SOLUBILITY and PRECIPITATION

Topics & Terms

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

Helpful Hints....

• 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 1

The value of Ksp of AgCl is 1.8 x 10^-10. What would be the molar concentration of Ag⁺ and Cl^- in AgCl in pure water placed in contact with solid AgCl(s)?

(a) 1.8 x 10 ^-10 M
(b) 1.3 x 10 ^-5 M
(c) 3.24 x 10 ^-20 M

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 3

What is the molar concentration of [Ag⁺] in AgCl solution in 0.10 M NaCl ?
(Ksp = 1.8 x 10^-10) Remember that in this case the molar solubility of AgCl is equal to the [Ag⁺] as only the Ag⁺ reflects the amount of AgCl that dissolved.

(a) Ag+ = 1.3 x 10^-5 M
(b) Ag+ = 0.10 M
(c) Ag+ = [AgCl] = 1.8 x 10^-9 M

Problem 4

The molar solubility of PbCl₂ in 0.10 M NaCl is 1.7 x 10^-3 moles in a liter (that is 1.7 x 10^-3 moles of PbCl₂ will dissolve in 1 liter of the solution). What is the Ksp of PbCl₂?

(a) Ksp = 1.8 x 10^-5
(b) Ksp = 1.9 x 10^-8
(c) Ksp = 1.7 x 10^-4

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

Problem 6

How many grams (g) of CaSO₄ is formed when 20 mL of 0.010 M Na₂SO₄ is added to 100 mL of 0.001 M CaCl₂?

(a) 0.0001g
(b) 0.01g
(c) 0.0002g