Please Help! Science Fair Project about Electrolysis

snowfire123 · Post by **snowfire123** » Sun Mar 12, 2006 2:49 pm

I am doing a science project on electrolysis. For the project I am adding different types of salts and other minerals. When I added magnesium sulphate (Epsom salt) it produced a white flaky material. Does anyone have any ideas of what this might be?

-Any help would be greatly appreciated.

mkeaton · Post by **mkeaton** » Sun Mar 12, 2006 3:37 pm

The white flaky material might be a precipitate from a side reaction between water and the sulfate ion or perhaps some other ions in the water (try using deionized water and see if you get the same result). I know that magnesium from magnesium sulfate sometimes causes unwanted white buildup in pipes and drains, especailly of older houses, but I had a feeling this was some kind of reaction with the pipe. The following website might help you understand this mechanism:

http://www.health.state.mn.us/divs/eh/w ... tml#HowCan

(look under how to remove sulfate from water)

I'm sorry my response couldn't be more specific. I tried several google searches and didn't come up with any definitive answers. I'll try my chem textbook and get back to you if I find anything helpful. In the meantime, if you have any more questions feel free to ask!

Michael

snowfire123 · Post by **snowfire123** » Sun Mar 12, 2006 5:15 pm

I forgot to add this in the previous message: Why do you think the reaction is happening in only the oxygen side? Sorry for forgetting to add this in the previous message.

snowfire123 · Post by **snowfire123** » Sun Mar 12, 2006 5:26 pm

Thanks for the fast response! In the previous message I accidently wrote why the reaction was happening on the oxygen side, I really meant the hydrogen side. Also, when I add table salt (iodized) it creates a brownish,yellowish substance on the oxygen side. I was wondering is the substance was iodine since the salt was iodized. Another question (sorry for so many questions) why does this reaction take place on the oxygen side?

Sorry for so many questions, I know your busy

deleted-71447 · Post by **deleted-71447** » Mon Mar 13, 2006 12:10 pm

Very interesting question. The negative electrode where hydrogen bubbles form would be attracting the positive Mg ions, so that white precipitate could be pure magnesium. There are probably some procedures you can use to test that - for example, magnesium burns at a high temperature with a very bright light. With electrolysis of table salt, I expect that the yellow-brown substance at the positive (oxygen) electrode might be chlorine gas. (I doubt you are not generating dangerous amounts, but please be aware that chlorine gas is toxic at high concentrations.) It forms when the Cl- ions are attracted to the positive charge.

deleted-71447 · Post by **deleted-71447** » Mon Mar 13, 2006 12:57 pm

Reading up on this a bit more, I found that electrolysis of NaCl solution in water does generate some chlorine gas. However, electrolysis of MgSO4 solution in water typically does not produce elemental Mg because production of H2 is more favorable.

deleted-71254 · Post by **deleted-71254** » Thu Mar 16, 2006 7:19 pm

snowfire

Can you tell you me what you are using for the electrodes? My suspician is that you are getting a reaction between the sulphate and the metal(s) in your wire.

I recommend that you use platinum electrodes.

snowfire123 · Post by **snowfire123** » Fri Mar 17, 2006 8:40 pm

I am using carbon rods (from pencil), stainless steel, and platinum for my electrodes.

deleted-71447 · Post by **deleted-71447** » Sat Mar 18, 2006 9:25 am

Have you tried the experiment with deionized water to see if you get the same precipitate? Have you tried to collect some of the precipitate and test it? For example, if it is a Mg carbonate, it will emit bubbles when mixed with hot, dilute HCL.

deleted-71254 · Post by **deleted-71254** » Sat Mar 18, 2006 4:34 pm

snowfire,

stainless steel has iron in it. iron will definately react with the suphate to form iron sulphate precipitate. It also has chromium. I'm not sure of the soluability of chromium sulphate, but it wouldn't surprise me that is also precipitates out.

Pencil lead is not pure carbon. It is a mix of graphite (carbon) and clay, a silicate. Clay is a zeolite, a natural ion exchange substrate. Thus, pencil lead may have any number of unknown ions available to chemically react in your experiment.

The platinum electrodes are your best choice.

Starting with de-ionized water is still a good idea.

snowfire123 · Post by **snowfire123** » Sun Mar 19, 2006 5:02 pm

Could it be magnesium hydroxide? (that is what my father said)

deleted-71447 · Post by **deleted-71447** » Mon Mar 20, 2006 11:28 am

Yes, magnesium hydroxide sounds like a good possibility. It is a white precipitate, similar to what you've observed. You mentioned that the precipitate occurs at the H2 electrode (the cathode), which is where hydroxide ions accumulate as H2 is produced. Likewise, the cathode attracts free positive ions like Mg, Ca, or Na. This page has some decent info:
http://www.bookrags.com/sciences/physic ... s-wop.html
This process of precipitating carbonates and hydroxides at the cathode has been used to build artificial coral reefs:
http://www.globalcoral.org/reef_restora ... awater.htm
Aragonite (CaCO3) and brucite (Mg(OH)2) are two white precipitates formed in this process of electrolysis of sea water.

If you really want to know for sure what precipitate you've got (and to impress teachers and judges), you should try to collect some and test it. It won't take very long. The "flame test" is a simple and effective method that you could use to identify calcium (red flame) versus magnesium (no color). This page has info on this and other simple lab tests to identify your compound:
http://library.thinkquest.org/2923/tests.html
Also, this page has some decent info:
http://www.broadeducation.com/htmlDemos ... s/page.htm
Figure 5 might be of special interest to you.