Sciencemadness Discussion Board

Getting CuSO4 from MgSO4 via. Electrolysis

InFormation - 17-1-2011 at 19:04

This is going to be kind of annoying, so bear with me -

I recently got a great chemistry prac. experiments book, mainly for refining hands on skills. I need CuSO4 to do one of the experiments on recrystallization (I know, I could probably just use something else, but CuSO4 is used in a couple of the other experiments too). Now, I'd easily go out and buy some for myself, but try as I may I cannot find any CuSO4 containing products anywhere. At all. What I do have, though, is Epsom salts. What I don't have is sulfuric acid, which I'd gladly use to convert that excess Cu(OH)2 to CuSO4. I really don't feel like buying a car battery, and again, I can't find any products containing relatively pure H2SO4 for the life of me.

If it's easier, think of this as a thought experiment:
- I'd like to make CuSO4 using MgSO4 electrolysed on copper electrodes.
- I want to produce CuSO4 without it getting converted into Cu(OH)2.

Is there a way I can do this, or does anybody else have a suggested method toward CuSO4 I'm not aware of?

[Edited on 18-1-2011 by InFormation]

[Edited on 18-1-2011 by InFormation]

bbartlog - 18-1-2011 at 08:38

You can do this with a divided cell. Stainless steel cathode, copper pipe anode, MgSO4 solution, and some sort of membrane (I have used a terra cotta flowerpot, but it's both inefficient and tends to contaminate the solution with Fe). The anode solution will become enriched in CuSO4 over time.
Separating the CuSO4 from the remaining MgSO4, though... not sure how I'd go about that.

hissingnoise - 18-1-2011 at 09:00

Quote: Originally posted by InFormation  
Now, I'd easily go out and buy some for myself, but try as I may I cannot find any CuSO4 containing products anywhere.

Horticulturalists use CuSO4 against plant fungi and blights in "Bordeaux Mixture" which is essentially CuSO4 and Ca(OH)2 . . .
Garden centres should have it!

The WiZard is In - 18-1-2011 at 09:36

Quote: Originally posted by InFormation  
I need CuSO4 to do one of the experiments on recrystallization (I know, I could probably just use something else, but CuSO4 is used in a couple of the other experiments too). Now, I'd easily go out and buy some for myself, but try as I may I cannot find any CuSO4 containing products anywhere. At all. find any products containing relatively pure H2SO4 for the life of me.



Try a plumbing store or home center copper sulphate is sold as Root Destroyer.

H2SO4 try drain cleaner, or an auto supply store - battery electrolyte.

The drain cleaner is a lot stronger.


djh
----
Who remembers a SL of moons ago... town employees
out in a rowboat on the lake shoveling copper sulphate over the
side... to kill algae.

[Edited on 18-1-2011 by The WiZard is In]

peach - 18-1-2011 at 10:05

You can harvest yourself some really clean sulphuric from a lead acid battery refill pack - it's about 34% off the top of my head. You can boil that down to produce concentrated acid, but the volume will drop to about a third of what you start with.

If you scroll down here to "3 ways to make copper sulphate", you'll see nurd rage has stuck a video up with a number of different options

You may want to go with the dilute sulphuric and coil of wire one at the end if you're low on materials - the peroxide and nitric methods obviously need you to have more things to hand.

Rather than use a battery, you could use an adjustable wall plug power supply. You will want it to be DC. It would also be good if it says 'current limited' on it, as you can overload a lot of them and they'll stop working.

If you run these reactions for long enough, and have an excess of copper present, the sulphuric will disappear as it'll all be converted to the metal sulphate.

Are you in the UK?

[Edited on 18-1-2011 by peach]

bbartlog - 18-1-2011 at 14:15

Quote:
in "Bordeaux Mixture" which is essentially CuSO4 and Ca(OH)2


I have a couple of canisters of Bordeaux powder, and I think it wouldn't be that easy to get the CuSO4 out. Problem is that it's designed to undergo metathesis reaction on being mixed with water, so that it forms CaSO4 and Cu(OH)2 in a fine slurry. And I can't think of any trivial solvent extraction that would dissolve out one of the components and leave the other behind, so that would leave mechanical separation... seems hard.

InFormation - 18-1-2011 at 15:28

Thanks for all the helpful suggestions :).

@ bbartlog: That looks like the go. How exactly does the divided cell option work - do I need something electrically conductive, or slightly solution permeable? Extracting the MgSO4 left over from the CuSO4 shouldn't be hard - a methylated spirits solvent extraction should get *most* of it out, though methanol would work even better.

@ hissingnoise: I'll keep that in mind, if I can figure a way to extract the two.

@ The WiZard is In & peach: I tried looking for both CuSO4 and H2SO4 in all their common products: root killer, lead-acid refill kits, drain cleaner. I couldn't actually find any root killer; the LE refills were a solution of Cadmium sulfate instead, and I don't remember what was in the drain cleaner. Maybe they just don't use H2SO4 in commercial cleaning solutions much in this part of Australia? Thanks for the suggestions anyway.

I'll have another look at the hardware, maybe I just missed a thing or two.

[Edited on 18-1-2011 by InFormation]

starman - 18-1-2011 at 15:52

Copper sulfate available fairly pure in the garden aisle at bunnings.The only OTC source of H2SO4 in Australia I have been able to locate is "low fume" pool acid at a limited number of pool suppliers.Drain cleaners in Australia all seem to be hydroxide,and I've yet to see electrolyte replacement at any auto shop.

InFormation - 18-1-2011 at 16:14

Quote: Originally posted by starman  
Copper sulfate available fairly pure in the garden aisle at bunnings.The only OTC source of H2SO4 in Australia I have been able to locate is "low fume" pool acid at a limited number of pool suppliers.Drain cleaners in Australia all seem to be hydroxide,and I've yet to see electrolyte replacement at any auto shop.


Yeah, that's pretty much the situation. The only place I didn't check in Bunnings was the garden section! (tried gardening in K-Mart and they didn't stock any CuSO4 root killer). I'll be sure to keep my eyes open for the low-fume pool acid from now on. Thanks for the tip!

peach - 19-1-2011 at 04:45

I don't often see refill packs on the shelves here in the UK either.

It's quite likely they keep them behind the counter or elsewhere, or only offer to do the refills for you, in a lot of places.

Have a look online in your area first. If that fails, try calling the local garages.

You may have more luck getting the acid if you take your chemistry book along and show them what you're thinking of doing - if they ask.

With the coil of wire method, I'd use the dilute acid. Dilute acid is just sulphuric mixed with more water. There's not much point concentrating the acid (which is annoying and potentially dangerous) to then dilute it back down.

froot - 19-1-2011 at 07:18

I've been looking at something that may be able to help.

http://en.wikipedia.org/wiki/Daniell_cell
Quote:
This variant, called a gravity cell, consisted of a glass jar in which a copper cathode sat on the bottom and a zinc anode was suspended beneath the rim in the zinc sulfate layer. Copper sulfate crystals would be scattered around the cathode and the jar would then be filled with distilled water. As the current was drawn, a layer of zinc sulfate solution would form at the top around the anode. This top layer was kept separate from the bottom copper sulfate layer by its lower density and by the polarity of the cell. A disadvantage of the gravity cell was that a current had to be continually drawn to keep the two solutions from mixing by diffusion, so it was unsuitable for intermittent use. In addition, it was vulnerable to loss of integrity if too much electric current was drawn, which would also cause the layers to mix.


Maybe you could employ this concept to get clean CuSO4 by substituting the Zinc electrode with Mg?

[Edited on 19-1-2011 by froot]

indigofuzzy - 19-1-2011 at 08:46

I have actually made a large amount of CuSO4 by electrolysis of MgSO4. My setup was as follows:

Take a one gallon glass jar with a wide mouth. (Wide enough for a 2 liter soda bottle to fit into). Pour a two pound bag of epsom salt into the jar, and fill most of the way with distilled water. Stir vigorously until all of the MgSO4 dissolves.

Cut the bottom off of a two liter soda bottle, and rinse the bottle thoroughly. Bunch up a coffee filter over the mouth of the bottle, and secure with a few rubber bands.

Take scrap pieces of copper and twist them together to make the anode. Twist the bare end of an insulated copper wire around the bundle of scrap copper. Drop this into the bottom of the jar with the insulated copper wire hanging out.

Now insert the soda bottle into the jug mouth first, but do not submerge it so far that solution spills over the top.

Place a piece of stainless steel, another scrap of copper, or any old piece of relatively non-reactive scrap metal (preferably clean scrap metal) into the open end of the soda bottle.

Connect the insulated copper wire to the positive end of a 12V power supply. Connect the piece of scrap metal to the negative end. Watch the hydrogen bubbles fizz on the cathode. (I recommend good ventilation)

Allow this to run until the solution turns deep blue and stops getting darker (About 3 days, IIRC)
Magnesium hydroxide will collect in the soda bottle, and toward the end, some copper hydroxide also.

Hope this helps.

bquirky - 19-1-2011 at 12:57

H2SO4 can be purchaced over the counter at most chemical supply companys and most battery chains

I purchaced 2L for about $20 from sigma chemicals in Balcatta WA

InFormation - 19-1-2011 at 15:48

@ peach: Since it's so hard to come by, I was actually hoping I could use the CuSO4 I get via. means other than using H2SO4 to make good quality sulfuric acid in the future.

@ froot: That could be do-able! I suppose it depends if the CuSO4 will sink / float as opposed to just mixing homogeneously with the MgSO4.

@ indigofuzzy: You know, I might just try that. I did something similar (just a standard electrolysis, both anode and cathode same height, but on a much smaller scale) about a week ago, but most of the CuSO4 that got formed turned to Cu(OH)2. I'm guessing your setup worked in the gravity-jar way froot was suggesting.

@bquirky: I'll have a look into that. Might save me a world of trouble in the long run if it's easy to get in the first place.

This morning on a small sample I made about a week ago (heavily contaminated with MgSO4) I'm trying extraction with the small amount of MeOH in denatured alcohol. I'll let you know how it goes... (not expecting much from it).

bbartlog - 20-1-2011 at 06:11

Quote:
I'm guessing your setup worked in the gravity-jar way froot was suggesting.


No, his setup was effectively a divided cell. The coffee filters jammed into the neck of the soda bottle function as a membrane. I like the setup, cheap, crude and effective (as long as your solution doesn't destroy coffee filters). The gravity cell is neat but seems touchy... makes me wonder how stable the separation of layers is.
Quote:
I'm trying extraction with the small amount of MeOH in denatured alcohol.


Just curious... what makes you think this will work? Browsing the solubilities of copper and magnesium sulfate in alcohol(s) in one of the old books (Atherton Seidell, 1919) it looks like both salts are very slightly soluble in the anyhydrous state and somewhat moreso as hydrates, i.e. there doesn't seem to be a lot of prospect for separating the two in this way. You could try fractional crystallization, as CuSO4 is less soluble than MgSO4 in water (especially cold water). If you can get the anode solution to the the point where it is more than half CuSO4, and the solution is saturated at some warm temperature, then slowly cooling to 0C should precipitate relatively pure copper sulfate.
However it might take some doing to get the concentration of Cu++ high enough relative to Mg++ for this to work, and it would still leave most of your CuSO4 in solution, making it more like something that would be useful if you were doing a lot of batches using the same electrolyte.

InFormation - 20-1-2011 at 15:06

@ bbartlog: Makes sense it should function as a divided cell, I see now. I might just try that sometime in the near future.
And about the extraction, from what I found, the Copper(II) sulfate pentahydrate has a solubility in MeOH of about 10.4g/L @ 18degC. I'm aware that MgSO4 is also very slightly soluble in MeOH and EtOH, but I don't have access to anything other than the 5% or so MeOH in denatured alcohol. So that will have to do in terms of what I can do with solvent extraction. I like your idea better though - I did try fractional crystallization once, but the solution must have been supersaturated as the entire solution turned to crystal almost instantly, heavily contaminated with MgSO4 throughout. It did look pretty cool to have the entire beaker brick up though, so it was somewhat worth it. :)

[Edited on 20-1-2011 by InFormation]

InFormation - 22-1-2011 at 23:23

Denatured alcohol extraction is pathetic - most of what I got was the trace MgSO4 that dissolved in the EtOH. There was so little CuSO4 in the ~5% MeOH that it wasn't even visible. Ironically, I did end up finding it at the hardware store - instead of as root killer, is was for treating plants that are deficient in copper. "Warning: Use sparingly as the active constituent may burn plant matter." Thanks for all the help though!

[Edited on 23-1-2011 by InFormation]

cyanureeves - 23-1-2011 at 13:33

i'm doing that inverted bottled method right now using suede instead of coffee filter and it seems to be working pretty good.i like how the white stuff separates and goes to the cathode side,but every time i go near the bucket i get this nasty crap build up inside my nose that leaves me feeling fluish like.i had to put a box over it and run the wires through holes i made on the side of the box. i already had made some when this thread first came up but hadnt separated both salts.when this batch is done i'm thinking of using that first run and separate it.i wonder if all will go the same.

InFormation - 23-1-2011 at 20:15

Quote: Originally posted by cyanureeves  
...every time i go near the bucket i get this nasty crap build up inside my nose that leaves me feeling fluish like.i had to put a box over it and run the wires through holes i made on the side of the box.


That gas is probably hydrogen... Are you doing this in a ventilated space? Hydrogen is explosive, and can cause asphyxiation if too much of the air content is hydrogen... Might want to do it somewhere more ventilated.

cyanureeves - 24-1-2011 at 12:57

well the box took care of that nasty gas.i just gave a quick discription of the symptoms,of course its not a massive build up i can scrape out but it is something in my nostrils and sinuses somewhere for sure.i hate it,i thought it was sulfuric and could even feel a film on my lips. oh well 24hrs. on a 12volt connection and i can see some blue deposits.