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Molar mass of calcium chloride dihydrate (CaCl2·2H2O)

The molar mass of calcium chloride dihydrate, CaCl2·2H2O, is 147.01 g/mol. One mole of it, which is 6.022 × 1023 formula units, has a mass of 147.01 grams.

147.01 g/mol

40.078 + 2 × 35.45 + 4 × 1.0080 + 2 × 15.999 = 147.008 · 9 atoms in the formula

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About calcium chloride dihydrate

This is a common commercial form of calcium chloride. Check the label when making up a solution, because the anhydrous salt and the hydrates need different masses.

The working

The formula CaCl2·2H2O has 1 calcium 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:

ElementAtomsAtomic weightTotalShare by mass
Calcium (Ca)140.07840.07827.26%
Chlorine (Cl)235.4570.90048.23%
Hydrogen (H)41.00804.0322.74%
Oxygen (O)215.99931.99821.77%

40.078 + 2 × 35.45 + 4 × 1.0080 + 2 × 15.999 = 147.008 g/mol

With the rounded atomic masses used in many school books (Ca = 40, Cl = 35.5, H = 1, O = 16) the answer is 147 g/mol. The difference from 147.01 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 CaCl2. That water has a mass of 2 × 18.015 = 36.03 g/mol, which is 24.5% of the crystal. Without it, the anhydrous part CaCl2 has a molar mass of 110.98 g/mol. Heating drives the water off, so a sample loses up to 24.5% of its mass. How this is used to find the number of waters is shown on the hydrates page.

Percentage composition

By mass, CaCl2·2H2O is 27.26% calcium, 48.23% chlorine, 2.74% hydrogen and 21.77% oxygen. The largest share comes from chlorine. In a 100 g sample there are 27.3 g of calcium, 48.2 g of chlorine, 2.7 g of hydrogen and 21.8 g of oxygen.

Notice that hydrogen has more atoms in the formula (4) than chlorine (2), 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 20 g of CaCl2·2H2O? Divide the mass by the molar mass: 20 ÷ 147.01 = 0.136 mol.

Moles to grams. What is the mass of 0.5 mol of CaCl2·2H2O? Multiply: 0.5 × 147.01 = 73.5 g.

Counting particles. 20 g contains 0.136 mol × 6.022 × 1023 = 8.193 × 1022 formula units.

Making a solution. A 0.1 mol/L solution contains 0.1 × 147.01 = 14.7 g of CaCl2·2H2O in each litre. For 250 mL, weigh 3.675 g and make it up to the mark with water.

Quick conversion tables

AmountMass
0.1 mol14.7 g
0.5 mol73.5 g
1 mol147 g
2 mol294 g
5 mol735 g
MassMoles
1 g0.006802 mol
10 g0.06802 mol
100 g0.6802 mol
1 kg6.802 mol

For other amounts use the grams and moles converter.

Questions people ask

What is the molar mass of CaCl2.2H2O?

The molar mass of calcium chloride dihydrate (CaCl2.2H2O) is 147.01 g/mol, or 147.008 g/mol before rounding, using IUPAC abridged atomic weights.

How many moles are in 100 g of CaCl2.2H2O?

100 ÷ 147.01 = 0.6802 mol.

What is the mass of one formula unit of CaCl2.2H2O?

Divide the molar mass by the Avogadro constant: 147.01 ÷ 6.022 × 1023 = 2.441 × 10-22 g.

What is the percentage of chlorine in CaCl2.2H2O?

Chlorine makes up 48.23% of the mass of CaCl2.2H2O: 2 × 35.45 ÷ 147.008 × 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.

More hydrates

All hydrates · All compounds