I am a bit confused on how faraday determined his constant. So I’ve been taught that he realized that if you sent a certain amount of charge (96485 C), then one mole (or some fraction of that based on the ionization) of a substance would be deposited. But how did he know what one mole of a substance was because Avogadro’s number was found by dividing the faraday by the charge of an electron. So it seems like a little bit of circular definition? Like if he used silver, how did he know what 1 mole of silver was because he couldn’t know what the molar mass of silver is if Avogadro’s number hadn’t been found then?


closed as off-topic by Gert, John Rennie, sammy gerbil, M. Enns, Feynmans Out for Grumpy Cat Mar 12 at 0:09

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    $\begingroup$ I'm voting to close this question as off-topic because it belongs in history of physics/chemistry. $\endgroup$ – Gert Mar 11 at 2:06
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    $\begingroup$ @Gert I don't agree the question is about history. Its first words (how faraday determined his constant) could be read that way but when the OP writes how did he know what 1 mole of silver was because he couldn't know what the molar mass of silver is if Avogadro's number hadn't been found then? his question becomes one about logic of the matter. He's in need of understanding that there are several possible definitions of molar mass, among which those involving only ratios of masses participating in a reaction. $\endgroup$ – Elio Fabri Mar 12 at 16:35
  • $\begingroup$ @Gert Avogadro's constant isn't necessarily involved and actually it didn't, for a long time. But this isn't a historical matter. $\endgroup$ – Elio Fabri Mar 12 at 16:36
  • $\begingroup$ @ElioFabri This reads history-based to me. This could certainly be edited into a form that asks explicitly (and only) about the logic, but the current text reads history-based. $\endgroup$ – Emilio Pisanty Mar 13 at 12:44