[LHM]

Which of these ions is predicted to produce the most acidic solution when dissolved in H₂O?

A) K⁺
B) Ba²⁺
C) Co²⁺
D) Fe ³⁺

The answer is D, but why would Fe³⁺(aq) produce a more acidic solution than Co²⁺(aq)?

[Fluorine]

An acidic solution contains a lot of H⁺ and minimal of OH^-, right? Let's think what happens when you have these cations in water. The equation, essentially, would follow;

H₂O + Mⁿ   M(OH)_n + H⁺
or
H⁺ + OH^- + Mⁿ   M(OH)_n + H⁺

where M is representative for the listed cations and n is their charge number, respectively. Co⁺² would form Co(OH)₂ and Fe⁺³ would form Fe(OH)₃, the cobalt leaving 2H⁺ and the iron leaving 3H⁺.