sodiumsulfate - 27-6-2012 at 11:18
I made a batch of sodium aluminate by mixing sodium hydroxide solution with pure aluminum pellets. I added an excess of aluminum just to make sure all
the sodium hydroxide was gone. Once done I added a copper sulfate solution to it and got a dark bluish green solid. However I saw this on wikipedia
and worried this might effect my results.
"Sodium aluminate is also formed by the action of sodium hydroxide on elemental aluminium which is an amphoteric metal. The reaction is sometimes
written as:
2 Al + 2 NaOH + 2 H2O → 2 NaAlO2 + 3 H2
however the species produced in solution is likely to contain the [Al(OH)4]− ion or perhaps the [Al(H2O)2(OH)4]"
So I was concerned that I made copper hydroxide instead of copper aluminate. As a test I know I can heat the hydroxide and see if it turns to black
copper oxide. But I don't know what will happen if I heat copper aluminate. What should I do to make sure I made copper aluminate?
blogfast25 - 27-6-2012 at 12:08
Whether copper aluminate can be prepared via the ‘wet route’ depends largely on the solubility products (K<sub>s</sub> values) of both
copper hydroxide and copper aluminate. If Cu(OH)2 is more insoluble than ‘Cu(Al(OH)4)2’) then copper hydroxide will precipitate, rather than
copper aluminate. Personally I’m fairly sure that is what happened.
One way of finding out is by washing your precipitate extensively, till the filtrate runs more or less neutral. Then dissolve it in a minimum of
strong acid like HCl. If the compound is copper aluminate it will hydrolyse to Cu2+ and dissolved Al3+. Then, adding strong ammonia will cause the
copper to complex to a deep blue copper/ammonia complex and the Al will precipitate as Al(OH)3.nH2O.
Copper aluminate can almost certainly only be made (if AT ALL) by fusing alumina and CuO and even then what results may not even be one single
compound only…
NaAl(OH)4 describes the actual molecular structure of sodium aluminate better than 'NaAlO2'.
[Edited on 27-6-2012 by blogfast25]
daragh8008 - 27-6-2012 at 13:19
There is two different copper aluminates. One where the Cu is in the +2 state which is a spinel phase compound the other where th cu is in the +1
state and is a delafossite Layered compound. Neither as far as I'm aware can be made in solution at atmospheric pressure. A hydrothermal reactor
operating around 300c can be used. In this process CuCl is reacted with NaAlO2 to give NaCl and CuAlO2. the easiest method to produce either is by
solid state reactions with finely ground and mixed oxide starting material. Below 1000c the spinel phase firms while above 1050 the delafossite phase
forms.