Sciencemadness Discussion Board

Purifying Copper Sulphate

Reflux-and-Chill - 14-6-2016 at 08:15

I am wondering what would be the most efficient (and not overly complicated) way to purify 200g of CuSO4·5H2O... I was thinking recrystallization, but maybe there is some better way. It would be great if you could write a quick guide. Thank you.

aga - 14-6-2016 at 08:32

Recrystallisation is THE way.

Maybe 2 or 3 times, depending on your skill, and how pure you need it to be.

Edit:

Both purity and skill increase after three recrystallisations.

[Edited on 14-6-2016 by aga]

Reflux-and-Chill - 14-6-2016 at 08:43

Would you be so kind as to teach me the best way to recrystallize it? My skill level is currently quite low (but it's not the worst) and I'm interested in leveling up.

aga - 14-6-2016 at 09:18

I'm by no means an expert, but here goes :-

Recrystallisation sounds quite easy, however the exact execution of the process can be tricky.

Fore-warned is fore-armed, so use a solubility table to see what is going to happen, e.g. : https://en.wikipedia.org/wiki/Solubility_table

That table says that CuSO4.5H2O (copper sulphate pentahydrate, which is probably what you have) will dissolve in water, and 27.5g will dissolve in 100 ml water @ 20C, yet 114g will dissolve in 100ml water at 100C.

Pick a vessel to do your recrystallisation in.

If it's a standard 250ml beaker, you can safely hold 200ml of water in it.

Now we have some data and can do a bit of maths : 200ml water.
The solubility table says 114g in 100 mls of water @100C, so you're going to need to weigh out exactly 228g of your impure crystals.

Wrong. They're impure so take a guess and add one or two grammes more.
(with this particular recrystallisation, you don't actually have to weigh it at all, but it is good practice to do so.)

Heat the 200ml of distilled water to boiling point - it will be at about 100C, so no need for a thermometer for this particular process.

Start adding your 230g of impure crystals, with stirring. Wait for the last crystals to fully dissolve before adding the next lot.

Repeat until you have added all the crystals, OR the last crystals simply will not dissolve. If you added them all and they all dissolved, you will need to add more, which is an indication that the estimate of impurities was wrong.

When your solution will not dissolve any more copper sulphate, it is certainly saturated, which is what we wanted in the first place.

While the liquid is hot, filter it. This removes any larger impurities, like dust, bugs, trees, elephants etc.

Now you will have a hot, clear, saturated copper sulphate solution.

Just leave it to cool - better to wait than to force it to cool in a fridge.

As it cools, the solvent (water in this case) cannot hold 114g per 100ml anymore, so the copper sulphate has nowhere to go - it must crystallise.

We started with crystals and we're getting purer crystals, hence the term 're-crystallisation'.

Slow cooling actually forms purer crystals : http://www.ce.gxnu.edu.cn/organic/net_course/content/Crystal...

Crystals can form instantly or take days to appear. With copper sulphate, you should see some after 24 hours at the most (if you did it right).

Now some Art : you have to Judge when you have enough crystals, or you think no more will form, then pour off the solvent that sits above the crystals.

The solvent contains the impurities, which is why you discard it.

This is why recrystallisation is a trade-off between how much product you get and how pure it is - you always lose some in this process.

You can chill your solvent to extract a 'second crop' of crystals or even a third, however you'll also be adding back in more impurities.

Give it a go, and please report back with photographs, weights, volumes etc.

I'll get some started as well : we can compare results when you post your photos.

[Edited on 14-6-2016 by aga]

elementcollector1 - 14-6-2016 at 09:19

1) Add just a little water, not enough to dissolve the crystals. This can be tricky to judge, as CuSO4 is slow to dissolve, but use Wikipedia's solubility guidelines for this.
2) Heat solution to boiling. The rest of the crystals should dissolve.
3) Let cool. Crystals will begin precipitating, growing larger as the solution cools back to room temperature. Slower cooling means bigger and more pure crystals.

EDIT: I actually needed something to do on my few days off, so excuse me while I go try this.

[Edited on 6-14-2016 by elementcollector1]

aga - 14-6-2016 at 09:28

nice one elementcollector1 !

Please hold off posting results until Reflux-and-Chill gets a chance to try it out at least twice - first time it may all screw up, so have some patience.

Edit:

I screwed up the maths by forgetting the .5H2O already in the crystals.

It won't all fit in a 250ml beaker !

Start with 125ml water and recalculate accordingly.

[Edited on 14-6-2016 by aga]

Reflux-and-Chill - 14-6-2016 at 10:00

THANK YOU for such great replies! I have a little bit more work to do and then I'm all over this project. I'll post the results when it's done.

DO NOT DISTURB

Armistice19 - 14-6-2016 at 11:16

From experience I can tell you that IMHO the most important thing here is not to disturb the copper sulfate solution during cooling in any way, shape, or form! Put it somewhere up high, in an isolated area where there is very little opportunity for vibration or air current, and of course make sure not to poke at it!

aga - 14-6-2016 at 13:02

Quote: Originally posted by Reflux-and-Chill  
then I'm all over this project. I'll post the results when it's done.

Be sure that you do !

I've already got mine weighed, photographed, dissolved, filtered and is recrystallising as i type.

You got a week before i auto-post my results, photos, yields etc. Hopefully elementcollector1 will give you the same grace period.

The 'active' part is at most 3 hours. The rest is basically waiting.

DJF90 - 14-6-2016 at 13:51

There is a sentence in a book that I've read that has stuck with me to this day, and it goes a little something like this:
Quote:
There is no point in trying to purify a material if you cannot assess the improvement in purity that the process has afforded


What this means is that without some means to show that the purity has been improved, there is no point in trying to purify. Back in the old days this may have been "recrystallise to constant melting point". Whilst I do not wish to discourage any efforts to recrystallise the copper sulfate, what makes you so sure it needs purifying in the first place? Unfortunately with inorganic compounds a melting point (range) is rarely indicative, but perhaps you may attempt some gravimetric or titrometric analysis of the "impure" material and after a single recrystallisation in order to determine what improvement (if any) has been acheived.

[Edited on 14-6-2016 by DJF90]

j_sum1 - 14-6-2016 at 14:46

My last attempt at this...
:)

aga - 14-6-2016 at 15:08

This is basically a very simple DOING project.

Please, oh please, let someone Do something for a change.

CharlieA - 14-6-2016 at 17:11

Quote: Originally posted by DJF90  
There is a sentence in a book that I've read that has stuck with me to this day, and it goes a little something like this:
Quote:
There is no point in trying to purify a material if you cannot assess the improvement in purity that the process has afforded


What this means is that without some means to show that the purity has been improved, there is no point in trying to purify. Back in the old days this may have been "recrystallise to constant melting point". Whilst I do not wish to discourage any efforts to recrystallise the copper sulfate, what makes you so sure it needs purifying in the first place? Unfortunately with inorganic compounds a melting point (range) is rarely indicative, but perhaps you may attempt some gravimetric or titrometric analysis of the "impure" material and after a single recrystallisation in order to determine what improvement (if any) has been acheived.

[Edited on 14-6-2016 by DJF90]


Excellent, professional advice! I would suggest determining Cu by titration with a standard carbonate solution. Alternatively, sulfate could be determined gravimetrically as barium sulfate.

j_sum1 - 14-6-2016 at 17:27

Quote: Originally posted by DJF90  
There is a sentence in a book that I've read that has stuck with me to this day, and it goes a little something like this:
Quote:
There is no point in trying to purify a material if you cannot assess the improvement in purity that the process has afforded


What this means is that without some means to show that the purity has been improved, there is no point in trying to purify. Back in the old days this may have been "recrystallise to constant melting point". Whilst I do not wish to discourage any efforts to recrystallise the copper sulfate, what makes you so sure it needs purifying in the first place? Unfortunately with inorganic compounds a melting point (range) is rarely indicative, but perhaps you may attempt some gravimetric or titrometric analysis of the "impure" material and after a single recrystallisation in order to determine what improvement (if any) has been acheived.

[Edited on 14-6-2016 by DJF90]

I agree with this sentiment entirely which is why I do not feel the need to recrystallise what I have. (Besides, the lab is out of action.) I have pottery grade copper sulfate that I have no reason to suspect is impure.

That said, there is a "just in case" mentality that one might apply. If there was some impurity present then recrystallisation would be a way of getting rid of most of it.
Also one way to assess purity is to compare the purified crystals visually with the discarded crud. If there is any sign of the crud being discoloured or some notable difference in the crystals then you can be reasonably certain that some impurities have accumulated there.

But I think it is possible to overstate the importance of purity in an amateur lab setting. The last chemplayer video I watched had a bug crawling inside his beaker. Maybe some bug parts made their way to the product but I am guessing that they filtered out at a later step.

macckone - 14-6-2016 at 19:44

With really pure copper sulfate you can get huge perfect crystals. Impurities disrupt the crystal formation resulting in smaller crystals with less regular structure. Pottery grade is seldom the best purity but is usually sufficient for a home lab. Maybe we could have a crystal growing contest.

Reflux-and-Chill - 14-6-2016 at 21:07

For those wondering why I am interested in purifying it; it's because it was cheap to buy, and the person told me that it's not the purest sample.
And come on, crystallization is cool and you know it.

[Edited on 15-6-2016 by Reflux-and-Chill]

j_sum1 - 14-6-2016 at 21:44

Quote: Originally posted by Reflux-and-Chill  
For those wondering why I am interested in purifying it; it's because it was cheap to buy, and the person told me that it's not the purest sample.
And come on, crystallization is cool and you know it.

[Edited on 15-6-2016 by Reflux-and-Chill]

And that's a good enough reason to attempt it.


After you have had a go, maybe you could organise a competition as per mackone's suggestion.

Reflux-and-Chill - 14-6-2016 at 23:00

That sounds good.

NEMO-Chemistry - 15-6-2016 at 05:29

Ok count me in! Discard everything i said about copper sulphate crystals in other threads :D. I am making my copper sulphate as i want to use up some conc nitric acid. If nothing else i am bound to have impure stuff if i am making it :D.

Great idea for a competition to improve skills.

Cabalaba - 15-6-2016 at 09:47

I made a nice inch long Cu(II)SO4 crystal as described above, then rinsing the residue with ethanol (it's insoluble in EtOH), repeating again. Then forgot about the solution in the freezer. Some crystals were larger but couldn't be recovered since the mass had to be broken.

I'll try to post a pic when I get home.

Actually recrystallization is an important technique, partly if you're trying to salt out a product how made, though eve then there are other ways of approaching fast.

However, without an expensive machine or if you have a special technique to detect impurities, you won't know how "pure" it is.

Cabalaba - 15-6-2016 at 09:49

One more point if you have a pure sample crystal, it can be used as a seed

Reflux-and-Chill - 15-6-2016 at 10:42

I would like to learn using pure sample crystals as seeds.
P.S. UPDATE: They are growing nicely.

NEMO-Chemistry - 16-6-2016 at 07:34

Looks like i can start tomorrow evening, so for various reasons i would like to go a slightly different route! I am just checking i am on the right track.

I have some conc nitric acid (more than i am happy having), the bottle is clear and says 68% but dosnt fume much when opened. Its a Amazon buy so not too sure if the 68% is true or not, what i am think is murder a few birds with one stone.

So take Nitric and add same volume of water (distilled), i will decide and measure the amount tomorrow but i am thinking roughly 200ml Acid and 200ml water.

I have some copper wire left over from a loft extension, so i intend to weigh portions of copper and add to the acid until no more dissolves. maybe while heating to around 30-40C?

the idea is too get some copper nitrate plus from the left over copper nitrate i can add sodium carbonate? This should give me basic copper carbonate? The sodium carbonate is fairly pure according to the container but it dosnt seem anhydrous, so i will just add until no more reacts.

take some of the copper carbonate and add sulphuric acid until no more reaction to give me copper sulphate? Then purify the copper sulphate by recapitalization.

Does this sound ok? The reason for going this route is to add some more reagents to my collection and to use up some conc nitric Acid. As i am not 100% sure of the concentrations and water contents of what i have, i will weigh the amounts of what add as i go. Does this sound ok? Or am i missing something that is going to make this fail?

I also need to do this in the shed so when the copper is dissolving in the nitric Acid is sodium carbonate in a wash bottle ok to neutralize any NOx gas given off? i will blow the NOx through the set up with a small air pump. Comments welcome.

edit i might actually start with more acid or use some Magnesium carbonate as well, i dont have any magnesium nitrate so that is another i could make.

aga - 16-6-2016 at 07:46

Too complicated.

Better to just make some copper sulphate from your sulphuric acid with electrolysis.

Nitric acid is less of a worry than conc sulphuric !

Edit:

Also, Reflux-and-Chill has had plenty of time to boil 125ml of water, add/dissolve crystals, filter, leave to cool ...

... so will probably post his results pretty soon ... ?

[Edited on 16-6-2016 by aga]

Reflux-and-Chill - 16-6-2016 at 08:30

I see that you're subtly and politely telling me that it's time to post the results, with which I agree. I think the crystals are looking pretty good at this point. Let me just dry them and snap a few pics, and I'll be back in no time.

Here they are:

Reflux-and-Chill - 16-6-2016 at 08:35



Before.jpg - 862kB After.jpg - 721kB

NEMO-Chemistry - 16-6-2016 at 08:37

Quote: Originally posted by aga  
Too complicated.

Better to just make some copper sulphate from your sulphuric acid with electrolysis.

Nitric acid is less of a worry than conc sulphuric !

Edit:

Also, Reflux-and-Chill has had plenty of time to boil 125ml of water, add/dissolve crystals, filter, leave to cool ...

... so will probably post his results pretty soon ... ?

[Edited on 16-6-2016 by aga]


Nitric acid is a paranoia thing now we are not meant to have it. Apart from being complicated do you see any reason it wont work?

I know he is posting his results but still good practice to do any way. AND I get to add to my reagents :D.

Reflux-and-Chill - 16-6-2016 at 08:50

Neither nitric nor sulphuric acid have to represent a major concern if handled and stored with care. SAFETY FIRST, people!

NEMO-Chemistry - 16-6-2016 at 08:53

Quote: Originally posted by Reflux-and-Chill  
Neither nitric nor sulphuric acid have to represent a major concern if handled and stored with care. SAFETY FIRST, people!


Conc Nitric isnt legal for the public in the UK :(, i misread the Amazon advert and got two, lots of two litres each by mistake! It was worded in a way that sloppy reading made me think i was getting 2 ltr total.

Reflux-and-Chill - 16-6-2016 at 09:00

How many liters did you end up receiving?

NEMO-Chemistry - 16-6-2016 at 09:25

Quote: Originally posted by Reflux-and-Chill  
How many liters did you end up receiving?


4 Ltr, the advert said 1ltr bottle packaging, i missed the bit about it being for 2 bottles! The advert used a different company bottle as the picture.

But the acid is clear and seems ok, dosnt fume and dosnt have any orange in it, which i thought a bit odd for 68%. Anyway its way more than i will use in a reasonable time frame and conc sulphuric is allowed so easy to get at the moment.

I probally prefer to have nitrate salts rather than nitric acid, then i can make the acid as i need it, i will keep 1-2 LTR conc anyway.

If i go electrolysis then i have to clean battery carbon rods and likely to get an even more impure product, plus wet chemistry seems a bit quicker.

I normally use an extension lead for electric to the shed, so thats one reason i am sort of confined to weekend chemistry for anything needing electric or anything that requires a bit of time.

Also i would like some copper compounds anyway. I am half way through trying to make a dry glove box for copper nitrate crystals.

I was tempted to flush the box with propane but instead will use sodium hydroxide for the desiccator. Hopefully if i put the everything including the final storage bottle in, i might be able to get some fairly dry copper nitrate crystals.

Cool crystals by the way.

aga - 16-6-2016 at 09:29

Woohoo ! Well done Reflux-and-Chill !

That works out at a yield of 82%, which is pretty close to the 84% i ended up with, although that is probably because i started with 5x as much 'dirty' crystals.

start.JPG - 132kB filter.JPG - 176kB gunk.JPG - 146kB precip.JPG - 159kB crystals.JPG - 196kB drying.JPG - 157kB

Reflux-and-Chill - 16-6-2016 at 09:42

Fuming nitric acid is a solution that contains more than 86% nitric acid, so don't worry about the lack of fumes. If you want to find out the concentration, you could titrate it against a known concentration of Sodium Hydroxide using a simple indicator like Phenolphthalein.

Thanks.

Reflux-and-Chill - 16-6-2016 at 09:43

WOW, aga! That looks awesome!!! It seems that you did great job with this.

NEMO-Chemistry - 16-6-2016 at 09:49

Wow, how many crystallization did you do? definitely a skill worth developing, i wasnt expecting to see so much crap on the filter paper.

Copper salts have a great colour dont they.

So my target is around the 80% mark, how long did they take to crystallize? I hope to have it done and dusted by 8pm Sunday night.

[Edited on 16-6-2016 by NEMO-Chemistry]

aga - 16-6-2016 at 11:13

It's just one recrystallisation, although my cock-up with the .5H2O meant that it would not all fit in one 250ml beaker.

The photo of the crystals drying is the second portion, with the already-dried 'main' portion in the container behind it (container=1 litre disposable drinks cup).

The process with copper sulphate is easy enough to describe in just a few words, without pictures.

The photos are really just to show that it was actually done rather than just photograph two piles of the same crystals.

As can be seen in the photo of the filtration step, crystals have already formed : copper sulphate doesn't hang around much when recrystallising due to the solvent losing heat.

By the morning you will get a large crop of small crystals, usually fused into a single lump, which is why it's best to use plastic containers in this step : you'can't squeeze glass.

[Edited on 16-6-2016 by aga]

Reflux-and-Chill - 16-6-2016 at 11:44

It was actually done, but I can see why you would think these are two piles of the same crystals (they do look very similar). The second pile are in fact the recrystallized crystals that I filtered out of my beaker. I know they are, because what else could they be? This is my first time doing this and you don't need to be so passive-aggressive, just because my crystals look like crap compared to yours. Thank you.

DJF90 - 16-6-2016 at 12:12

Quote: Originally posted by aga  

By the morning you will get a large crop of small crystals, usually fused into a single lump, which is why it's best to use plastic containers in this step : you'can't squeeze glass.

This is why (process) chemists use stirring when (re)crystallising compounds.

aga - 16-6-2016 at 12:17

Quote: Originally posted by DJF90  

This is why (process) chemists use stirring when (re)crystallising compounds.

What ! they want even smaller crystals !

Makes sense i suppose : they're likely going to dissolve and use them straight away.

aga - 16-6-2016 at 12:20

Quote: Originally posted by Reflux-and-Chill  
It was actually done, but I can see why you would think these are two piles of the same crystals

It is what it is.

The photos i posted show what the process looks like, and may be of some use to somebody one day.

Yes, there is a lot of crap in the filter.

[Edited on 16-6-2016 by aga]

aga - 16-6-2016 at 12:30

Quote: Originally posted by Reflux-and-Chill  
my crystals look like crap compared to yours

They don't: yours look much better, much more professional.

DJF90 - 16-6-2016 at 12:50

Quote: Originally posted by aga  
Quote: Originally posted by DJF90  

This is why (process) chemists use stirring when (re)crystallising compounds.

What ! they want even smaller crystals !

Makes sense i suppose : they're likely going to dissolve and use them straight away.


Not necessarily smaller crystals, but it helps give a narrower particle size distribution and greatly improves handling properties compared to large crystalline chunks. Suspensions of the crystals in the mother liquors have to be pumped through transfer lines from the reaction vessel to the filter unit. In addition, any subsequent use of the product (whether used in another reaction on scale, or sold/used as a reagent/substrate/building block/pharmaceutical) will benefit from the improved handling and dissolution properties that the smaller crystalline solids will possess (in comparison to having to grind/mill/dissolve larger chunks of solid material).

The only reason a chemist would perform crystallisation without agitation would be for the purposes of growing an aesthetically appealing crystal specimen or for preparation of a single crystal suitable for X-ray diffraction experiments (structure determination).

EDIT: One caveat to using agitation - mag stirring will return a (finely) ground solid due to action of the stirrer bar. Best use mechanical stirring.

[Edited on 16-6-2016 by DJF90]

elementcollector1 - 16-6-2016 at 22:13

I'm going for a big ol' single crystal of CuSO4, so I'll probably pop back in a few days or a week from now with my own pics. Wasn't concentrating on yield, but it looks about right. : P

Reflux-and-Chill - 17-6-2016 at 04:23

Quote: Originally posted by aga  
Quote: Originally posted by Reflux-and-Chill  
my crystals look like crap compared to yours

They don't: yours look much better, much more professional.

aga, y u trollin' so much?

NEMO-Chemistry - 17-6-2016 at 14:33

Quote: Originally posted by Reflux-and-Chill  
Quote: Originally posted by aga  
Quote: Originally posted by Reflux-and-Chill  
my crystals look like crap compared to yours

They don't: yours look much better, much more professional.

aga, y u trollin' so much?


Out of interest makes you think he is trolling? Not being funny i guess i didnt interpret his reply the way you did. The net is a funny thing and its hard to read peoples intent of word without a facial expression to accompany the words.

Also i get the feeling some/alot of the older members (time wise) are pretty mistrustful of newer members, but then again this is mainly chemistry based site so you need to use caution with questions until they know you i spose.

I think there has been 'kewles' etal on here previously (a kewel i believe is a druggy????). Any way nice crystals and i think you misread what he was saying.

One last thing dont take things to heart, at the end of the day aga did the experiment also, he has some experience and the way he presented his information was good.

Us newbies can learn from this and when i post mine up at the weekend i will try and follow a similar write up. Lats be brutal here, two piles of crystals show you did the crystallization, but agas gave more information by providing a pictorial reference.

I admit not easy to photo things when your busy doing, but as a newbie i was surprised to see so much crud on the paper, now when i do mine i am expecting more but now i wont think its abnormal to get so much.

I am not being critical of you, i just think sometimes it helps to step back and see the bigger picture.

I kinda promised in another thread i wasnt going to do copper sulphate crystals!! Bah looks like thats gone out the window :D.

But better to practice on cheapo copper sulphate than hard won crystals from a plant extraction :D. Only got to chop the copper wire today, but weekend is lab time!!

aga - 17-6-2016 at 14:45

People tend to do better if they treat Honestly with other People, virtual or otherwise.

'Better' as in learn more.

Reflux-and-Chill - 17-6-2016 at 23:40

I think I got it; the second pile of crystals never dissolved, and the ones that did never recrystallized...but not like that matters anymore. This has been very educational. Thank you all for your help and time, farewell!

myristicinaldehyde - 29-6-2016 at 13:08

Tried this myself, but got smaller crystals than I hoped. Next time, cover the beaker!

image.jpeg - 1.8MB

MrHomeScientist - 30-6-2016 at 11:37

Going back to DJF90's remark about purity:
Quote:
There is no point in trying to purify a material if you cannot assess the improvement in purity that the process has afforded

I know at the amateur level it's difficult to specify the exact purity of a substance (99% vs 99.9%), but in my experience with copper sulfate at least there is a pretty clear improvement visually. When dissolving 'root killer' grade hardware store copper sulfate, there is always a green/brown residue that remains and refuses to dissolve. Whatever this is would contaminate reactions, so is worth my time to remove with at least one recrystallization. This results in clean, pure blue, well-formed crystals that clearly appear a good deal more pure. Not even considering the beauty of the process!

While I agree with your statement up to a point (doing 17 recrystallizations with no way of measuring the improvement is pointless), I do believe at least one recrystallization is always warranted. It certainly can't hurt, and you know it will always increase purity to some extent.

experimental - 16-7-2017 at 02:42

Recently I bought 1 Kg of technical grade copper sulfate, which turned out to be quite dirty. Just dissolving some in water left a sand-like deposit on the bottom of the flask, so I decided to recrystallize it.

I did the same procedure that aga explained in this thread, but had to work in batches of 200 g each and to dry the crystals I used a buchner funnel.
After each batch the glass frit of the buchner was visibly dirty, so I washed it with some hydrochloric acid.

Everything went well, but the saturated solution of CuSO4 where the crystals formed accumulated after each batch and I was left with nearly 600 mL.

CuSO4.jpg - 115kB

So I tried to make a second crop, evaporated 200 mL of it down to about 75 mL (when a crust of crystals started to form on the surface) and left it to cool, without any hot filtration this time.

And here is where the problems started: the next day I found dual-colored crystal in the beaker! Most of the crystals were the usual color of CuSO4, but a smaller amount of lighter colored crystals were also present.

CuSO4-2.jpg - 74kB

Can any of you guess what happened and how to recover more copper sulfate in such a situation? My explanation is that some hydrochloric acid remained in the glass frit and in subsequent batches I somehow made copper chloride.

confused (Mg:Cu sulphate separation/re-crystalization)

Sulaiman - 16-7-2017 at 07:43

The resurrection of this thread made me consider, just as an exercise,
re-crystalizing some solutions that I used for electrochemical cell (primary batteries) experiments,
both are presently saturated at c15 oC
. copper sulphate solution that is contaminated with an unknown ammount of magnesium sulphate
. magnesium sulphate solution that is contaminated with an unknown ammount of copper sulphate.

Although I have done re-crystalizations before I did not think about it much, I just followed a procedure.

Why would only the desired compound crystalize out ?
............................................................................
Solubility curves for MgSO4.7H2O and CuSO4.5H2O for reference, if needed.
Notice the curve for magnesium sulphate ... I'll think about that later :)

Attachment: Cu_Mg_SO4.ods (19kB)
This file has been downloaded 380 times
Attachment: Cu_MgSO4.xls (10kB)
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Cu_Mg_SO4.jpg - 101kB

EDIT:
MgSO4.5H2O is a known substance, so to my simple mind, Mg and Cu could even form a double-salt / co-crystal / quasicrystal, why not ?

[Edited on 16-7-2017 by Sulaiman]

experimental - 30-7-2017 at 15:19

Ok, I found a solution to the mixed copper sulfate and copper chloride crystals. Just added some distilled water and a small amount of sulphuric acid.
Then boiled the water like in an ordinary recrystallization, and the more volatile hydrochloric acid evaporated.
The recrystallized crystals were uniform in color, thus only copper sulfate remained, but probably with some H2SO4 contamination despite washing them with cold water.

XeonTheMGPony - 31-7-2017 at 07:14

If you want pure Copper sulfate for a test make it!


H2SO4 + 35% H2O2 + Copper

use a container that is much larger then the acid peroxide charge as this will foam and spew out Ozone, so do out side or in a good fume extraction system, it will warm up plenty on its own as well.

You do not need a whole lot of peroxide either as it seems to behave like a catalyst in this reaction.

I used 50ml concentrated H2SO4 to 25ml of H2O2 then just dumped copper in till it stopped reacting, then I added 10ml more H2O2 and heated the solution till no more copper would react (I used excess copper, so the H2SO4 was my limiting reagent)

let cool to room temp then placed in the freezer, filtered the solution in a paper filter then air dried then warmed to semi dehydrate them to ensure any trace of the peroxide was decomposed. got a nice bottle of pure copper sulfate for testing my hydrazine sulfate with.

AJKOER - 10-8-2017 at 05:52

Per Wikipedia (https://en.m.wikipedia.org/wiki/Copper(II)_sulfate ), the copper(ll) sulfate pentahydrate is, to quote:

"soluble in methanol[1]
10.4 g/L (18 °C)
insoluble in ethanol, insoluble in acetone"

So dissolve the copper(ll) sulfate pentahydrate in a sufficiently large volume of CH3OH, and most other possibe impurities (MgSO4, FeSO4,...) should precipitate out.

Decant and just let evaporate or apply heat.

This simply method does show, per precipitates, a rough idea of the level of impurities, which can be further measured. Unfortunately, it requires a 100 ml of methanol for each gram of the pentahydrate. One could do a few grams at a time only, and reuse the CH3OH, which is recaptured by distillation.

[Edit] Per another source (see https://pubchem.ncbi.nlm.nih.gov/compound/Copper_II__sulfate... ):

from HSDB
1 g in 3 ml glycerine
Osol, A. (ed.). Remington's Pharmaceutical Sciences. 16th ed. Easton, Pennsylvania: Mack Publishing Co., 1980., p. 748

from HSDB
15.6 g/100 cc methanol @ 18 deg C
Weast, R.C. (ed.) Handbook of Chemistry and Physics, 68th ed. Boca Raton, Florida: CRC Press Inc., 1987-1988., p. B-90

[Edited on 10-8-2017 by AJKOER]

18thTimeLucky - 19-8-2017 at 10:19

I guess I am late to the crystal growing competition from last year?
I just started using ScienceMadness yesterday and decided to make an account today and I couldn't resist to post some pictures of a copper sulfate crystal I have been growing since January 2017 as my first post.
This thread seems to have been semi-resurrected so I hope I can please atleast one person with some blue beauty! (its mass is 46g)
It has some smaller crystals growing out of it because I am an idiot and recently replaced the copper sulfate solution but I was not thinking and used hot water so when it cooled down I got crystals everywhere as you can imagine, maybe I thought I was doing a recrystallisation or something...
If anybody is interested in my process, just ask! I have plenty of pictures from almost every month since I have started growing it.
I hope this isn't too different from the thread which is more aimed at purifying copper sulfate by recrystallisation.

(and yes that is an upside down curry paste jar, no expense is spared for you guys)

IMG_7162[1].JPG - 1.5MB IMG_7164[1].JPG - 1.4MB

[Edited on 19-8-2017 by 18thTimeLucky?]

experimental - 20-8-2017 at 10:44

That is an impressive crystal, well done 18thTimeLucky?

In my case I'm just purifying some technical grade copper sulfate that contained a lot of impurities. The sulphuric acid solution got the job done, but the next time I'll try dissolving it in methanol.

18thTimeLucky - 20-8-2017 at 23:35

Quote: Originally posted by experimental  
That is an impressive crystal, well done 18thTimeLucky?

In my case I'm just purifying some technical grade copper sulfate that contained a lot of impurities. The sulphuric acid solution got the job done, but the next time I'll try dissolving it in methanol.


Thanks!
Although methanol does seem like a good solvent to use because of the insolubility of possible contaminants, 10.4g/L is a pretty miserable solubility.
Unless you have several litres of methanol and recover the methanol afterwards then it hardly seems worth the bother.
If you only had a few grams or below of copper sulfate you needed to purify for a reaction then maybe it would be worth it.

Also thats good to know the sulfuric acid solution got the job done, I will try that for when I decide to purify a 500g bag of impure 99% copper sulfate I have been meaning to get round to!

experimental - 21-8-2017 at 14:19

Yeah, didn't notice the 10.4g/L figure. Not that "soluble" actually.

As for sulphuric acid, please consider my case was as follows.
The main method for purifyng copper sulfate I've used is recrystallization. However, after doing several small batches and washing the buchner with HCl to remove the leftover impurities, some HCl remained in the filtrate.

When I decided to recrystallize a second crop from that filtrate to increase the yield, I got crystals of copper chloride mixed with the desired copper sulfate crystals. This is where sulphuric acid came to the rescue.