Molar MassMolar mass of barium chloride dihydrate (BaCl2·2H2O)
The molar mass of barium chloride dihydrate, BaCl2·2H2O, is 244.26 g/mol. One mole of it, which is 6.022 × 1023 formula units, has a mass of 244.26 grams.
244.26 g/mol
137.33 + 2 × 35.45 + 4 × 1.0080 + 2 × 15.999 = 244.260 · 9 atoms in the formula
About barium chloride dihydrate
Barium chloride crystals hold two water molecules. Their solution is the reagent used to test for sulphate ions.
The working
The formula BaCl2·2H2O has 1 barium atom, 2 chlorine atoms, 4 hydrogen atoms and 2 oxygen atoms, 9 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 | 56.22% |
| Chlorine (Cl) | 2 | 35.45 | 70.900 | 29.03% |
| Hydrogen (H) | 4 | 1.0080 | 4.032 | 1.65% |
| Oxygen (O) | 2 | 15.999 | 31.998 | 13.10% |
137.33 + 2 × 35.45 + 4 × 1.0080 + 2 × 15.999 = 244.260 g/mol
With the rounded atomic masses used in many school books (Ba = 137, Cl = 35.5, H = 1, O = 16) the answer is 244 g/mol. The difference from 244.26 is too small to matter in most school sums.
The water in the crystal
The part after the dot is water of crystallisation: 2 molecules of water for each BaCl2. That water has a mass of 2 × 18.015 = 36.03 g/mol, which is 14.8% of the crystal. Without it, the anhydrous part BaCl2 has a molar mass of 208.23 g/mol. Heating drives the water off, so a sample loses up to 14.8% of its mass. How this is used to find the number of waters is shown on the hydrates page.
Percentage composition
By mass, BaCl2·2H2O is 56.22% barium, 29.03% chlorine, 1.65% hydrogen and 13.10% oxygen. The largest share comes from barium. In a 100 g sample there are 56.2 g of barium, 29.0 g of chlorine, 1.7 g of hydrogen and 13.1 g of oxygen.
Notice that hydrogen has more atoms in the formula (4) than barium (1), yet gives a smaller share of the mass. Percentage by mass depends on how heavy each atom is, not only on how many there are.
Worked examples
Grams to moles. How many moles are in 250 g of BaCl2·2H2O? Divide the mass by the molar mass: 250 ÷ 244.26 = 1.023 mol.
Moles to grams. What is the mass of 0.2 mol of BaCl2·2H2O? Multiply: 0.2 × 244.26 = 48.85 g.
Counting particles. 250 g contains 1.023 mol × 6.022 × 1023 = 6.164 × 1023 formula units.
Making a solution. A 0.1 mol/L solution contains 0.1 × 244.26 = 24.43 g of BaCl2·2H2O in each litre. For 250 mL, weigh 6.107 g and make it up to the mark with water.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 24.43 g |
| 0.5 mol | 122.1 g |
| 1 mol | 244.3 g |
| 2 mol | 488.5 g |
| 5 mol | 1221 g |
| Mass | Moles |
|---|---|
| 1 g | 0.004094 mol |
| 10 g | 0.04094 mol |
| 100 g | 0.4094 mol |
| 1 kg | 4.094 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of BaCl2.2H2O?
The molar mass of barium chloride dihydrate (BaCl2.2H2O) is 244.26 g/mol, or 244.260 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of BaCl2.2H2O?
100 ÷ 244.26 = 0.4094 mol.
What is the mass of one formula unit of BaCl2.2H2O?
Divide the molar mass by the Avogadro constant: 244.26 ÷ 6.022 × 1023 = 4.056 × 10-22 g.
What is the percentage of barium in BaCl2.2H2O?
Barium makes up 56.22% of the mass of BaCl2.2H2O: 1 × 137.33 ÷ 244.260 × 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.