The molar mass of benzene (C6H6) is 78.114 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) | 6 | 12.011 | 72.066 | 92.26% |
| Hydrogen (H) | 6 | 1.0080 | 6.048 | 7.74% |
| Total | 12 | 78.114 | 100.00% |
72.066 + 6.048 = 78.114 g/mol
Grams and moles
25 g of benzene is 0.3200 mol, because 25 ÷ 78.114 = 0.3200.
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.
Benzene is 78.114 g/mol, and 92.26% of that is carbon. Six hydrogens contribute only 6.048 g/mol between them, giving benzene the highest carbon fraction of any common liquid on a stockroom shelf.
That ratio was the puzzle. A six-carbon chain should carry fourteen hydrogens; benzene carries six, which means an unusually low hydrogen count that early chemists could not reconcile with any straight-chain structure. Kekule’s ring resolved it, and the alternating double bonds that the ring implied turned out to be a delocalised electron system rather than fixed alternating bonds.
The empirical formula is CH, which reduces as far as a formula can. Determining that benzene is C6H6 rather than C2H2 or C4H4 needed a molar mass measurement, and acetylene at 26.038 g/mol is the C2H2 that shares the same empirical formula.
Benzene is a confirmed human carcinogen and has been removed from general laboratory use, with toluene usually taking its place.