Molar Mass of Water
H2O — 18.015 g/mol, worked out element by element.
Molar mass of Water, H₂O
18.015 g/mol
Molecular weight 18.015 · 3 atoms per formula unit
Also known as: dihydrogen monoxide, h2o, aqua.
The reference substance for the mole, for density and for specific heat, and the solvent almost every solution problem assumes.
How 18.015 g/mol is worked out
| Element | Atoms | Atomic mass | Mass | % of total |
|---|---|---|---|---|
| Oxygen | 1 | 15.999 | 15.999 | 88.81% |
| Hydrogen | 2 | 1.008 | 2.016 | 11.19% |
| Total | 3 | 18.015 | 100% |
M = 1 × 15.999 + 2 × 1.008 = 18.015 g/mol
Grams to moles for Water
| Mass | Moles | Formula units |
|---|---|---|
| 1 g | 0.0555 mol | 3.343 × 10^22 |
| 10 g | 0.5551 mol | 3.343 × 10^23 |
| 25 g | 1.3877 mol | 8.357 × 10^23 |
| 50 g | 2.7755 mol | 1.671 × 10^24 |
| 100 g | 5.5509 mol | 3.343 × 10^24 |
| 250 g | 13.8773 mol | 8.357 × 10^24 |
| 18.015 g | 1 mol | 6.022 × 10^23 |
For any other amount, use the molar mass calculator, or the molarity calculator to make up a solution of a given concentration.
Related compounds
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Frequently Asked Questions
What is the molar mass of Water?
The molar mass of Water (H2O) is 18.015 g/mol. That is the sum of the standard atomic weights of all 3 atoms in one formula unit: 1 × 15.999 + 2 × 1.008 = 18.015.
What is the molecular weight of Water?
18.015 — the same number as the molar mass, but as a dimensionless ratio rather than in g/mol. The two terms describe the same arithmetic, so a molecular weight of 18.02 and a molar mass of 18.02 g/mol are the same answer.
How many moles are in 100 g of Water?
100 ÷ 18.015 = 5.5509 mol. To convert any mass to moles, divide by the molar mass; to go the other way, multiply.
What is the percent composition of Water?
By mass, Water is 88.81% oxygen, 11.19% hydrogen. Each element's share is its total mass in the formula divided by 18.015.
How many atoms are in one formula unit of Water?
3: 1 oxygen, 2 hydrogen. One mole contains 6.02214076 × 10²³ formula units, so a mole of Water contains 3 × 6.022 × 10²³ atoms in total.