In 1834, Michael Faraday stated the exact mathematical
relationship between the amount of electricity consumed and chemicals produced
The mass of a substance generated at an electrode is
proportional to the amount of electricity passed during electrolysis; in
numerical terms, 96,493.1 absolute coulombs of electricity (1 coulomb = 1 amp
second) produce exactly one gram equivalent of a substance by electrolysis.
For those whose recollection of high school chemistry may be a bit fuzzy, the gram equivalent of a substance, according to the Handbook of Chemistry and Physics, is "...the weight of a substance displacing or otherwise reacting with 1.008 g of hydrogen or combining with one-half of a gram atomic weight (8.00 g) of oxygen” (that didn't help much, did it?). For a simpler explanation of gram equivalent, consider that the rate of electrodeposition of a metal at the cathode depends on the number of electrons required to do the job, i. e., to convert the ions in solution to the metallic form. For example, copper in a copper sulfate (CuSO4) solution will be in the form of Cu++ ions, so two electrons (2e-) are required to neutralize the charge of each copper ion, and to deposit one atomic weight of metallic Cu (63.54 g) at the cathode. In other words, Faraday’s 96,493.1 coulombs (i. e., 96,493.1 amp second) will deposit 63.54 / 2 = 31.77 g of metallic Cu at the cathode.
Faraday made other contributions to the understanding of electricity; for more on Faraday click on the picture below:
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