Question

Precipitation Reactions is the title of the section
the problem is A solution of sodium hydroxide is added to a solution of iron (II) chloride.

My Net ionic equation was
OH- + Fe+2 -> Fe(OH)2


I want to know if my answer is correct and why OH in Fe(OH)2 is in parentheses please explain.

Answer 1

Actually, the net ionic equation is
2 OH^- + Fe^+2 ==> Fe(OH)2
The valence (oxidation state) of Fe is +2 and that of the hydroxide ion is -1. It is the entire OH part that is -1. All compounds like Fe(OH)2 have a zero charge on them so we must have 2 of the OH pieces with -1 charge each to make -2 and that exactly balances the +2 charge on the Fe ion. The parentheses are necessary to show that the entire OH part is multiplied by 2.
Fe(OH)2 means 1 Fe and 2 OH ions. If we wrote it as FeOH2, we would have ONLY the H multiplied by 2. [Fe is +2, O is -2, and H2 is 2*1 = +2 so we end up with +2 charge for the compound which is a no, no. (It must be zero.).