# Solubility Product

In the laboratory last week, you determined the concentration of chloride in our tap water using the Mohr titration.  The purpose of this activity is to understand in more detail the chemistry occurring in that titration.

Student Learning Outcomes

At the end of this exercise, students will be able to:

• Write the equilibrium expression and solubility product for a precipitation reaction.
• Calculate the solubility of a sparingly soluble compound.
• Predict the order of precipitation in a mixture.
• Predict the extent of precipitation in a mixture.

Complete the following.

1. Write the equilibrium expression for the chemical reaction

$\mathrm{AgCl(\mathit{s}) ⇌ Ag^+ + Cl^-}\nonumber$

1. Write the equilibrium expression for the chemical reaction

$\mathrm{Ag_2CrO _4(red,\mathit{s}) ⇌ 2Ag^+ + CrO_4^{2-}}\nonumber$

1. Calculate the solubility of AgCl. The Ksp for AgCl is 1.8 x 10-10. (answer = 13 µM)

1. Calculate the solubility of Ag2CrO4. The Ksp for Ag2CrO4 is 1.2 x 10-12. (answer = 67 µM)

1. The [Cl-] in our tap water is approximately 20 ppm. You added 4 drops of 0.5 M CrO42- to a 50 mL tap water sample.
1. Calculate the molarity of Cl- in the tap water sample. (answer = 5.6 x 10-4 M)

2. Calculate the molarity of CrO42- in the tap water sample. Assume that one drop has an approximate volume of 100 µL.  (answer = 4.0 x 10-3 M)

3. Is it possible to lower the concentration of Cl- by 99% by selective precipitation of Ag+ before precipitating CrO42-? Assume the Ag+ will react first with Cl-.  (answer = No,  4.1 x 10-12 > 1.2 x 10-12)

4. What percentage of Cl- will remain in solution when Ag2CrO4 begins to precipitate? (answer = 98%)