Sciencemadness Discussion Board - Copper Sulphate: impurity, decomposition?

Copper Sulphate: impurity, decomposition?

jgourlay - 9-7-2008 at 12:51

I bought some copper sulfate off ebay. Now, before you write me off as an r'tard, please understand that I haven't been able to find it at the local hardware store. Probably because I don't know the alternative use. I asked for "root killer" and they keep directing me towards some polymeric goo in a spray can.

In any case, I get my little zip lock of ebay copper sulfate, and I dissolve in Rev. Osm. water. The point is crystals for the kid--and I understand not to let him suck on them like rock candy.

PRIOR to the copper sulfate coming out of solution, I get this precipitate that is GREEN, and of a dust like consistency--it's not something that will crystallize.

Once the copper sulfate crystallized out, I drove it to almost dry by evaporation. Then I poured off all the water and "washed" the coppersulfate with water--and did so thoroughly knowing I would lose some blue in the hopes of getting off the green. At this point I was assuming the green was some form of impurity/additive. I also assume (incorrectly?) that the resulting crystals should be pure.

On to the next solution whose intent is to produce crystals for the boy. Success with the crystals--but again, this green precipitate coming out first, and in about the same quantity as the first time.

So...now I'm thinking a) some decomposition product? b) a reaction caused by the water picking up some chrome/iron from the boiling pot c) something else? I've also noticed that the longer I let a copper sulphate solution sit around, without evap, the more of this I get. Do you all know what this is?

12AX7 - 9-7-2008 at 13:08

Powdery precipitate, that would be something like copper hydroxide, or if there's a lot of chloride (which there must be if it's green), copper oxychloride.

Add a little acid to prevent decomposition. I don't think I've ever had to, though. Maybe you've got something weird in there. After recrystallizing a few times, you should have a pure blue substance that doesn't decompose.

Basic ions in the water could do that, but you've more or less ruled that out with the RO. Now, when you say chrome/iron in the pot, what exactly are you implying the pot is made of? No metallic pot will suffice, you must use a metal more noble than copper (including copper, silver, gold, etc., most of which I'm guessing you don't cook with), or glass or plastic.

If it is emerald green, Cr2O3 (or from solution, Cr(OH)3) would do that, but I wouldn't expect to see that precipitate. Fe(OH)3 is brown and would show up on sitting, as the solution oxidizes (which is an excellent way to remove Fe from solution).

Tim

UnintentionalChaos - 9-7-2008 at 14:10

Hmmmm....what department did you ask about root killer? I've always seen it right next to the drain cleaners in plumbing, but am increasingly finding one of those magical 0.001% active ingredient products. Is it possible that the seller knows squat about chemistry and sent you the wrong compound? What do the crystals that form look like? Copper sulfate should be bright blue, and more or less like this http://www.crystalgrowing.com/labgrown/cuso4_xx.jpg A picture of the crude product could be helpful. The good way to go about recrystallizating this would be to dissolve as much CuSO4 as possible in a fixed amount of water at boiling, add maybe a little less than 10% more boiling water for a time delay (so crystals don't clog the funnel before the solution gets through), filter through cotton balls lightly packed into the stem of a funnel (if the solution is cloudy or has this powdery gunk), then cool, perhaps in the fridge (make sure you don't spill it).

I have never had CuSO4 decompose while boiling and I have never needed to add any acid. It is likely an impurity or the wrong compound.

[Edited on 7-9-08 by UnintentionalChaos]

jgourlay - 9-7-2008 at 15:09

Thanks for the replies gents. Coupla things:

1. RO--this is from our household water filtration system, which supposed to be an RO system but which also hasn't been changed out since the clinton administration.

2. Pot: stainless steel pot. Not that I am NOT boiling the solution in the pot. My wife would have my nuts for that. I'm boiling the water, then pouring it over the copper sulfate.

3. It is copper sulfate. I used to grow these when I was a kid, back when you could actually buy this stuff at the pharmacy, I recognize it. It also looks just like the pretty picture.

Root killer: I'm asking whichever non-english-speaking-mouth-breather I encounter in the store. Like you, I'm seeing more and more of these next-to-nothing-in-it products.

UnintentionalChaos - 9-7-2008 at 15:40

1: buy a few gallons of distilled water. It'll cost all of a dollar or two, last quite a few experiments, and you can be sure it isn't a problem with the water.

2: You can do this in the microwave in a glass jar or heavy plastic container that can withstand boiling (HDPE or PP). I've never had CuSO4 attack stainless, but it will if there is any chloride around.

I'd give it a shot again with the above recommendations and see what happens. If you isolate the possible problems to only the copper sulfate itself by removing water and vessel as potential sources and still have it forming, it is probably some sort of decomposition or impurity.

jgourlay - 9-7-2008 at 15:57

Thanks! I'll get some different water and try that. FYI, I DID try it in the microwave, only I got a little distracted.

Let's just say I'm REAL glad I had a couple of hours to clean all the blue splatters out before the wife and kids got back from shopping!

I've now got a $5 garage sale microwave (from my wife) and have been instructed that that is the microwave in which I may 1. try to smelt iron (not so successful) 2. make plasma (works well!) 3. fry CD's 4. etc!

YT2095 - 10-7-2008 at 01:23

there`s nothing wrong with buying off eBay, I bought 2250g of quick dissolve copper sulphate off there for quite a reasonable price too, it`s Technical grade and I also had the same effects that you did.

the dissolved calcium in tap water will be responsible for much of the green ppt, I`v found that adding a few drops of sulphuric acid to the soln, and letting it settle for a while and then carefully filtering it off works quite well.
and I`v grown some large crystals from this too.
but the great part is that once you`v done all this you`ll not have to do it again if you use distilled water as your crystals are now already quite pure.

the purity of the stuff I bought was 99.5%, it`s not Bad, but there will be "Strange" bits in it at first.

ScienceSquirrel - 10-7-2008 at 03:23

I have bought some copper sulphate from eBay in the past that clearly had whitish bits among the blue crystals.
After a couple of recrystallisations from deionised water I obtained some brilliant blue crystals.
The mother liquor from the first recrystallisation has a greenish cast.
I assume that some of the chemicals sold on eBay are technical grade at best and require a bit of cleaning up before they can be used.

jgourlay - 10-7-2008 at 06:11

You probably got yours from the same source I got mine.

franklyn - 10-7-2008 at 15:59

Commom Copper (cupric) sulfate pentahydrate is available as a pond algecide
http://www.amazon.com/Sanco-Chemicals-Crystal-Copper-Sulfate...

.

I think I know what the impurity is....

jgourlay - 19-9-2008 at 05:49

I think the impurity is a copper oxide. My reasoning for this is that in the yard, after the hurricane, I found an old piece of copper that had been lying in a pot for a while. It had the same green verdi-gris cast the impurity does.

Pulverized and put into water, this copper oxide has the same behaviour as well.

If this is the case, could I "clear up" my copper sulphate by adding some sulphuric acid to the solution? Would that convert the oxide to the sulphate?

What I'm doing now is crystallizing out the copper sulphate. But it's turned into tough sledding as the proportion of the "green grunge" to copper sulphate has become such that the green grunge settles on the hanging crystal now.

At each redissolution of the sediment, the stuff at the bottom looks less and less like copper sulphate with some green impurity and more and more (in fact EXACTLY) like a deposit of malachite with azurite.

blogfast25 - 19-9-2008 at 06:13

jgourlay:

The verdi-gris substance is in all likelihood not oxide but copper hydroxycarbonate, Cu2CO3(OH)2, occurring in nature as the copper mineral and ore Malachite. It's what give copper exposed to weathering its typical lime green patina, seen so often on copper cupolas and other exposed copper objects.

Copper (I) oxide (Cu2O) is red, copper (II) oxide (CuO) black.

Copper has this tendency to form these hydroxy thingymejibs, notably with carbonate, sulphate and chloride. They are insoluble and probably the source of your sulphate woes...

12AX7 - 19-9-2008 at 06:31

Of course, that would imply either excess sulfate in solution, which would rapidly reach equilibrium in the parts-per-thousand range (CuSO4 pH ~ 4?). So either you have a volatile acid (HCl? HOAc?) evaporating or a volatile base (NH3? NaOH aerosol?) dissolving. Sulfuric acid stays in solution.

Tim

jgourlay - 19-9-2008 at 06:57

blogfast: geez....

So...basically I'm left with what I've got an there's no remediation except this slow process?

What about a dilute solution of the mix--that should take up the copper sulfate, followed by filtration?

DJF90 - 19-9-2008 at 12:20

Surely adding some more dilute sulphuric acid will do the trick, and then recrystallise from that solution, and wash the crystals with water to remove as much of the acid as possible. Some acid will be left in the crystal structure but this is the case if you start from copper oxde, and can be remedied (supposedly) by recrystallising again.

SlushY!!!!

jgourlay - 23-9-2008 at 06:20

I got impatient yesterday morning. I reasoned that since solubility was a function of temperature, the thing do to was to decrease the temperature.

I EXPECTED to get one of three results. Either no change (aka vodka), a large crystal in a block of ice (aka ice cubes from hard water), or a block of ice with a bubble of copper sulphate sludge in the middle (freezing sugar water).

What I got was......behind door #4. It was a solid block of a frozen turquoise copper sulphate and water slurry. Upon thawing, it turned into a turquoise emulsion. After settling over night the solution was greenish, and the turquoise sludge on the bottom appeared to be sliver sized anhydrous copper sulfate. My seed crystal was about 3 times the size of when I'd put it in, and still hanging by its thread.

Interestingly, the solution after nuking didn't turn the expected cobalt blue, but instead turned an inky blue-green. I plunked the seed crystal back in, sped off to the mine, and am anxious to see what I see when I come back.

blogfast25 - 23-9-2008 at 06:42

BTW, jgourlay, your 'Safe or stupid' thread has been moved to here and is causing a bit of debate... lol.

undead_alchemist - 23-9-2008 at 10:16

Just for the sake of making copper sulphate, I have made about 1kg from scratch.
I just used copper wire and sulphuric acid, left it on low boil for day or so, then drain off the acid.
Just used tap water, added it to the wire and oxide mix, let settle, filter and boil down to half.
Then let it cool, end up with very bight blue crystals of copper sulphate each time.

Yes, I know that may not be the best way to make it, but it works and I was bored at work...

jgourlay - 13-10-2008 at 08:11

Quote:

Originally posted by DJF90
Surely adding some more dilute sulphuric acid will do the trick, and then recrystallise from that solution, and wash the crystals with water to remove as much of the acid as possible. Some acid will be left in the crystal structure but this is the case if you start from copper oxde, and can be remedied (supposedly) by recrystallising again.

Okay gents, a further update. I took the solution with some of the muck in it and put it through vacuum filtration. Some points, then a question.

1. It filtered out enough of the muck that I could no longer see ANY muck in the solution.
2. The muck is copper colored. It looked green sitting in the blue copper sulphate solution. But in the harsh light of day, it's copper colored.
3. I dried it, scraped it off the filter into a little water, and started adding H2SO4 drop by drop and at one point it all seemed to suddenly dissolve and the solution turned pale blue. Note that what was also present were some small CuSO4 crystals that had also filtered out.

Now....what do you think the copper colored stuff was, and do you think the addition of the acid made it into CuSO4?

Now, remember that I filtered. So I then had a nice deep blue and very clean (appearing) soln. of CUSO4. Now, many many days later, the green grunge is back in the bottom, and lots of it. So whatever the hell this stuff is, it's being "made" by the CuSO4 solution itself.

If you all think it that the answer to the above question is "Yes", then the solution to my trouble is as was suggested above: add acid and recrystallize. I've been hesitating at this point only because I have a good litre of solution and it's sitting on the window sill over the kitchen sink (wife alert).

Last issue. I'm kind of tired of mucking about with this. What's the fastest way to get all the CuSO4 out of solution? At this point, my son understands that the blue stuff makes pretty crystals, and I want to get the blue stuff out of solution and into a jar as fast as possible and evaporation is taking way too long. Is there something I can add that will make the CuSO4 suddenly all precipitate out?

I'm anxious to move on to the purple stuff....

Formatik - 13-10-2008 at 15:37

You can precipitate CuSO4 from solution by shaking with ethanol or acetone.

12AX7 - 13-10-2008 at 16:19

Cu2O? I've made what looked like tabluar crystals of copper, but weren't quite shiny enough, more of a matte finish, and quite brittle. This was the result of an acidic CuCl2 + NaCl + HCl solution inbetween regular kitchen paper towel (to dry the crystalline precipitate collected, which was probably cyan CuCl2 and green CuNa2Cl4).

Tim