Molar MassMolar mass of mercury(II) chloride (HgCl2)
The molar mass of mercury(II) chloride, HgCl2, is 271.49 g/mol. One mole of it, which is 6.022 × 1023 formula units, has a mass of 271.49 grams.
271.49 g/mol
200.59 + 2 × 35.45 = 271.490 · 3 atoms in the formula · also called corrosive sublimate
About mercury(II) chloride
Mercury(II) chloride is a very poisonous white solid. Mercury is one of the heaviest common elements, so it gives nearly three quarters of the mass.
Other names: corrosive sublimate.
The working
The formula HgCl2 has 1 mercury 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 |
|---|---|---|---|---|
| Mercury (Hg) | 1 | 200.59 | 200.590 | 73.88% |
| Chlorine (Cl) | 2 | 35.45 | 70.900 | 26.12% |
200.59 + 2 × 35.45 = 271.490 g/mol
With the rounded atomic masses used in many school books (Hg = 201, Cl = 35.5) the answer is 272 g/mol. The difference from 271.49 is too small to matter in most school sums.
Percentage composition
By mass, HgCl2 is 73.88% mercury and 26.12% chlorine. The largest share comes from mercury. In a 100 g sample there are 73.9 g of mercury and 26.1 g of chlorine.
Notice that chlorine has more atoms in the formula (2) than mercury (1), 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 HgCl2? Divide the mass by the molar mass: 20 ÷ 271.49 = 0.07367 mol.
Moles to grams. What is the mass of 0.5 mol of HgCl2? Multiply: 0.5 × 271.49 = 135.7 g.
Counting particles. 20 g contains 0.07367 mol × 6.022 × 1023 = 4.436 × 1022 formula units.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 27.15 g |
| 0.5 mol | 135.7 g |
| 1 mol | 271.5 g |
| 2 mol | 543 g |
| 5 mol | 1357 g |
| Mass | Moles |
|---|---|
| 1 g | 0.003683 mol |
| 10 g | 0.03683 mol |
| 100 g | 0.3683 mol |
| 1 kg | 3.683 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of HgCl2?
The molar mass of mercury(II) chloride (HgCl2) is 271.49 g/mol, or 271.490 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of HgCl2?
100 ÷ 271.49 = 0.3683 mol.
What is the mass of one formula unit of HgCl2?
Divide the molar mass by the Avogadro constant: 271.49 ÷ 6.022 × 1023 = 4.508 × 10-22 g.
What is the percentage of mercury in HgCl2?
Mercury makes up 73.88% of the mass of HgCl2: 1 × 200.59 ÷ 271.490 × 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.