Sciencemadness Discussion Board - Electrolysis of water

Electrolysis of water

CoolFool - 4-11-2016 at 07:27

I wanted to show my sister how electrolysis of water works and so i filled a beaker with water and adder salt . I passed a current of 3 v . Some gas was produced but to my surprise there was also formation of a brown precipitate. I checked the salt and found out that it also contained Potassium Iodide :mad:

. I carried it out again but the result was the same. Can someone tell me the cause for this?

violet sin - 4-11-2016 at 07:31

What are your electrodes made from? Could be corrosion

elementcollector1 - 4-11-2016 at 07:37

If your electrodes are steel or iron, that's almost definitely iron(III) hydroxide.

CoolFool - 4-11-2016 at 07:38

No I was using copper wires

crystal grower - 4-11-2016 at 08:09

Then probably copper(I) oxide. Potassium iodide is harmless in this experiment and on top of that, its content in table salt is negligable.
Try stainless steel instead, or maybe carbon rods.

[Edited on 4-11-2016 by crystal grower]

woelen - 4-11-2016 at 08:12

At the anode you get impure copper(I) oxide. This stuff is yellow/brown.
At the cathode you get hydrogen gas.

If you use carbon rods (e.g. from spent zinc batteries), then you get chlorine at the anode, and you can easily smell it. That would be a more understandable demo for your sister.

Sulaiman - 4-11-2016 at 11:21

also, use sodium bicarbonate for the electrolyte as oxygen is slightly more electronegative than chlorine,
so elevtrolysis of sodium chloride solution produces H₂ and Cl₂ and NaOH in solution.
Most of the chlorine will combine with the NaOH but some escapes.
It just makes the explanation of the results easier using bicarbonate.

Matthew - 5-11-2016 at 12:57

You might try getting the graphite out of the pencil. Don't heat up the rods too much though or they will break

Liamatpm - 20-12-2016 at 10:14

You could also get a 6v battery and you'd get 4 carbon electrodes. Also I'd recommend using a high wattage. Remember P=I*E,
P-power in watts
I- ohms
E-Volts

MrHomeScientist - 20-12-2016 at 10:51

To simplify the explanation, a baking soda solution using distilled water and using graphite electrodes would be best. That way you get oxygen and hydrogen, and no complications from reactions with the electrolyte or electrodes.

WGTR - 20-12-2016 at 12:37

Interestingly enough, I just found out that mild, low carbon steel is an excellent low-cost anode for water electrolysis. This is provided that the Na₂CO₃ electrolyte is very pure, i.e., no halogen contamination. Just a few ppm of added NaCl is enough to induce corrosion of the steel anode. With high enough electrolyte purity, however, I've used 1018 steel anodes in a cell for days with little more than a slight color change from a transparent oxide layer. No coloring of the solution was noted, and no loose corrosion products were present.

[Edited on 12-20-2016 by WGTR]

Jstuyfzand - 20-12-2016 at 13:28

Quote: Originally posted by WGTR

Interestingly enough, I just found out that mild, low carbon steel is an excellent low-cost anode for water electrolysis. This is provided that the Na₂CO₃ electrolyte is very pure, i.e., no halogen contamination. Just a few ppm of NaCl is enough to induce corrosion of the steel anode. With high enough electrolyte purity, however, I've used 1018 steel anodes in a cell for days with little more than a slight color change from a transparent oxide layer. No coloring of the solution was noted, and no loose corrosion products were present.

Wouldn't NaOH make for an even better electrolyte? No possible Co2 evolution, ofcourse provided it is pure.

WGTR - 20-12-2016 at 13:59

KOH also seemed to work, although that transparent oxide layer formed more quickly. It does seem to be less pure that the Na₂CO₃, however. Here's what I used:

CoolFool - 29-1-2017 at 03:39

I tried doing the same experiment with all the same stuff but this time i got a green precipitate . Is it copper hydroxide? also the current was 4.5V

Liamatpm - 22-3-2017 at 09:59

It was probably Iron hydroxide. (Like what other people have said) I figured to say what I thought because with more information the better.

[Edited on 22-3-2017 by Liamatpm]

Liamatpm - 22-3-2017 at 10:04

Quote: Originally posted by CoolFool

I tried doing the same experiment with all the same stuff but this time i got a green precipitate . Is it copper hydroxide? also the current was 4.5V

It was the copper like you said.