Molar Mass of O₂
Oxygen gas (dioxygen). Oxygen exists as diatomic O₂ molecules, so the molar mass of the gas is twice the atomic mass of oxygen.
Molar mass of O2
31.998 g/mol
2 × 15.999 = 31.998
Calculation, element by element
| Element | Atoms | Atomic mass (g/mol) | Subtotal | Mass % |
|---|---|---|---|---|
| Oxygen (O) | 2 | 15.999 | 31.998 | 100.00% |
| Total | 31.998 | 100% |
= 0.31252 mol = 1.882 × 1023 molecules
O₂ molar mass FAQ
What is the molar mass of oxygen gas (O₂)?
31.998 g/mol. It is the sum of the atomic masses of every atom in the formula: 2 × 15.999 = 31.998 g/mol.
How many grams are in one mole of O₂?
31.998 g. Molar mass is the mass of one mole (6.022 × 10²³ formula units), so 1 mol of O₂ weighs 31.998 g and 0.5 mol weighs 15.999 g.
How many moles are in 10 g of O₂?
10 g ÷ 31.998 g/mol = 0.3125 mol.
What is the percent composition of O₂?
Oxygen 100.00%.
Is molecular weight the same as molar mass for O₂?
Numerically yes: the molecular (or formula) weight is 31.998 u per formula unit, and the molar mass is 31.998 g/mol.
Molar masses of other common compounds
H2O WaterNaCl Sodium chlorideNaOH Sodium hydroxideC6H12O6 GlucoseCO2 Carbon dioxideHCl Hydrochloric acidH2SO4 Sulfuric acidCaCO3 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