Factors that affect Faradays Law of electrolysis

A. Hi Michael. We have a brief and easy to understand presentation on Faraday's Law on line here.

I think Faraday's main point was that you will not find any of those other factors you are looking for because they don't exist :-)

Rather, the point is that one 'Faraday' of electricity (96,485 coulombs or 96,485 ampere-seconds) reduces one gram molecular weight at the cathode, and oxidizes one molecular weight at the anode -- regardless, and period.

But that 'one molecular weight' might not be all one thing. For example if you are doing brass plating (an alloy of zinc and copper), each 96,485 ampere-seconds of electricity might dissolve 0.5 of a molecular weight of copper and dissolve 0.4 of a molecular weight of zinc and liberate 0.1 of a molecular weight of oxygen from the water.
And at the cathode it might plate out 0.6 of a molecular weight of copper and 0.2 of a molecular weight of zinc and liberate 0.2 of a molecular weight of hydrogen from the water. If you really think it through, Faraday's Law essentially says that if you count the number of electrons you moved from anode to cathode, it's going to balance the number of electrons you stripped from atoms at the anode (turning them into positively charged ions) and the number of electrons you added to positively charged ions at the cathode turning them back into atoms ... it's actually quite simple.

When something we set out to do doesn't work 100% the way we would have preferred, we say that it wasn't 100% efficient. In this example, where we were trying to do brass plating onto the cathode, that Faraday of electricity deposited 0.8 molecular weights of brass (0.6 of copper and 0.2 of zinc), and it "wasted" 0.2 of that Faraday in liberating hydrogen. So we say the cathode efficiency was 80%. The cathode efficiency of most plating operations runs somewhere between 70% and 99%; notoriously, chrome plating is only about 12% efficient.

The factors you mention like flow rate and temperature may affect the efficiency though, and perhaps the easiest way to look at is that if there is a great abundance of the metal you wish to deposit available right at the atomic interface of the cathode, the efficiency can be expected to be high whereas if there isn't, the efficiency has to be low. After all, if there's no metal there, you can't plate it out, the electrons get 'wasted' liberating hydrogen. :-)