The molar mass of caffeine (C8H10N4O2) is 194.194 g/mol.
Case matters: CO is carbon monoxide, Co is
cobalt. Brackets and hydrates are fine — try
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| Element | Atoms | Atomic mass | Mass contributed | Percent |
|---|---|---|---|---|
| Carbon (C) | 8 | 12.011 | 96.088 | 49.48% |
| Hydrogen (H) | 10 | 1.0080 | 10.080 | 5.19% |
| Nitrogen (N) | 4 | 14.007 | 56.028 | 28.85% |
| Oxygen (O) | 2 | 15.999 | 31.998 | 16.48% |
| Total | 24 | 194.194 | 100.00% |
96.088 + 10.080 + 56.028 + 31.998 = 194.194 g/mol
Grams and moles
25 g of caffeine is 0.1287 mol, because 25 ÷ 194.194 = 0.1287.
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; nitrogen is 14.007, and really lies between 14.00643 and 14.00728; oxygen is 15.999, and really lies between 15.99903 and 15.99977.
Caffeine is 194.194 g/mol. Carbon holds 49.48% of the weight, nitrogen 28.85%, oxygen 16.48% and hydrogen 5.19%.
That nitrogen fraction is the giveaway. Four nitrogens in a molecule this size marks caffeine as an alkaloid, the family of nitrogen-containing plant compounds that includes nicotine, morphine and quinine, and it is why caffeine is mildly basic and forms salts with acids. Caffeine citrate, used in neonatal medicine, is one such salt.
The molar mass converts a dose into something a chemist can reason about. A standard cup of brewed coffee delivers roughly 95 mg, which is 0.49 millimoles, or about 2.9 x 1020 molecules. The commonly cited lethal dose of around 10 grams is some 51 millimoles, which is why a caffeine overdose requires concentrated tablets or powder rather than coffee.
Its structure is a purine, the same ring skeleton found in adenine and guanine in DNA, which is why caffeine can interfere with adenosine receptors in the first place.