Molar MassMolar mass of lead(II) iodide (PbI2)
The molar mass of lead(II) iodide, PbI2, is 461.00 g/mol. One mole of it, which is 6.022 × 1023 formula units, has a mass of 461.00 grams.
About lead(II) iodide
Lead(II) iodide is the bright yellow precipitate formed when lead nitrate and potassium iodide solutions are mixed, a favourite demonstration of precipitation.
The working
The formula PbI2 has 1 lead atom and 2 iodine 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 |
|---|---|---|---|---|
| Lead (Pb) | 1 | 207.2 | 207.200 | 44.95% |
| Iodine (I) | 2 | 126.90 | 253.800 | 55.05% |
207.2 + 2 × 126.90 = 461.000 g/mol
With the rounded atomic masses used in many school books (Pb = 207, I = 127) the answer is 461 g/mol. The difference from 461.00 is too small to matter in most school sums.
Percentage composition
By mass, PbI2 is 44.95% lead and 55.05% iodine. The largest share comes from iodine. In a 100 g sample there are 44.9 g of lead and 55.1 g of iodine.
Worked examples
Grams to moles. How many moles are in 40 g of PbI2? Divide the mass by the molar mass: 40 ÷ 461.00 = 0.08677 mol.
Moles to grams. What is the mass of 3 mol of PbI2? Multiply: 3 × 461.00 = 1383 g.
Counting particles. 40 g contains 0.08677 mol × 6.022 × 1023 = 5.225 × 1022 formula units.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 46.1 g |
| 0.5 mol | 230.5 g |
| 1 mol | 461 g |
| 2 mol | 922 g |
| 5 mol | 2305 g |
| Mass | Moles |
|---|---|
| 1 g | 0.002169 mol |
| 10 g | 0.02169 mol |
| 100 g | 0.2169 mol |
| 1 kg | 2.169 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of PbI2?
The molar mass of lead(II) iodide (PbI2) is 461.00 g/mol, or 461.000 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of PbI2?
100 ÷ 461.00 = 0.2169 mol.
What is the mass of one formula unit of PbI2?
Divide the molar mass by the Avogadro constant: 461.00 ÷ 6.022 × 1023 = 7.655 × 10-22 g.
What is the percentage of iodine in PbI2?
Iodine makes up 55.05% of the mass of PbI2: 2 × 126.90 ÷ 461.000 × 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.