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shmootz t1_itpok6v wrote

Reply to comment by Felinomancy in TIL Amedeo Avogadro's contribution to chemistry, known as Avogadro's law, did not initially receive much attention when he published his paper in 1811. It was only a century later that his work was recognized, when the King of Italy attended a meeting commemorating the paper's 100th anniversary. by dustofoblivion123

>The value of the Avogadro constant was chosen so that the mass of one mole of a chemical compound, in grams, is numerically equal (for all practical purposes) to the average mass of one molecule of the compound in daltons (universal atomic mass units); one dalton being 1/12 of the mass of one carbon-12 atom, which is approximately the mass of one nucleon (proton or neutron). For example, the average mass of one molecule of water is about 18.0153 daltons, and one mole of water (N molecules) is about 18.0153 grams.

For your example, there are many isotopes of carbon, where extra nuetrons are stuck to the molecule, increasing weight.

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Nietzschemouse t1_itqib6t wrote

Definitely a typo because 15.99 is oxygen's value. Almost definitely not a carbon isotope issue

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Bradley5345 t1_itqqvrt wrote

The molar masses reported on the periodic table account for this by being a weighted average of the masses of any isotopes multiplied by their fractional abundance as they occur in nature. Also, it’s neutrons. Hence, when he said average mass, he was accounting for what you’re saying. There’s a reason these molar masses aren’t whole numbers.

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