The molar mass of ethanol (C2H6O) is 46.069 g/mol.
Case matters: CO is carbon monoxide, Co is
cobalt. Brackets and hydrates are fine — try
or
.
| Element | Atoms | Atomic mass | Mass contributed | Percent |
|---|---|---|---|---|
| Carbon (C) | 2 | 12.011 | 24.022 | 52.14% |
| Hydrogen (H) | 6 | 1.0080 | 6.048 | 13.13% |
| Oxygen (O) | 1 | 15.999 | 15.999 | 34.73% |
| Total | 9 | 46.069 | 100.00% |
24.022 + 6.048 + 15.999 = 46.069 g/mol
Grams and moles
25 g of ethanol is 0.5427 mol, because 25 ÷ 46.069 = 0.5427.
These elements have no single atomic weight. Their isotopic mix varies slightly depending on where on Earth the sample came from, so the figure used here is the conventional value IUPAC publishes for when one number is needed: carbon is 12.011, and really lies between 12.0096 and 12.0116; hydrogen is 1.0080, and really lies between 1.00784 and 1.00811; oxygen is 15.999, and really lies between 15.99903 and 15.99977.
Ethanol comes to 46.069 g/mol. Its formula is usually written C2H5OH rather than C2H6O, because the condensed version hides the fact that one of those six hydrogens is bonded to oxygen and behaves nothing like the other five.
Either spelling gives the same molar mass, since molar mass only counts atoms. But C2H6O is also dimethyl ether, a gas boiling at -24 degrees Celsius rather than a liquid boiling at 78. Same atoms, same 46.069 g/mol, a completely different substance. These two are the textbook demonstration that a molecular formula does not pin down a molecule.
The number earns its keep in conversions. Alcohol by volume becomes moles through density: a 750 mL bottle at 12% ABV holds 90 mL of ethanol, which at 0.789 g/mL is 71 grams, or about 1.54 moles. Pharmacology and breath-alcohol arithmetic both pass through that step.