Solubility product when you add an acid to a solid? I ran into some trouble when I was resolving some exercises about solubility product principle.The exercise says: 


  A concentrated, strong acid is added to a solid mixture of $0.015\ \mathrm{mol}$ samples of $\ce{Fe(OH)2}$ and $\ce{Cu(OH)2}$ placed in $1.0\ \mathrm{L}$ of water. At what values of pH will the dissolution of each hydroxide be complete?


So, I don't know how start when you have an acid and an insoluble salt when using the Ksp equation. 

I know I can't to do this.

$\ce{Fe(OH)2 + HCl -&gt; FeCl2 + H2O}$

$\ce{Cu(OH)2 + HCl -&gt; CuCl2 + H2O}$

Not even do I have a common ion in order to establish a reaction. Do you know where I should begin? I tried using $K_\mathrm{sp}$, but I already have molar solubility, is $0.015\ \mathrm{M}$ for both. I can't ignore that. I don't find useful $K_\mathrm{sp}$ in this case. I know there's something that I'm not understanding. Hope you can help me to figure it out.
Are not you complicating the problem?

The solution is simple. You have $\pu{0.015M}$ of $\ce{Me(OH)2}$ and according to the reaction you will need twice as much acid (based on stoichiometry): $\pu{0.030M}$. Knowing that $\pu{pH = - \log [H^+]}$, the dissolution will be complete at $\pu{pH = 1.52}$.