Molar MassMolar mass of iron(III) chloride (FeCl3)
The molar mass of iron(III) chloride, FeCl3, is 162.19 g/mol. One mole of it, which is 6.022 × 1023 formula units, has a mass of 162.19 grams.
162.19 g/mol
55.845 + 3 × 35.45 = 162.195 · 4 atoms in the formula · also called ferric chloride
About iron(III) chloride
Iron(III) chloride is a dark solid that gives a yellow-brown solution. It is used to etch copper on circuit boards and to treat water. Its solution gives a violet colour with phenols.
Other names: ferric chloride.
The working
The formula FeCl3 has 1 iron 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 |
|---|---|---|---|---|
| Iron (Fe) | 1 | 55.845 | 55.845 | 34.43% |
| Chlorine (Cl) | 3 | 35.45 | 106.350 | 65.57% |
55.845 + 3 × 35.45 = 162.195 g/mol
With the rounded atomic masses used in many school books (Fe = 56, Cl = 35.5) the answer is 162.5 g/mol. The difference from 162.19 is too small to matter in most school sums.
Percentage composition
By mass, FeCl3 is 34.43% iron and 65.57% chlorine. The largest share comes from chlorine. In a 100 g sample there are 34.4 g of iron and 65.6 g of chlorine.
Worked examples
Grams to moles. How many moles are in 50 g of FeCl3? Divide the mass by the molar mass: 50 ÷ 162.19 = 0.3083 mol.
Moles to grams. What is the mass of 0.4 mol of FeCl3? Multiply: 0.4 × 162.19 = 64.88 g.
Counting particles. 50 g contains 0.3083 mol × 6.022 × 1023 = 1.856 × 1023 formula units.
Making a solution. A 0.1 mol/L solution contains 0.1 × 162.19 = 16.22 g of FeCl3 in each litre. For 250 mL, weigh 4.055 g and make it up to the mark with water.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 16.22 g |
| 0.5 mol | 81.1 g |
| 1 mol | 162.2 g |
| 2 mol | 324.4 g |
| 5 mol | 811 g |
| Mass | Moles |
|---|---|
| 1 g | 0.006165 mol |
| 10 g | 0.06165 mol |
| 100 g | 0.6165 mol |
| 1 kg | 6.165 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of FeCl3?
The molar mass of iron(III) chloride (FeCl3) is 162.19 g/mol, or 162.195 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of FeCl3?
100 ÷ 162.19 = 0.6165 mol.
What is the mass of one formula unit of FeCl3?
Divide the molar mass by the Avogadro constant: 162.19 ÷ 6.022 × 1023 = 2.693 × 10-22 g.
What is the percentage of chlorine in FeCl3?
Chlorine makes up 65.57% of the mass of FeCl3: 3 × 35.45 ÷ 162.195 × 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.