Answer:
1. Ca(OH)₂ : Yes
Highest solubility = pH of 2
2. Cu Br : Yes
Highest solubility = pH of 4
3. Ca₃(PO₄)₂ : Yes
Highest solubility = pH of 2
Explanation:
From the common ion effect, the solubility of an ionic compound in a solution which already contains one of the ions in that compound will reduce. This is because, when an external stress is placed on a system in equilibrium, the equilibrium position will shift to remove the effect of that stress. Therefore, when more of the same ions are added to a solution already containing that ion, equilibrium will shift towards removal of the ion, thereby reducing solubility.
1. For Ca(OH)₂:
Ca(OH)₂ is a fairly soluble ionic compound whose dissociation equation is given below:
Ca(OH)₂ (s) ----> Ca²+ (aq) + 2 OH- (aq)
Increase in pH will result in addition of more OH- ions, therefore, its solubility will decrease. On the other hand, a decrease in pH will remove OH- ions, thereby increasing solubility. The pH of highest solubility is 2.
2. For CuBr:
CuBr is a slightly acidic salt as it is salt of a strong acid, HBr and a weak base Cu(OH)₂. Hydrolysis of the salt will result in an acidic medium:
2 CuBr (s) + 2 H₂O (l) ----> 2 HBr (aq) + Cu(OH)₂ (aq).
Thus, an increase in pH will result in an increase in the solubility of CuBr due to the removal of H+ ions. The highest solubility will be at pH of 4.
3) For Ca₃(PO₄)₂
Calcium phosphate is a salt of slightly basic salt as it is a salt of a weak acid, H₃PO₄ and stronger base Ca(OH)₂.
Hydrolysis of the salt will result in a basic medium:
Ca₃(PO₄)₂ (s) + 6 H₂O (l) ---> 3 Ca(OH)₂ (aq) + 2 H₃PO₄ (aq)
Therefore, its solubility increases with decrease in pH due to the removal of OH- ions. The highest solubility will be at pH of 2.
