If i'm testing for Iron (III) in a solution, should i add NaOH of Iron III Chloride to test for brown ppt. ?

Question

If i'm testing for Iron (III) in a solution, should i add NaOH of Iron III Chloride to test for brown ppt. ?

Answer 1

Dunno, depends what else you think might be in the solution.  NaOH will precipitate many (most, in fact) transition metal ions, and Fe(III) is not the only one that will give you a brown colour when it happens.  If you know your choices are "there either is Fe(III) or there isn't anything", then your test should work.  If you think there might be, e.g. Mn(II), then a dark precipitate just means you ppt'd a metal salt, not necessarily iron, and if you precipitate seven different oxide/hydroxide salts with different colours, picking out the ferric salt won't be conclusive.

The classic qualitative test for aqueous Fe(III) is to add thiocyanate.  The [Fe(H2O)5(SCN)]2+ complex is bright blood red.

Answer 2

Yes, you can.