Chapter 21 Notes, part III Ksp and Common Ion Effect.

Chapter 21 Notes, part IIIKsp and Common Ion EffectKsp and Common Ion Effect

Solubility Product Constant• Salts have different solubilities; even Salts have different solubilities; even

salts we earlier considered insoluble salts we earlier considered insoluble have a very, very small amount of have a very, very small amount of solubility in water.solubility in water.

• The solubility product constant (KThe solubility product constant (Kspsp) )

is an index of how soluble a salt is—is an index of how soluble a salt is—the bigger the Ksp, the more soluble the bigger the Ksp, the more soluble the salt is.the salt is.

Ksp

• KKspsp is based on K is based on Keqeq from Ch. 19; for from Ch. 19; for

example:example:

• KKeqeq for AgCl(s) for AgCl(s) Ag Ag++(aq) + Cl(aq) + Cl--(aq) (aq)

would be:would be:

KKeqeq = =

• But a solid is not dissolved, and thus But a solid is not dissolved, and thus does not have a constant, so:does not have a constant, so:

KKspsp = [Ag = [Ag++][Cl][Cl--]]

[Ag[Ag++][Cl][Cl--] ] [AgCl][AgCl]

Practice Problem #1• What is the Ksp for AgWhat is the Ksp for Ag22SOSO44 if its if its

solubility is 3.5x10solubility is 3.5x10-10-10M?M?

Practice Problem #2• What is the concentration of silver What is the concentration of silver

ions and chlorine ions in AgCl if ions and chlorine ions in AgCl if KKspsp=1.8x10=1.8x10-10-10 at 25 at 25ooC?C?

Practice Problem #3• Calcium fluoride has KCalcium fluoride has Kspsp=3.9x10=3.9x10-11-11. .

What is the concentration of fluoride What is the concentration of fluoride ions?ions?

Practice Problem #4• KKspsp for Ag for Ag22S is 8x10S is 8x10-51-51. What is the . What is the

concentration of Agconcentration of Ag++ ions? ions?

Common Ion Effect• A A common ioncommon ion is an ion that two salts is an ion that two salts

or a salt and an acid or base have in or a salt and an acid or base have in common.common.

• The lowering of solubility of a The lowering of solubility of a substance by the addition of a substance by the addition of a common ion is called the common ion is called the common common ion effection effect..

Common Ion Effect• For example:For example:

• PbCrOPbCrO44 Pb Pb2+2+ + CrO + CrO442-2- Ksp=1.8x10 Ksp=1.8x10-14-14

• If we add lead (II) nitrate (Pb(NOIf we add lead (II) nitrate (Pb(NO33))22), ),

we are adding a common ion (see the we are adding a common ion (see the dissociation reaction on the board).dissociation reaction on the board).

Common Ion Effect• Due to LeChatelier’s principle, the Due to LeChatelier’s principle, the

reaction will shift left because of the reaction will shift left because of the increased Pbincreased Pb2+2+ concentration, concentration, causing formation of PbCrOcausing formation of PbCrO44 solid. solid.

Practice Problem #5• Predict whether barium sulfate will Predict whether barium sulfate will

precipitate if of 0.0010mol barium precipitate if of 0.0010mol barium nitrate is mixed with 1.0L of 0.0040M nitrate is mixed with 1.0L of 0.0040M sodium sulfate to form a 1.0L sodium sulfate to form a 1.0L solution (Ksp of BaSOsolution (Ksp of BaSO44 = 1.1x10 = 1.1x10-10-10))

Practice Problem #6• Predict whether silver cyanide will Predict whether silver cyanide will

precipitate if 500mL of 0.00012M precipitate if 500mL of 0.00012M silver nitrate is mixed with 500mL of silver nitrate is mixed with 500mL of 0.00040M sodium cyanide to form a 0.00040M sodium cyanide to form a 1.0L solution (Ksp of AgCN=2.0x101.0L solution (Ksp of AgCN=2.0x10-12-12))