Final answer:
The higher the pH, the higher the solubility of insoluble ionic hydroxides because the decreased concentration of hydronium ions in a basic solution shifts the equilibrium, favoring the dissolution of ionic hydroxides.
Step-by-step explanation:
For insoluble ionic hydroxides, the higher the pH, the higher the solubility of the ionic hydroxide. This is because as the pH increases, the concentration of hydronium ions [H3O+] decreases, leading to less protonation of the anions derived from weak acids. Consequently, the reaction in equation (16.4.1), where the anion A- reacts with water to produce hydroxide ions OH- and its conjugate acid HA, is shifted to the right, according to Le Chatelier's principle, enhancing the solubility of the ionic hydroxide.
This enhanced solubility is particularly evident for anions that are the conjugate bases of weak acids because they readily react with water to increase ph. Conversely, the presence of a strong acid would increase the hydronium ion concentration, thereby increasing the reaction with anions to form HA and reducing their solubility. Thus, in an acidic environment (lower pH), the solubility of an ionic hydroxide such as Mg (OH)2 would be increased as more Mg (OH)2 would dissolve to restore equilibrium.