My post warning above is wrong if we mean this kind of salt.
#7
Nicol76
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Thank you everyone for your help. Yes I meant salt in chemistry. Sorry Merlin, English is not my first language and I probably used the wrong word. My question is about ionic compounds.
@Nicol76 No, you were correct.
I asked "what is a salt" to check you know it as an ionic compound and so you are looking for the ions with colour green.
Coloured ions are transition metals, because of their electronic structure.
##Fe^{2+}## and ##Ni^{2+} ## are predominantly green.
Other ions which are not generally green, are green in some compounds ##Cu^{2+} ## usually blue, is green in basic copper carbonate , and ##Cr^{2+} ## changes from its usual violet to green in chromium hydroxide.
That is because the energy levels are modified by surrounding ions such as hydroxide. This is shown nicely with copper sulphate, where the ##Cu^{2+}## ions are a pleasant pale blue in the hexahydrate crystals or in aqueous solution. There the ##Cu^{2+}## are surrounded by water molecules. If excess ammonia is added to the solution, the ##Cu^{2+}## become surrounded by ##NH_3## molecules and turn a glorious deep blue.
#10
Nicol76
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just saw your reply. Thank you so much, this is really useful.