Sciencemadness Discussion Board

How to tell when electrolysis has reached completion?

cobalt_catalyst - 20-4-2012 at 11:54

I have been doing some experiments involving electrolysis lately. Most recently the electrolysis of iron to form Iron(III) Hydroxide. I have had no lapses in terms of the procedure but I don't know when to stop. How do you tell when An electrolysis is complete? Does the electrolyte get used up? Also what specific topic in electrochemistry would this be so I can read about it

Hexavalent - 20-4-2012 at 12:25

Electrolysis is complete when the electrolyte is used up, to simplify it. There is often a measurable difference between what you started with and a calculated expected value for the end of the electrolysis, e.g. pH. A complete colour change is also another one to look out for, as is formation of precipitates.

I'm certain other, more seasoned, chemists will be able to give you more.

What procedure did you take for the electrolysis of iron, out of curiosity?

cobalt_catalyst - 20-4-2012 at 13:12

I used a carbon cathode and an iron anode in a solution of NaHCO3 as the electrolyte. It is powered by a 12V battery that can supply at least 10 amps. As for the mechanism for the reaction I'm not exactly sure but the chemical equation is: 4 Fe + 3 O2 + 2H2O ------> 4 FeO(OH)

weiming1998 - 20-4-2012 at 16:12

Quote: Originally posted by cobalt_catalyst  
I used a carbon cathode and an iron anode in a solution of NaHCO3 as the electrolyte. It is powered by a 12V battery that can supply at least 10 amps. As for the mechanism for the reaction I'm not exactly sure but the chemical equation is: 4 Fe + 3 O2 + 2H2O ------> 4 FeO(OH)


Because NaHCO3 is an inert electrolyte, this reaction will not consume it. There are only two ways that your electrolysis can reach completion.

Either all of your iron anode is eroded away or all the water is converted to H2 and O2. But if you are just harvesting iron hydroxide, you can stop the electrolysis once the amount of iron hydroxide that you require precipitates at the bottom (it is insoluble).