If a salt forms a basic anion, then adding acid (lowering the pH) will _______________ solubility.

If a salt forms a basic anion, then adding acid (lowering the pH) will _______________ solubility.

• A. Decrease
• B. No effect
• C. Stay the same
• D. Increase

Answer: (D)

A salt that has a basic (conjugate base) anion tends to hydrolyze in water: the anion reacts with water to form its weak acid and OH−. This hydrolysis pulls the dissolved anion out of solution, so more solid salt dissolves to replace it, increasing solubility. When you add acid, the basic anion is protonated: A− + H+ → HA. This removes the A− from the solution and suppresses its hydrolysis. To maintain the dissolution equilibrium MX(s) ⇌ M+ + X−, more MX needs to dissolve to supply fresh X−. Thus the overall solubility increases in acidic conditions.

A salt that has a basic (conjugate base) anion tends to hydrolyze in water: the anion reacts with water to form its weak acid and OH−. This hydrolysis pulls the dissolved anion out of solution, so more solid salt dissolves to replace it, increasing solubility.

When you add acid, the basic anion is protonated: A− + H+ → HA. This removes the A− from the solution and suppresses its hydrolysis. To maintain the dissolution equilibrium MX(s) ⇌ M+ + X−, more MX needs to dissolve to supply fresh X−. Thus the overall solubility increases in acidic conditions.