Al Koholic - 24-8-2006 at 10:04
ZnSO4 is conveniently made from US pennies by reaction with H2S04 procured as battery acid replacement. One can facilitate this reaction by either
cracking the pennies to expose the Zn beneath the Cu coating or can add some H2O2 to the H2SO4 to begin dissolving Cu as well.
Anyway, I have been conducting the reaction for a while by slowly adding penny after penny as I get them in change. Just because...
I am purifying the compound and have run into some interesting observations with recrystalization and such. Recrystalization from plain water works
fine. However, the crystal size is somewhat large at times and definetly not uniform. I am attempting to make nice uniform crystals of the sort I
have observed when using organic solvents to precipitate the salt.
I did some qualitative experimenting with different solvents for crashing out the ZnSO4 and found that isopropanol works well (and is very cheap and
environmentally benign). That being the case I was very surprised when adding isopropanol to a hot saturated solution of ZnSO4 not only did not
precipitate the salt, but also PREVENTED the precipitation of the salt when the T reached room temp.
The flask separates into two layers no matter how much agitation has been done. I can't seem to break the water-salt affinity. I tried acetone as
well and this has the same effect. Any idea why this has happened? I'm going to keep working on a way to precipitate the salt. Could be an
interesting study on salt concentration v.s. amount of organic solvent required to cause precipitation.
12AX7 - 24-8-2006 at 11:25
I didn't have good luck at recrystallizing ZnSO4 (heh, I think you typed ZnS*zero*4 once there), always made a nasty solid mat of acicular crystals.
Do you mean large crystals by length or diameter? Length can of course be crushed down.
No idea why it precipitates at room temp, but after heating, won't. Is it being changed in some way? I don't see why oxidation or reduction would do
anything though... oxidation would give acetone and reduction (not easy?) could only give propane, which wouldn't even remain.
Tim
Al Koholic - 24-8-2006 at 11:36
Well, it precipitates very readily from a standard water recrystalization by letting the filtered hot saturated solution cool to room temp. In that
process I typically get some larger clumpy masses of crystal that when vacuum filtered out, get all messy into a large clump that needs to be crushed
up. No big deal admittedly...
What I was noticing though was that the liquid left in the filtration flask after separating the crystal mass (considered a saturated solution) could
have isopropanol added and this would crash out very nice, small, uniform (shape and size) crystals. These seem far superior in quality than the
crushed up mass I was getting with straight water. So I figured why not just add the alcohol to the hot saturated solution before letting it cool,
and then get the whole product in one shot as nice uniform flowing crystals.
I know it seems trivial, but I like nice neat crystals in my storage jars!!!
So letting this alcohol containing solution cool to room temp just results in 2 layers being formed and NO crystalization which normally would have
readily occured.
I could see the oxidation thing...but then you have acetone which should also be effective at crashing out the salt....
Anyway, I am now attempting to cool the flask to get precipitate. I just hope I don't get the messy crystal mass from before. There has got to be a
way to do this reliably. I have a distinct feeling that when hot, there was just too much salt dissolved in the water to allow any alcohol but a
small amount to mix in. This could have formed the 2 layers but preventing crystalization all together???
EDIT - So the cooling operation succeeded. Interestingly, this is a good method for producing VERY fine ZnSO4 crystals. I cooled the flask for about
10 minutes and noticed the formation of long thin needles at this point. I removed the flask and shook it up and stirred it thinking the needles
would seed the rest of the solution...which they did. I now have an extremely fine precipitate of very small needles of ZnSO4!!! Time for some
filtering...
[Edited on 24-8-2006 by Al Koholic]
Eclectic - 24-8-2006 at 13:26
Even NaCl will salt out half of the water from 70% isopropanol (to 88% I've read). Try ethanol or methanol to avoid separation into a water rich and
alcohol rich phase.
Rosco Bodine - 25-8-2006 at 15:41
Not to rain pennies on your parade here , but you do know that zinc sulfate is a common gardening supply item , and zinc metal ( pot metal ) scrap is
a common recycling material , as well as being the metal casing
on cheap carbon zinc batteries .
If you have trouble precipitating the usual acid salts ,
neutralize with sodium carbonate or bicarbonate and
the nearly insoluble zinc carbonate precipitates very readily . The carbonate can then be converted to whatever acid salt you wish by reacting with
the acid .
12AX7 - 25-8-2006 at 18:39
Yep, and pennies are 97.5% pure zinc (more if you don't dissolve the copper), which can't be said for potmetal (as bad as 72% Zn, and most of the
impurity is aluminum, not copper).
Tim
Rosco Bodine - 25-8-2006 at 19:16
There are anode zincs used on boats to prevent corrosion
on the propellors , and I think these are pure zinc . The larger boating supply stores will have an assortment of these anode plates , up to several
pounds in size .
Al Koholic - 27-8-2006 at 08:41
Oh yeah those are all good sources. It is doubtless one of the more common metals to run across.
The idea of the project was sort of just to put to better use, normally cluttering change. And hey, I might have a crack at making some ZnSO4 needles
and see how big I can get them now that I know how to control the precipitation well.
Also have to precipitate some Zn powder from this now too...