Question

How does pH affect solubility?

Answer 1

Hint: The dependence of pH on solubility is opposite, or inversely proportional to each other, and it can be explained by the Le Chatelier's Principle of equilibrium.

Complete answer:
In order to answer the question, let us first know about pH. pH refers to the potential of hydrogen. We know that acid has a lot of hydrogen ion content and $pH=-\log [{{H}^{+}}]$, so lesser the pH of a substance, more acidic the substance is. Let us take an example of Le Chatelier's Principle, and use sparingly soluble salts, in order to answer our question. Let us take an example of zinc hydroxide which is a sparingly soluble base. The dissociation occurs as:
\[Zn{{(OH)}_{2}}\rightleftharpoons Z{{n}^{2+}}(aq)+2O{{H}^{-}}(aq)\]
Now, if we add more $O{{H}^{-}}$ ions which is in the product side then equilibrium will shift to the left, according to the principle and it will favour backward reaction, and as a result the solubility will decrease. This is when we increase the pH of the solution.
Now, let's decrease the pH of the solution. We add ${{H}_{3}}{{O}^{+}}$ions into the solution, which will increase the pH. Now, these ions will react with $O{{H}^{-}}$ions in the product side and form water. In the process, the $O{{H}^{-}}$ ions get removed from the solution. As the product is getting removed so according to the Le Chatelier's Principle, the equilibrium will shift to the right and forward reaction will be preferred. So, the solubility of the base increases.
So, from the above case, we can infer to the conclusion that on increasing the pH, the solubility decreases and as we decrease the pH, the solubility increases.

Note:
Apart from pH, solubility is also affected by other factors such as temperature. Temperature affects both the solubility and alters the pH.