The hexaqua ion is (Cr(H20)6)3+
This can be oxidised by the air to (Cr(H20)6)2+ solution. This can be reversed by adding Zn/HCl
If NaOH, NH3 or NaCO3 is added to the hexaqua ion then (Cr(H20)3(OH)3) ppt is formed
If excess OH- is added to this (Cr(OH)4(H20)2)2- solution is formed
If excess ammonia is added instead then (Cr(NH3)6)3+ is formed
If H202/OH- is added to the hexaqua ion then (Cr04)2- is formed. This reaction can be reversed by adding Zn/HCl
This can then be changed into (cr207)2- solution by adding H+. This reaction can be reversed by adding OH-.
This can the be converted back into the hexaqua ion by adding Fe3+
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