Is it easier to oxidise $\ce{Fe^2+}$ to $\ce{Fe^3+}$ in acidic or alkaline solution?
$$ \begin{align} \ce{Fe &-> Fe^2+(aq) -> Fe^3+(aq)}\\ \ce{Fe &-> Fe(OH)2 -> Fe(OH)3} \end{align} $$
In my textbook it is written that as soon as $\ce{Fe^{2+}}$ changes to $\ce{Fe^{3+}}$, it acquires $\ce{OH-}$ to form $\ce{Fe(OH)3}$. This promotes oxidation of $\ce{Fe^{2+}}$ changes to $\ce{Fe^{3+}}$. I don't quite get this why precipitate formation speeds up the reaction?