A laboratory technician prepares a saturated solution of lead(II) iodide, PbI₂, at 25 °C. After equilibrium is established, several crystals of potassium iodide, KI, are carefully added to the beaker, and the mixture is gently stirred until a new equilibrium is reached.
(a) Describe qualitatively how the concentration of Pb²⁺ ions in the solution changes after the KI crystals dissolve and a new equilibrium is attained.
(b) Explain the observed change in Pb²⁺ concentration in terms of the equilibrium that exists between solid PbI₂ and its ions in solution.
(c) Predict and justify whether the mass of solid PbI₂ present in the beaker increases, decreases, or remains the same after the KI is added and equilibrium is re-established.