making magnesium

[MDJH]

Hi, I was thinking of trying electroplating at home. From what I recall from chemistry back in high school, electroplating is like the voltaic cell, except that voltage is applied to reverse the direction of the reaction, plating the more reactive metal onto an electrode, while corroding the less reactive one.

 

More specifically, I was considering electroplating magnesium from epsom salt, and using one close to it on the activity series (like aluminum) so as to save on electricity use while doing it. The problem is, I only have access to magnesium sulfate, not magnesium, so I can't use a magnesium electrode. And I don't know how to get access to sulfates of ANY metals I see on Wikipedia's table of the activity series, let alone aluminum sulfate itself, though I do have access to aluminum metal. So this raises a few questions:

 

1. Do the two metal cation solutions need to have the same anion for an electrochemical cell to work? (ie. if I had the electron-donor electrode dipped in a solution with the same metal as its electrode but with an anion other than sulfate in this case, would it still function?)

 

2. For a salt bridge, would any electrolytic solution do, or are there specific rules for what solution can be used? (ie. different cation and/or same anion, etc...)

 

3. For the electron-recipient/cation-recipient electrode (ie. the one I'm looking to electroplate onto) would it need to have the same metal as the cation in solution (such as a magnesium electrode in this case) or would an inert electrode (like graphite) work too? (ie. could magnesium be electroplated onto a graphite surface from magnesium sulfate?)

 

EDIT: And if not, where could I find access to enough magnesium to function as an electrode to be electroplated onto?

[John Cuthber]

You can't electroplate magnesium from a solution in water; it's too reactive.

[MDJH]

You can't electroplate magnesium from a solution in water; it's too reactive.

Hmm? This page says magnesium reacts with acids, not water. And this page says magnesium chloride electrolysis yields magnesium... or is it different for magnesium sulfate? If not, what else would be different about it?

 

And in any case, how else could I make magnesium metal?

[Melvin]

Well, electrolysis of pure, molten magnesium chloride gives you metallic magnesium. (MgCl2 MP 714C at wikipedia). This isn't really practical or safe to be done at home, especially since Mg is not too hard to find.

 

A solution of magnesium chloride will just give you hydrogen at the cathode and chlorine/small amounts of oxygen at the anode. The Mg will not be reduced to metal, but simply converted to magnesium hydroxide, which precipitates. If you use the sulfate instead, you'll get only oxygen at the anode and hydrogen at the cathode. Plus, the hydroxide will not form since neither the magnesium or the sulfate ions are affected.

 

By the way, magnesium does react with water. It's just slow. I placed a small amount of clean Mg wire into some water and you could see small bubbles of hydrogen forming (slowly).

 

Since my dad is a welder, he can get Mg welding wire. I use that as my source (although I don't really use it very often).

Edited September 2, 2009 by Melvin
more info

[Theophrastus]

Hmm? This page says magnesium reacts with acids' date=' not water. And this page says magnesium chloride electrolysis yields magnesium... or is it different for magnesium sulfate? If not, what else would be different about it?

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Well, magnesium does react with water, just not so quickly at room temperature. For example, if you heat the metal well enough, then drop it in water- it will react. If you use hot steam, and channel it over magnesium metal, the two will react. (*for both* and pretty damn vigorously I might add)

[MDJH]

Well, electrolysis of pure, molten magnesium chloride gives you metallic magnesium. (MgCl2 MP 714C at wikipedia). This isn't really practical or safe to be done at home, especially since Mg is not too hard to find.

 

A solution of magnesium chloride will just give you hydrogen at the cathode and chlorine/small amounts of oxygen at the anode. The Mg will not be reduced to metal, but simply converted to magnesium hydroxide, which precipitates. If you use the sulfate instead, you'll get only oxygen at the anode and hydrogen at the cathode. Plus, the hydroxide will not form since neither the magnesium or the sulfate ions are affected.

 

By the way, magnesium does react with water. It's just slow. I placed a small amount of clean Mg wire into some water and you could see small bubbles of hydrogen forming (slowly).

 

Since my dad is a welder, he can get Mg welding wire. I use that as my source (although I don't really use it very often).

Thanks again, I thought it worked for aqueous electrolysis too, I guess I got the wrong impression.

 

As for the bit about hydrogen and oxygen, I saw your post in my water electrolysis thread, and I'm guessing I could expect the hydrogen and oxygen yielded by water electrolysis, when epsom salt is the electrolyte, to be pure?

[hermanntrude]

basically, at the anode, whatever can be oxidised easiest will be oxidised. At the cathode, whatever can be reduced easiest will be reduced. If the metal you're trying to reduce is stable enough as a salt, it'll stay that way and the water will be reduced instead

[MDJH]

basically, at the anode, whatever can be oxidised easiest will be oxidised. At the cathode, whatever can be reduced easiest will be reduced. If the metal you're trying to reduce is stable enough as a salt, it'll stay that way and the water will be reduced instead

 

Ah ok. So the less stable the salt, the more likely the aqueous electrolyte will be electrolyzed, and the more stable the salt, the less likely the aqueous electrolyte will be electrolyzed... so for purer hydrogen/oxygen yields, go for the more stable salts.

 

The irony is, I've changed my mind about electroplating magnesium (EDIT: more like "changed my mind about trying to electropate it") and have decided to go for using epsom salt as an electrolyte for water electrolysis instead; see my electrolysis thread. Hey that rhymes. XD

 

But yeah, this thread is now about making magnesium. How do I change the subjectline of the initial post?

[hermanntrude]

I changed the thread title for you. is that OK?

[MDJH]

I changed the thread title for you. is that OK?

Well, technically this was intended to shift to being about making magnesium metal by ANY means, since "electrolysis" only applies to molten electrolysis.

 

Thanks for changing the thread title anyway, though.

[hermanntrude]

OK so there were three posts here which belonged in the thread about electrolysis of water. I moved them. Please try to stay on topic, especially if there is a perfect thread already available.

 

As for making magnesium, my thread on making sodium "no you CAN'T make sodium" is probably pretty similar in tone to what i'd write about magnesium. The only difference is magnesium isn't quite as dangerous as sodium, and probably slightly easier to make, but not much.