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

the law of conservation of mass states that in a chemical reaction, the total mass of reactants is equal to the total mass of products. because atoms are only rearranged in a chemical reaction, there must be the same number of sodium atoms and chlorine atoms in both the reactants and products