Chemical Forums
Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: _Espard_ on May 17, 2014, 07:38:13 AM
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Are there any transition metal ions that still exist as free ions in solution at alkaline pH?
I imagine most form some sort of oxide or hydroxide.
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Define "free ion".
Does CrO42- count?
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Are there any transition metal ions that still exist as free ions in solution at alkaline pH?
I imagine most form some sort of oxide or hydroxide.
No. The "free" ions are always hydrated by molecules of solvent forming aqua-complex. By increasing pH, the aqua complex is usualy hydrolyzed to some sord of hydroxide or oxide as you said.
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I have another question:
Say for instance that you have two Cu(II) compounds: Cu(II) nitrate and Cu(II) acetate. You make solutions of both - the nitrate should be acidic and the acetate solution should be basic.
Upon addition of KOH to Cu(II) nitrate, you should form some amount of Cu(OH)2 which is insoluble.
Is Cu(OH)2 formed in the Cu(II) acetate solution since it is basic + there are hydroxide ions in solution? Or are the acetate ligands bound to the Cu(II) center and prevent hydrolysis?
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I have another question:
Say for instance that you have two Cu(II) compounds: Cu(II) nitrate and Cu(II) acetate. You make solutions of both - the nitrate should be acidic and the acetate solution should be basic.
Why do you believe this is so? It might be, but generally, transition metal salts are slightly acidic, and the salt of a weak base and strong acid are acidic. Now, nitric acid is stronger than acetic acid, but still ... basic?
Upon addition of KOH to Cu(II) nitrate, you should form some amount of Cu(OH)2 which is insoluble.
Correct.
Is Cu(OH)2 formed in the Cu(II) acetate solution since it is basic + there are hydroxide ions in solution?
No, such a weakly basic solution (if it forms, as I said above) isn't a base, in the Arrhenius definition (as you've used it,) but instead is Lewis base. Contrast these two definitions:
http://en.wikipedia.org/wiki/Arrhenius_base#Arrhenius_definition
http://en.wikipedia.org/wiki/Br%C3%B8nsted%E2%80%93Lowry_acid%E2%80%93base_theory
Or are the acetate ligands bound to the Cu(II) center and prevent hydrolysis?
In solution, then yes.
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I understand what you mean in regards to the acidity/basicity. I thought I read that the natural pH of a Cu(II) acetate solution was basic, but now I am having trouble find the source of that information.
Either way, if the solution is acidic, what would happen upon the addition of KOH to bring the solution up to a pH = 8, 9, or 10? Should there be substitution of the acetate ligands with hydroxide as the pH increases? I assume maybe formation constants would be applicable here.
(Just as a note, I am better trained as an organic chemist and am just now breaking into inorganic chemistry due to work so I am a bit behind on the "general knowledge" since it has been some time for me!)