Bordeaux Mixture

[the guy]

I wanted to buy some Bordeaux mixture (as in the solution of copper sulfate and calcium hydroxide) so that I could precipitate the copper out of it as copper hydroxide (using sodium hydroxide).

The Bordeaux Mixture that is on sale here is in powder form, and says 'tetra copper tricalcium sulfate'.

In my head it sounds like this is just the dehydrated form, forming a complex, and that it will dissociate into the respective ions again in solution.

Since I cannot find any information to confirm or deny this, however, I would just like to ask for some confirmation before I buy it...?

Thank you in advance

[ajkoer]

Since Bordeaux mixture is prepared (see Wikipedia) from mixing solutions of copper sulfate and Ca(OH)2 or CaO, I suspect that what we have is a mixture of Cu(OH)2 and CaSO4. Now, apparently CaSO4 is very insoluble and cannot even be dissolved in HCl. So add HCl and recover a solution of CuCl2 leaving CaSO4 behind. Now add NaOH (try to avoid exposure to air and CO2):

 

CuCl2 + 2 NaoH --> NaCl2 + Cu(OH)2 (s)

 

Good luck.

 

As a side note, I would also avoid the use of any carbonates as your final product would be more likely a basic copper carbonate (Cu2(OH)2CO3, for example). Dissolving the Bordeaux mixture in ammonia water will also work by dissolving the Cu(OH)2, but an issue may surface on removing the ammonia from the copper complex. For example, adding H2O2 may react with NH3 forming a mixed nitrite salt.Source, per Wikipedia (http://en.wikipedia.org/wiki/Ammonium_nitrite ) to quote:

 

"It can also be prepared by oxidizing ammonia with ozone or hydrogen peroxide" and "Ammonium nitrite may explode at a temperature of 60–70 °C.[2] It decomposes more quickly when a concentrated solution than when it is a dry crystal."

 

As such, I would avoid ammonium nitrite and related mixed Copper salt for fear of potential extreme instability even in aqueous solutions. Using NaClO or HOCl on the copper ammonium salt to separate out a copper salt is equally problematic, very toxic and explosive side products (NH2Cl, NHCl2, NCl3, or N2H4) with the likely formation of a basic copper oxychloride. However, treating the copper ammonium complex with CaO may produce a copper salt precipitate (see http://www.jstor.org/discover/10.2307/25040124?uid=3739808&uid=2129&uid=2&uid=70&uid=4&uid=3739256&sid=21102222166897 ), but this may be CuO and only slowly formed, hence my recommended route.

Edited April 30, 2013 by ajkoer

[John Cuthber]

"but an issue may surface on removing the ammonia from the copper complex."

Unless you know enough chemistry to realise that, if you leave a solution of copper salts dissolved in ammonia to dry out the ammonia evaporates and you get left with essentially copper hydroxide.

Boiling off the ammonia achieves the same effect.

Of course, you can try oxidation with ozone if you like, but it certainly isn't the easy way to do it.

[the guy]

Actually, the reason I wanted the copper hydroxide is for the synthesis of the ammonia-copper complex.

 

So if I were to dissolve the mixture in ammonia, would it be easy to separate this from the CaSO4?