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ElectroWin
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Colour of copper (II) salts depends on pH; becoming green in more acidic conditions; and lovely deep blue in basic conditions.
[Edited on 2013-5-21 by ElectroWin]
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blogfast25
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Quote: Originally posted by ElectroWin  | Colour of copper (II) salts depends on pH; becoming green in more acidic conditions; and lovely deep blue in basic conditions.
[Edited on 2013-5-21 by ElectroWin] |
Are you sure you're not confusing with the colour of the tetrachloro cuprate anion [CuCl42-]? That is very green. Add HCl or
NaCl to CuSO4 and it turns green, more intensely with chloride concentrations. But I've seen (and made) highly acidic copper nitrate solutions as blue
as the ocean...
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woelen
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Color of copper(II) does not directly depend on pH, it depends on the nature of the ligands.
With water-ligands, the color is sky blue. You have this when you dissolve copper sulfate or copper nitrate or copper sulfamate.
When water ligands are replaced by chloride-ligands, then the color goes from blue to yellow. Mixed water/chloride complexes are green.
Copper(II) with bromide as ligands (e.g. CuBr4(2-)) gives deep purple color. Try dissolving some CuSO4.5H2O in a saturated solution of KBr or NaBr and
you'll see that color.
With ammonia ligands copper(II) has a deep royal blue color, very beautiful to see this complex.
Complexes of copper with certain ligands only exist in certain ranges of pH, e.g. the ammonia complex only exists in weakly alkaline to moderately
strongly alkaline solutions. At very high pH (> 14) it decomposes and leads to formation of copper hydroxide.
Complexes of copper with chloride or bromide only exist at low pH to neutral pH.
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blogfast25
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... which at that pH dissolves to blue cuprate [Cu(OH)42-], another ligand causing blue colour of the complexed Cu2+
ion!
[Edited on 21-5-2013 by blogfast25]
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Eddygp
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Cu(NH3)4SO4 is an amazing colour. I strongly recommend its easy synthesis just to see it.
there may be bugs in gfind
[ˌɛdidʒiˈpiː] IPA pronunciation for my Username |
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