Sciencemadness Discussion Board - How to crystallize CuCl2?

How to crystallize CuCl2?

mr.crow - 16-7-2012 at 07:42

I have 300mL of a deep green solution containing almost 1 mol of CuCl2. There is excess acid so that means tetrachlorocuprate is present

My question is how do I get this solution to crystallize? My current plan is to use an ice/salt bath to cool it off.

kristofvagyok - 16-7-2012 at 08:27

Quote: Originally posted by mr.crow

I have 300mL of a deep green solution containing almost 1 mol of CuCl2. There is excess acid so that means tetrachlorocuprate is present

Boil off most of the water.
It's molar mass is 134.45 g/mol
Solubility in water
70.6 g/100 mL (0 °C)
75.7 g/100 mL (25 °C)
107.9 g/100 mL (100 °C)

So the 300cm3 solution is too much...

mr.crow - 16-7-2012 at 18:27

Ok I boiled it down to 200mL, will see if any nice crystals form

The darkness of the solution is astounding, it looks black except for the emerald green bubbles and meniscus. It reminds me of the H2PdCl4 solution

EDIT: Crystals! The long stringy needle kind

[Edited on 17-7-2012 by mr.crow]

mr.crow - 22-7-2012 at 20:22

I have posted a followup here

Arthur Dent - 29-7-2012 at 05:14

I have made some very nice CuCl2 crystals a while ago, but I started with a very pure solution of CuCl2 that was made by slowly dissolving fine copper telephone wire (my favorite copper source) in concentrated HCl. It takes a couple of days but eventually it all dissolves and you're left with a strange-looking turbid brownish solution.

Take that solution and drop a little 9% hydrogen peroxide and magic! The solution turns a beautiful emerald green! From that point on, boiling off a good part of the water (reduce it to half) and then just letting the remaining concentrated solution crystallize off in a dessicator and you'll have very beautiful crystals... the slower it cristallizes, the nicer the crystals.

This way, by not using Copper Sulfate as your starting point, you can ensure that there won't be trace contaminations of CuSO4 in your Chloride crystals.

Robert

[Edited on 29-7-2012 by Arthur Dent]

mr.crow - 30-7-2012 at 07:35

There's a frood who really knows where his towel is

I ended up just boiling the solution then letting it cool. Lots of tiny needle like crystals spring to life. Then filter the liquid off and boil some more, etc. So no large crystals for me.

The CuSO4 actually crystallizes separately when the concentrated solution is diluted. The extra HCl must be more strongly complexing at high concentrations.