Question

For each experiment described below 1) provide the relevant equilibrium reaction or reactions, 2) use LeChatelier's Principle to explain why the reaction has shifted left (L) or right (R), and 3) answer any other questions.

a) To a solution containing 1M Pb(NO3)2, 1 M HCl is slowly added until a white precipitate forms. The mixture is then heated and the precipitate disappears. Is the dissociation of the precipitate endothermic or exothermic? Does the equilibrium constant (Ksp) change when the solution is heated?

b) A few crystals of CoCl2 * 6H2O are dissolved with 2mL of 12 M HCl to form a blue solution. Water is slowly added until the mixture turns purple. More water is added and the solution turns pink. Why does the solution change color? Does the equilibrium constant (Ksp) for the reaction change with the addition of water?

c) A small amount of the slightly soluble solid Zn(OH)2 is prepared in water in three different test tubes. Some precipitate remains in each tube.

When 6M HCl is added to the first tube the precipitate disappears.

When 6M NaOH is added to the second tube the precipitate disappears

When 6M NH3 is added to the third tube the precipitate disappears.

Why did each addition cause the Zn)OH)2 to dissolve? Show reactions.

Don't forget for questions a-c to 1) provide the relevant equilibrium reaction or reactions, 2) use LeChatelier's Principle to explain why the reaction has shifted left (L) or right (R), and 3) answer any other questions.