Molar Mass of H₂O
Water (H₂O). Two hydrogen atoms and one oxygen atom. One mole of water is about 18 g, roughly a tablespoon.
Molar mass of H2O
18.015 g/mol
2 × 1.008 + 1 × 15.999 = 18.015
Calculation, element by element
| Element | Atoms | Atomic mass (g/mol) | Subtotal | Mass % |
|---|---|---|---|---|
| Hydrogen (H) | 2 | 1.008 | 2.016 | 11.19% |
| Oxygen (O) | 1 | 15.999 | 15.999 | 88.81% |
| Total | 18.015 | 100% |
= 0.55509 mol = 3.3428 × 1023 formula units
H₂O molar mass FAQ
What is the molar mass of water (H₂O)?
18.015 g/mol. It is the sum of the atomic masses of every atom in the formula: 2 × 1.008 + 1 × 15.999 = 18.015 g/mol.
How many grams are in one mole of H₂O?
18.015 g. Molar mass is the mass of one mole (6.022 × 10²³ formula units), so 1 mol of H₂O weighs 18.015 g and 0.5 mol weighs 9.008 g.
How many moles are in 10 g of H₂O?
10 g ÷ 18.015 g/mol = 0.5551 mol.
What is the percent composition of H₂O?
Hydrogen 11.19%, Oxygen 88.81%.
Is molecular weight the same as molar mass for H₂O?
Numerically yes: the molecular (or formula) weight is 18.015 u per formula unit, and the molar mass is 18.015 g/mol.
Molar masses of other common compounds
NaCl Sodium chlorideNaOH Sodium hydroxideC6H12O6 GlucoseCO2 Carbon dioxideHCl Hydrochloric acidH2SO4 Sulfuric acidO2 Oxygen gasCaCO3 Calcium carbonateC2H5OH EthanolNH3 AmmoniaN2 Nitrogen gasCH4 MethaneCuSO4 Copper(II) sulfateKMnO4 Potassium permanganateMgCl2 Magnesium chlorideCuSO4·5H2O Copper(II) sulfate pentahydrateNaHCO3 Sodium bicarbonateNa2CO3 Sodium carbonateKCl Potassium chlorideHNO3 Nitric acidH3PO4 Phosphoric acidCH3COOH Acetic acidC12H22O11 SucroseH2O2 Hydrogen peroxideCa(OH)2 Calcium hydroxideFe2O3 Iron(III) oxideAl2O3 Aluminium oxideAgNO3 Silver nitrateNH4NO3 Ammonium nitrateC8H10N4O2 CaffeineC9H8O4 AspirinC3H8 PropaneC8H18 OctaneH2 Hydrogen gasCl2 Chlorine gasO3 OzoneCO Carbon monoxideSO2 Sulfur dioxideKOH Potassium hydroxideMgO Magnesium oxideCaCl2 Calcium chlorideNaNO3 Sodium nitrateK2Cr2O7 Potassium dichromateBaSO4 Barium sulfate