iron(II)同iron(III)

Add separately sodium hydroxide (or ammonia solution) to each of the two solutions.

Iron(II) solution (a pale green solution):
A dirty green precipitate is formed.
Fe2+(aq) + 2OH-(aq) → Fe(OH)2(s)

Iron(III) solution (a yellowish brown solution):
A brown precipitate is formed.
Fe3+(aq) + 3OH-(aq) → Fe(OH)3(s)

2008-05-31 22:08:54 補充：
綠色溶液可能含有Fe^2+ 離子或 Cr^3+ 離子。而黃色溶液可能含有 Fe^3+ 離子、CrO4^2- 離子、溴或碘。因此，不能單靠顏色而判定這是鐵(II)離子或鐵(III)離子。

Iron(II):
Test it with KMnO4, Fe2+ will be oxidized to Fe3+(brown).

Iron(III):
Fe3+ is brown in colour. It does not present in the 2 solutions.

綠色係iron(II)，黃色係iron(III)
因為
iron(II) ions 係綠色
iron (III) ions係黃色