Molar MassMolar mass of hydrogen sulphide (H2S)
The molar mass of hydrogen sulphide, H2S, is 34.08 g/mol. One mole of it, which is 6.022 × 1023 molecules, has a mass of 34.08 grams.
34.08 g/mol
2 × 1.0080 + 32.06 = 34.076 · 3 atoms in the formula · also called hydrogen sulfide
About hydrogen sulphide
Hydrogen sulphide is a poisonous gas with the smell of rotten eggs. In water it behaves as a weak acid. It was long used in qualitative analysis to precipitate metal sulphides, and it is slightly heavier than air.
Other names: hydrogen sulfide.
The working
The formula H2S has 2 hydrogen atoms and 1 sulphur atom, 3 atoms in all. Multiply each count by the atomic weight of the element and add:
| Element | Atoms | Atomic weight | Total | Share by mass |
|---|---|---|---|---|
| Hydrogen (H) | 2 | 1.0080 | 2.016 | 5.92% |
| Sulphur (S) | 1 | 32.06 | 32.060 | 94.08% |
2 × 1.0080 + 32.06 = 34.076 g/mol
With the rounded atomic masses used in many school books (H = 1, S = 32) the answer is 34 g/mol. The difference from 34.08 is too small to matter in most school sums.
Percentage composition
By mass, H2S is 5.92% hydrogen and 94.08% sulphur. The largest share comes from sulphur. In a 100 g sample there are 5.9 g of hydrogen and 94.1 g of sulphur.
Notice that hydrogen has more atoms in the formula (2) than sulphur (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 50 g of H2S? Divide the mass by the molar mass: 50 ÷ 34.08 = 1.467 mol.
Moles to grams. What is the mass of 0.4 mol of H2S? Multiply: 0.4 × 34.08 = 13.63 g.
Counting particles. 50 g contains 1.467 mol × 6.022 × 1023 = 8.836 × 1023 molecules, and 2.651 × 1024 atoms in all.
As a gas. At 0 °C and 1 atmosphere one mole of an ideal gas occupies 22.4 litres, so the density of H2S is about 34.08 ÷ 22.4 = 1.52 g per litre. Air averages about 29 g/mol, so this gas is heavier than air.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 3.408 g |
| 0.5 mol | 17.04 g |
| 1 mol | 34.08 g |
| 2 mol | 68.15 g |
| 5 mol | 170.4 g |
| Mass | Moles |
|---|---|
| 1 g | 0.02935 mol |
| 10 g | 0.2935 mol |
| 100 g | 2.935 mol |
| 1 kg | 29.35 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of H2S?
The molar mass of hydrogen sulphide (H2S) is 34.08 g/mol, or 34.076 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of H2S?
100 ÷ 34.08 = 2.935 mol.
What is the mass of one molecule of H2S?
Divide the molar mass by the Avogadro constant: 34.08 ÷ 6.022 × 1023 = 5.658 × 10-23 g.
What is the percentage of sulphur in H2S?
Sulphur makes up 94.08% of the mass of H2S: 1 × 32.06 ÷ 34.076 × 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.