Final answer:
The solubility of PbSO4 decreases with the addition of SO4^2− ions due to Le Chatelier's Principle causing a shift in equilibrium and precipitation of PbSO4 from the solution.
Step-by-step explanation:
The solubility of PbSO4 (lead(II) sulfate) decreases with the addition of SO42− ions. Adding sulfate ions to the solution where PbSO4 is in equilibrium will increase the concentration of these ions in the solution. According to Le Chatelier's Principle, this will shift the equilibrium to the left, resulting in the precipitation of more PbSO4 to reduce the stress on the system, thereby decreasing its solubility.
The addition of a strong acid like HCl may not significantly affect the solubility of PbSO4 because the corresponding acid of sulfate ion, HSO4−, is relatively strong with a pKa of 1.99, meaning the equilibrium of the reaction SO42− (aq) +H+ (aq) = HSO4−(ag) will lie largely to the left as written.