[nzbru]

Hey, as part of an EEI we were given the task of restoring some rusted iron nails by using electrolysis. To do this my group used Na2CO3 as an electrolyte and varied both the voltage and anode. Zinc and stainless steel were used as the anodes and the voltage was adjusted throughout the trials. A diagram of the setup can be seen in the image below:



As per required, I have been asked to explain the chemical processes occurring and I understand most of what is happening. So far this is what I have (I am not sure if this is correct, this EEI is not being drafted for some odd reason):

The molecules which can react with each other are: Na2CO3, H2O, Zn, Stainless Steel (is an alloy but I have looked at reactions involving chromoum and iron), the iron cathode itself and the rust (Fe2O3). The electrolyte can react with the water to form H2CO3 and 2NaOH. The zinc and the electrolyte can form to make ZnCO3+2Na. The iron and the electrolyte can form to make FeCO3+2Na. I cannot find any other possible reactions occurring (of course I know the reactions in relation to the oxidation of the zinc to form ZnO (I am not quite shore about stainless steel as it is an alloy but it does rust).

I do not know how to explain the colour change which occurs in the solution. So far I think that it is the zinc oxide dissolving in the solution but the solution becomes pretty white. I am also not 100% confident on my explanations regarding the reactions occurring. I know the electrolyte is used to make the water more conductive so an electrical current can be created to allow the zinc/stainless steel to oxidize and the iron to reduce. The rust can react with the split hydrogen atoms from the water to produce H20 and Fe. I am just not sure if what I am saying is correct and what else I should be talking about.

Thank you for reading this, I am just wondering if you have any suggestions or corrections to the current things which I have discussed. Cheers, NZBRU.

[Arkcon]

Lets try to simplify the question, just to start with, then add what we know as we go along.  Your plan, to list every possible reaction between every possible component, is a little confusing.

What is the reaction you hope to happen with the current and the rusted iron?  Write that out.  If it did in fact happen, we know what is consumed, and what is produced.  That would be useful.

Try to describe the color change better -- only you were there, and the observations you make are important.  "Pretty white" means what exactly -- was it an attractive shade of white?  Because that's not really a useful scientific term.  Do you mean fairly white?  As in, more than slightly white but less than very white?  Again, not useful terms.  What color did it start?  Clear?  So white in that case means cloudy white?  That's called a precipitate.  That is useful information -- it means something insoluble formed, that will help us identify it when we try to look up possible compounds.

[nzbru]

Sorry if this message is very large but without further or do:

Well, here is the method:

1. The required equipment was gathered and placed on an open bench
2. The equipment was cleaned, if it was deemed necessary.
3. The Alligator clips were connected to the both the positive and negative ends of the power source.
4. The negative end was connected to the black end on the Ammeter.
5. The Ammeter was connected to the nail using an alligator clip.
6. The positive end was connected to the anode.
7. 250ml of two molar washing soda solution was measured and placed in the container.
8. The power box was plugged into a wall socket while ensuring the switch was set to “off”.
9. The pH of the liquid was measured to ensure it was constant throughout the experiments.
10. Everything was double checked and it was made sure that the correct terminals were connected to the correct ends.
11. The predetermined voltage was set on the box. [6/12V]
12. The electricity was turned on and it was allowed to run through the setup.
13. The timer was started when the power switch was turned on and it was left to run for the predetermined time. [15/30/120M]
14. The ammeter was adjusted until a reading was displayed.
15. The power source was disconnected once the desired time was reached.
16. The nail was removed and observations were recorded.
17. Observations about the anode and any possible points of error were also recorded.
18. Notes about the temperature of the solution were taken afterwards.
19. Any needed data was recorded and collated into tables and graphs.
20. The equipment was cleaned and put away.
21. Steps 1-16 were repeated as many times as necessary, the anode and voltage were adjusted if it was deemed necessary

Here is a picture of the beaker half way through one of the trials when we used zinc as our anode (we did about twelve trials in total, varying the time, voltage and anode).



The electrolyte to start was clear and was composed of 2 molar of Na2CO3 per 1000ml of water. Throughout the reaction the water became progressively cloudy (the image is basically the most cloudy each trial went). I am trying to find all of the possible reactions is to explain all of the different things that could have happened when the electrolysis occurred and how that could have effected the results. As no specific information relating to the electrolysis of rusted iron it is hard to find what is actually happening. I suppose after examining it you could say that the zinc oxide does not actually dissolve but it seems to remain in the solution somehow.

Thank you for your quick response. Cheers, NZBRU.

[billnotgatez]

in your picture the nail does not look rusty
just curious

[nzbru]

Whoops, that was strangely a picture of the electrolysis tank when using a stainless steel anode (for some reason the voltage had an impact on the change in colour) here is the correct picture that I was referring to:

[nzbru]

My other group member seems to think that the bi carb from the solution is going onto the zinc. So far I think this (I could be completely wrong):

Because I found the reaction: Zn+Na2CO3 -> ZnCO3+2Na (that could be incorrect) if its the zinc oxide thats HCO3+ZnO which I cannot find any equation for.
Hmm, I found something similar which is Na2CO3+2H2O -> H2CO3+2NaOH but the electrolyte splits up into its ions when in solution
so: CO3+H -> H(CO3)2 or H2CO3. Then H2CO3+Zn -> ZnCO3 + H2 which doesn't seem to make sense as zinc oxide is ZnO
zinc oxide is just formed with zinc and oxygen Zn+O->ZnO
and the oxygen ions are negatively charged so wouldn't they be attracted to the zinc anode and oxidize the zinc

that is my thought process so far