Molar MassMolar mass of carbonic acid (H2CO3)
The molar mass of carbonic acid, H2CO3, is 62.02 g/mol. One mole of it, which is 6.022 × 1023 molecules, has a mass of 62.02 grams.
About carbonic acid
Carbonic acid forms when carbon dioxide dissolves in water. It is weak and unstable, breaking back into water and carbon dioxide easily, which is why fizzy drinks go flat. Its salts are the carbonates and hydrogencarbonates.
The working
The formula H2CO3 has 2 hydrogen atoms, 1 carbon atom and 3 oxygen atoms, 6 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 | 3.25% |
| Carbon (C) | 1 | 12.011 | 12.011 | 19.37% |
| Oxygen (O) | 3 | 15.999 | 47.997 | 77.38% |
2 × 1.0080 + 12.011 + 3 × 15.999 = 62.024 g/mol
With the rounded atomic masses used in many school books (H = 1, C = 12, O = 16) the answer is 62 g/mol. The difference from 62.02 is too small to matter in most school sums.
Percentage composition
By mass, H2CO3 is 3.25% hydrogen, 19.37% carbon and 77.38% oxygen. The largest share comes from oxygen. In a 100 g sample there are 3.3 g of hydrogen, 19.4 g of carbon and 77.4 g of oxygen.
Worked examples
Grams to moles. How many moles are in 250 g of H2CO3? Divide the mass by the molar mass: 250 ÷ 62.02 = 4.031 mol.
Moles to grams. What is the mass of 0.2 mol of H2CO3? Multiply: 0.2 × 62.02 = 12.4 g.
Counting particles. 250 g contains 4.031 mol × 6.022 × 1023 = 2.427 × 1024 molecules, and 1.456 × 1025 atoms in all.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 6.202 g |
| 0.5 mol | 31.01 g |
| 1 mol | 62.02 g |
| 2 mol | 124 g |
| 5 mol | 310.1 g |
| Mass | Moles |
|---|---|
| 1 g | 0.01612 mol |
| 10 g | 0.1612 mol |
| 100 g | 1.612 mol |
| 1 kg | 16.12 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of H2CO3?
The molar mass of carbonic acid (H2CO3) is 62.02 g/mol, or 62.024 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of H2CO3?
100 ÷ 62.02 = 1.612 mol.
What is the mass of one molecule of H2CO3?
Divide the molar mass by the Avogadro constant: 62.02 ÷ 6.022 × 1023 = 1.030 × 10-22 g.
What is the percentage of oxygen in H2CO3?
Oxygen makes up 77.38% of the mass of H2CO3: 3 × 15.999 ÷ 62.024 × 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.