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Author Topic: electrolysis  (Read 6018 times)

Offline ilox

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electrolysis
« on: 28/09/2005 04:49:21 »
Hello iwas doing electrolysis on magnesium sulphate heptahydrate(epsoms salt)mixed with water, and am wondering how come i didnt get any magnesium metal, all i got was some sort of salt on the cathode? any idea what this is? You can get copper from copper sulphate so why not magnesium from mag. sulphate? I was using copper elctrodes one dissolved  into a green blue  sludge any idea what this is? Is there any way to get metals using electrolysis with aqueous solutions and without using all kinds of bizzare chemicals? Iam not a chemist!

Thanks.


 

Offline biomed0101

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Re: electrolysis
« Reply #1 on: 28/09/2005 07:36:14 »
Well, I'm not really sure, but I think that Mg is not stable enough for Mg2+ to become Mg, It has something to do with oxidation and reduction. I can remember something about redox potentials. Lat me get back to you on this topic later on.

:P
« Last Edit: 28/09/2005 07:43:17 by biomed0101 »
 

Offline daveshorts

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Re: electrolysis
« Reply #2 on: 28/09/2005 07:38:34 »
Basically it takes more energy to form Mg from Mg+ than to split water (you can tell this because if you put magnesium metal in water it will react forming hydrogen) so the water will split before the magnesium will become a metal.
 

Offline chris

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Re: electrolysis
« Reply #3 on: 30/09/2005 11:16:36 »
Dave is right. If you add magnesium to water it reacts to form magnesium ions (Mg2+), hydrogen (H2) and hydroxide ions (OH-).

So even if you did suceed in making some magnesium in your electrolyte, it would instantly react to form hydrogen !

At the cathode (negative electrode), 2 hydrogen ions (H+) accept 2 electrons and form a molecule of hydrogen gas (H2) which you see bubbling off. The other half of the water molecule (OH-) from which the hydrogen ion was derived remains in solution.

At the anode (positive electrode), copper metal donates electrons to form copper (Cu2+) ions which detach from the electrode and react with the hydroxide ions produced by your electolysis (see above) forming copper hydroxide, and with the sulphate ions from the epsom salts.

Copper hydroxide doesn't dissolve very well and forms the blue precipitate you see beneath the electrode. Copper sulphate, on the other hand, is soluble, so those ions remain dissociated and just drift around in the solution together, making it a pretty colour ! Also, depending upon the purity of the copper you used as an electrode, you will generate a pile of anode sludge comprising unreactive metals and compounds contaminating the metallic copper.

One way in which electrolysis can produce a metal product is if hydrolysis is carried out in a molten solution.

If sodium chloride (NaCl - table salt) is heated to its melting point and electrolysed it generates chlorine gas and metallic sodium. But you need to remove the sodium before it can react with the chlorine so a liquid mercury cathode is used. The sodium forms an amalgam with the mercury which is pumped out of the chamber and then mixed with water.

The sodium in the mercury reacts with the water to form sodium hydroxide, which is an important industrial raw material, and the mercury is recycled back into the electrolysis chamber.

I wouldn't, however, recommend trying this at home !

Chris

"I never forget a face, but in your case I'll make an exception"
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Offline ilox

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Re: electrolysis
« Reply #4 on: 01/10/2005 02:56:32 »
so is the copper hydroxide mixed in with the sulphate, what would this be called? copper hydroxide sulphate?

Thanks for the info.
 

Offline rosy

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Re: electrolysis
« Reply #5 on: 01/10/2005 08:43:54 »
Boringly enough, I think it would just be a mixture of copper sulphate and copper hydroxide solutions...
 

Offline blob

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Re: electrolysis
« Reply #6 on: 10/11/2005 11:52:37 »
hiya
could anyone help me with my problem plz![?] i need 2 find the melting point of sand (silicon dioxide )- SiO2
plz help ;) or else [xx(]
luv ya us 2 in science!![:X] plz dont tel ne 1 we have been on this [}:)] [:I]
 bibi for now!;)
 

Offline blob

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Re: electrolysis
« Reply #7 on: 10/11/2005 12:02:55 »
I óż Jess
[:X]
 

Offline blob

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Re: electrolysis
« Reply #8 on: 10/11/2005 12:04:43 »


I luv Jess
[:X]
[/quote][/b]
 

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Re: electrolysis
« Reply #8 on: 10/11/2005 12:04:43 »

 

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