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Author: Subject: Usefulness of Lead electrodes to perform electrolysis
Dagda_Mor
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[*] posted on 18-6-2016 at 05:19
Usefulness of Lead electrodes to perform electrolysis


Recently I have conducted some small experiments in order to test the usefulness of using lead as electrode. I have used 5A at 12V DC in all three cases.

Here are my experiments :

1) Using my 2 lead electrodes I tried to electrolyse outdoors 20% solution of NaCl in distilled water. As expected a strong smell of chlorine was noticed. But also a strange orange-colored solid deposited at the bottom of the vessel. It is obviously a lead salt, but neither PbCl2 (which also must be formed at the anode), nor Pb(OH)2, as both are white in color. One ot the lead oxides is supposed to be formed by the O- ions underwater at the cathode but it is unclear why Pb(OH)2 wasn't formed, but lead oxide ?

2) The entire vessel and the lead electrodes were washed thoroughly with water and the same experiment was conducted using tap water with no added salts. No gas evolution was noticed at the electrodes, but once again a formation of deposits was noticed at the cathode. This time the deposit was a white solid, which must be Pb(OH)2.

3) In order to try something more fun, a solution of 5% KMnO4 was electolysed using the same lead electrodes. No change of the deep purple color of the solution was noticed, contrary to the expected reduction of the oxidation state of manganese.

You will probably laugh at my noob-like experiments in the field ot inorganic chemistry, but I want to ask 3 simple question about the reaction mechanics when conducting electrolysis using lead electrodes :

1- Why when I electrolyse brine, lead oxides are formed, contrary to the expected lead hydroxide?

2- In the case of electrolysing KMnO4 why no change of color was noticed? Probably because by using lead electrodes oxidation is prefered to reduction and the oxidation state of manganese is the highest in KMnO4.

3- I have read a topic about the formation of manganese-ammonium alum using lead electrodes in conc. H2SO4. As I see it is highly likely that some sort of lead salt will be formed at the cathode - lead oxide or lead sulphate.
Therefore some loss of lead from the electrodes is inevitable. Won't the cathode be totally corroded over time, and won't the lead salts contaminate the final alum product ?

Link to the topic of the manganese-ammonium alum :
http://www.sciencemadness.org/talk/viewthread.php?tid=6882

Thanks in advance for your clarification of the abovementioned observations and questions !
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hissingnoise
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[*] posted on 18-6-2016 at 06:21


Quote:
Why when I electrolyse brine, lead oxides are formed, contrary to the expected lead hydroxide?

It's lead chloride, actually ─ this salt may be white, orange or sometimes green!

And KMnO4 itself is obtained by electrolysis of K2MnO4.

A less reactive anode than lead is required, obviously, and graphite and carbon make reasonable, cheap alternatives!

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