39 ÷ 6.022 × 1023 = 3.875 × 10-22 g.
What is the percentage of barium in BaSO4?
Barium makes up 58.84% of the mass of BaSO4: 1 × 137.33 ÷ 233.386 × 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.