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Solubility Equilibrium

Lecture 11.5

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Solubility Equilibrium

Recall, solutions can be:

1) Unsaturated= contains less than the maximum amount of solute that will dissolve under a given set of conditions

3) Saturated= contains the maximum amount of solute that will dissolve under a given set of conditions

- at dynamic equilibrium with any undissolved solute

2) Supersaturated= contains more than the maximum amount of solute that will dissolve under a given set of conditions

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Solubility Equilibrium

- saturated solutions are

Consider the equation dissolution of BaSO4:

BaSO4 Ba+2 + SO4-2

Ksp = [Ba+2][SO4-2]

Ksp = solubility product constant

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Solubility Equilibrium

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Solubility Equilibrium

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Solubility Equilibrium

Ex: Copper (I) bromide has a measured molar solubility of 2.0 × 10−4

mol/L at 25°C. Calculate its Ksp value.

Ex: Calculate the Ksp value for bismuth sulfide (Bi2S3), which has a

molar solubility of 1.0 × 10−15 mol/L at 25°C.

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Solubility Equilibrium

Ex: The Ksp value for copper (II) iodate, Cu(IO3)2, is 1.4 × 10−7 at

25°C. Calculate its molar solubility at 25°C.

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Solubility Equilibrium

Ex: Calculate the molar solubility of Pb3(AsO4)2 from the solubility

product constant for Pb3(AsO4)2, Ksp = 4.1 x 10-36

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Common Ion Effect =

- another application of Le Chatalier’s Principle!

BaSO4 Ba+2 + SO4-2

Ex: BaSO4 in water

Ex: BaSO4 in water with Na2SO4 added

Na2SO4 is highly soluble so:

Na2SO4 2Na+1 + SO4-2

[SO4-2] is increased so:

BaSO4 Ba+2 + SO4-2

increased!

Equilibrium Shifts

- BaSO4 is now less soluble, and the Ksp decreases!!

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Common Ion Effect

Ex: Calculate the solubility of Ca(OH)2 in water (Ksp = 1.3 x 10-6).

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Common Ion Effect

Ex: Calculate the solubility of Ca(OH)2 in water in the presence of

0.10 M Ca(NO3)2 (Ksp of Ca(OH)2 = 1.3 x 10-6).

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Ksp , Q , and Predicting Formation of Precipitates

3 Situations:

1) Qsp < Ksp , not at equilibrium!

- more

3) Qsp > Ksp , not at equilibrium!

- more

2) Qsp = Ksp , equilibrium!

=

- saturated!

=

-

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Ksp , Q , and Predicting Formation of Precipitates

Ex: A solution is prepared by adding 750.0 mL of 4.00 × 10−3 M

Ce(NO3)3 to 300.0 mL of 2.00 × 10−2 M KIO3. Will Ce(IO3)3

(Ksp =1.9 × 10−10) precipitate from this solution? Justify your

answer.