Consider a beaker containing a saturated solution of PbI2 in equilibrium with undissolved PbI2 (s).

(a) If solid KI is added to this solution, will the amount of solid PbI2 at the bottom of the beaker increase, decrease, or remain the same?

(b) Will the concentration of Pb^2 + ions in solution increase or decrease?

(c) Will the concentration of I - ions in solution increase or decrease?

(a) Increase the solid PbI₂ (s)

(b) Decrease

(c) Increase

Explanation:

In this question we are considering the effect of adding a common ion to an equilibrium.

The problem states that the saturated solution of PbI₂ is at equilibrium with undissolved PbI₂ (s):

PbI₂ (s) ⇄ Pb²⁺ + 2 I⁻

If we increase the concentration of I⁻ by adding the highly soluble KI, the equilibrium will react according to LeChatelier's principle by decreasing the concentration of Pb²⁺ precipitating some Pb²⁺ until it reaches equilibrium again. With this in mind, lets answer the question:

(a) Increase the solid PbI₂ (s)

(b) Decrease

(c) Increase