The Solubility Product Constant Ksp The Solubility Product
The Solubility Product Constant (Ksp)
The Solubility Product Constant • Remember not all salts are soluble! Ag. NO 3 (aq) + Na. Cl (aq) Ag. Cl (s) + Na. NO 3 (aq) • Write a net ionic equation for the above reaction: • Write Keq for the above equation
The Solubility Product Constant • Since some Ag. Cl remains an undissolved solid, the [Ag. Cl] is constant: Keq [Ag. Cl] = [Ag+]x[Cl-] = Ksp – Ksp = solubility product constant – Measured at 25ºC – Ksp for Ag. Cl = 1. 8 x 10 -10 • Equilibrium occurs only at and past saturation point…so only if there is a undissolved alt mixed with dissolved salt
Practice Problems • Write Ksp for each salt: – Pb. Cl 2 and Ag 2 Cr. O 4
Practice Problems • What is the Ag+ concentration in a saturated Ag. Cl solution at 25ºC? • ICE chart can be included but usually not necessary since initial concentration of the ions are considered 0. The salt dissolves and produces x amount of ions… 0 plus x equals x. (Ksp for Ag. Cl = 1. 8 x 10 -10)
Practice Problems • Calcium fluoride has a Ksp of 3. 9 x 10 -11 at 25ºC. What is the fluoride ion concentration at equilibrium?
The Common Ion Effect • Consider the following equation: Pb. Cr. O 4 Pb+2 + Cr. O 42 Ksp = 1. 8 x 10 -14 • What happens if we add lead (II) nitrate (Pb(NO 3)2)? – What are we really adding? – Think about Le Châtelier's Principle!
The Common Ion Effect Pb. Cr. O 4 Pb 2+ + Cr. O 42 - The Pb 2+ will precipitated until the product of Pb 2+ and Cr. O 42 - is 1. 8 x 10 -14 Extra Pb 2+ Added The Ksp (just like the Keq) does not change when you add a reactant or product, the reaction shifts to accommodate this addition.
The Common Ion Effect • Common Ion: an ion added that is common to both salts – Pb 2+ was common to Pb. Cr. O 4 and Pb(NO 3)2 • Adding a common ion causes solubility to decrease – Called the common ion effect
Common Ion Problems • The Ksp of Ag. I is 8. 3 x 10 -17. What is the iodideion concentration of a 1. 00 -L saturated solution of Ag. I to which 0. 020 mol Ag. NO 3 is added? • With a common ion, an ICE chart could be useful.
Another problem… • Would precipitation occur when 500 m. L of a 0. 02 M solution of Ag. NO 3 is mixed with 500 m. L of a 0. 001 M solution of Na. Cl? (K for Ag. Cl = 1. 8 x 10 -10) sp
Before you go… • A student prepares a solution by combining 0. 025 mol calcium chloride and 0. 015 mol lead (II) nitrate and adding water to make 1. 0 L of solution. Will a precipitate of lead (II) chloride form in this solution. • Ksp = 1. 7 x 10 -5
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