Molar MassMolar mass of magnesium chloride (MgCl2)
The molar mass of magnesium chloride, MgCl2, is 95.21 g/mol. One mole of it, which is 6.022 × 1023 formula units, has a mass of 95.21 grams.
About magnesium chloride
Magnesium chloride is found in sea water and is the source from which magnesium metal is made by electrolysis. It is very soluble and takes up moisture from the air.
The working
The formula MgCl2 has 1 magnesium atom and 2 chlorine atoms, 3 atoms in all. Multiply each count by the atomic weight of the element and add:
| Element | Atoms | Atomic weight | Total | Share by mass |
|---|---|---|---|---|
| Magnesium (Mg) | 1 | 24.305 | 24.305 | 25.53% |
| Chlorine (Cl) | 2 | 35.45 | 70.900 | 74.47% |
24.305 + 2 × 35.45 = 95.205 g/mol
With the rounded atomic masses used in many school books (Mg = 24, Cl = 35.5) the answer is 95 g/mol. The difference from 95.21 is too small to matter in most school sums.
Percentage composition
By mass, MgCl2 is 25.53% magnesium and 74.47% chlorine. The largest share comes from chlorine. In a 100 g sample there are 25.5 g of magnesium and 74.5 g of chlorine.
Worked examples
Grams to moles. How many moles are in 10 g of MgCl2? Divide the mass by the molar mass: 10 ÷ 95.21 = 0.105 mol.
Moles to grams. What is the mass of 1.5 mol of MgCl2? Multiply: 1.5 × 95.21 = 142.8 g.
Counting particles. 10 g contains 0.105 mol × 6.022 × 1023 = 6.325 × 1022 formula units.
Making a solution. A 0.1 mol/L solution contains 0.1 × 95.21 = 9.521 g of MgCl2 in each litre. For 250 mL, weigh 2.38 g and make it up to the mark with water.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 9.521 g |
| 0.5 mol | 47.6 g |
| 1 mol | 95.21 g |
| 2 mol | 190.4 g |
| 5 mol | 476 g |
| Mass | Moles |
|---|---|
| 1 g | 0.0105 mol |
| 10 g | 0.105 mol |
| 100 g | 1.05 mol |
| 1 kg | 10.5 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of MgCl2?
The molar mass of magnesium chloride (MgCl2) is 95.21 g/mol, or 95.205 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of MgCl2?
100 ÷ 95.21 = 1.05 mol.
What is the mass of one formula unit of MgCl2?
Divide the molar mass by the Avogadro constant: 95.21 ÷ 6.022 × 1023 = 1.581 × 10-22 g.
What is the percentage of chlorine in MgCl2?
Chlorine makes up 74.47% of the mass of MgCl2: 2 × 35.45 ÷ 95.205 × 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.