 SOLUBILITY and PRECIPITATION

Topics & Terms

• Solubility
• Molarity
• Limiting Reactant
• Common-Ion Effect
• Solubility Product (Ksp)
• Precipitation

• Write the balanced ionic equation for the reaction. Determine initial concentrations moles per liter of reactants and products. (I = initial concentrations)
• Express the changes that will occur as the reaction proceeds. Subtract molarity concentration on the reactants side and add molarity concentration on the product side. (C = change concentrations)
• Express the equilibrium concentrations by combining the change and the initial concentrations. (E = equilibrium concentrations)
• Write the equilibrium expression, substitute concentrations and solve for the unknown.

Problem 2

What are the molar concentrations of ions in solution when solid PbI2 is in contact with pure water? (Ksp for PbI2 = 7.9 x 10-9)

(a) [Pb+2 ] = 1.3 x 10-3 M & [I-] = 2.6 x 10 -3 M
(b) [Pb+2] = 1.6 x 10-3 M & [I-] = 3.2 x 10-3 M
(c) [Pb+2] = [I-] = 2.0 x 10-3 M

Problem 5

Will CaSO4 precipitate if 50 mL of 0.0010 M CaCl2 is added to 50 mL of 0.010 M Na2SO4?
(Ksp for CaSO4 = 2.4 x 10-5)

(a) no precipitation will occur
(b) it is at equilibrium
(c) precipitation will occur