Molar MassMolar mass of aluminium chloride (AlCl3)
The molar mass of aluminium chloride, AlCl3, is 133.33 g/mol. One mole of it, which is 6.022 × 1023 formula units, has a mass of 133.33 grams.
About aluminium chloride
Anhydrous aluminium chloride is a white solid that fumes in moist air. It is an important catalyst in organic chemistry, in the Friedel-Crafts reactions.
The working
The formula AlCl3 has 1 aluminium atom and 3 chlorine atoms, 4 atoms in all. Multiply each count by the atomic weight of the element and add:
| Element | Atoms | Atomic weight | Total | Share by mass |
|---|---|---|---|---|
| Aluminium (Al) | 1 | 26.982 | 26.982 | 20.24% |
| Chlorine (Cl) | 3 | 35.45 | 106.350 | 79.76% |
26.982 + 3 × 35.45 = 133.332 g/mol
With the rounded atomic masses used in many school books (Al = 27, Cl = 35.5) the answer is 133.5 g/mol. The difference from 133.33 is too small to matter in most school sums.
Percentage composition
By mass, AlCl3 is 20.24% aluminium and 79.76% chlorine. The largest share comes from chlorine. In a 100 g sample there are 20.2 g of aluminium and 79.8 g of chlorine.
Worked examples
Grams to moles. How many moles are in 40 g of AlCl3? Divide the mass by the molar mass: 40 ÷ 133.33 = 0.3 mol.
Moles to grams. What is the mass of 3 mol of AlCl3? Multiply: 3 × 133.33 = 400 g.
Counting particles. 40 g contains 0.3 mol × 6.022 × 1023 = 1.807 × 1023 formula units.
Making a solution. A 0.1 mol/L solution contains 0.1 × 133.33 = 13.33 g of AlCl3 in each litre. For 250 mL, weigh 3.333 g and make it up to the mark with water.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 13.33 g |
| 0.5 mol | 66.67 g |
| 1 mol | 133.3 g |
| 2 mol | 266.7 g |
| 5 mol | 666.7 g |
| Mass | Moles |
|---|---|
| 1 g | 0.0075 mol |
| 10 g | 0.075 mol |
| 100 g | 0.75 mol |
| 1 kg | 7.5 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of AlCl3?
The molar mass of aluminium chloride (AlCl3) is 133.33 g/mol, or 133.332 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of AlCl3?
100 ÷ 133.33 = 0.75 mol.
What is the mass of one formula unit of AlCl3?
Divide the molar mass by the Avogadro constant: 133.33 ÷ 6.022 × 1023 = 2.214 × 10-22 g.
What is the percentage of chlorine in AlCl3?
Chlorine makes up 79.76% of the mass of AlCl3: 3 × 35.45 ÷ 133.332 × 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.