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Author: Subject: Electrolysis of FeSO4

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[*] posted on 19-11-2005 at 06:06
Electrolysis of FeSO4

For a school experiment me and my friend dissolved iron sulphate in distilled water and electrolyzed it. We used carbon rods.
However after the experiment, we didn't discover any Fe on the negative rod (which is where it should go?). maybe because the carbon rod was black and the iron is black too so hard to see. My question, is there supposed to be iron produced on the negative rod?

We used the same carbon rods to electrolyze salt dissolved in water. We could clearly smell the chlorine gas but we got no sodium coating on the rod. Is there supposed to be a coating of sodium? and if not then why?

Help would be appreciated.
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[*] posted on 19-11-2005 at 10:04

First the question on sodium. Have you ever seen a piece of sodium thrown in water? What happens with that? Now you should understand why sodium cannot be formed by electrolysis of an aqueous solution of table salt.

The iron part is somewhat more tricky. Iron is a border-line metal with respect to electrolysis. Iron in fact is quite reactive (we see this around us, rusting of iron objects). The solution you have is slightly acidic due to hydrolysis of the iron salt. The electropositivity of iron is such that it dissolves in acid and not in water. Under the electrolysis conditions it is more favorable to form hydrogen gas. I can imagine that increasing the voltage or using another iron salt, which allows a slightly higher pH before the iron is precipitated (e.g. FeCl2), that you can obtain some iron metal on the cathode. But indeed, making iron by means of electrolysis is not easy, is I also have noticed personally.

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[*] posted on 19-11-2005 at 16:49

Use an iron anode.


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[*] posted on 20-11-2005 at 09:37

"Use an iron anode. "
Or don't - that way when the colour from the Fe++ grows faint you will know that you have removed the iron from solution even if you cant see it on the carbon rods.

Of course, this is complicated by the fact that Fe++ will get oxidiesd to Fe+++ at the +ve electrode but you might see the effect with an unstirred solution.

Scraping the stuff of the cathode, suspending it in water and adding a magnet might show up any iron produced .
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