Lecture 18.3- Solubility

Bellwork- Le ChatThe system described by the equation 2H2(g) + O2(g) 2H2O(g) ΔH= -241.8kJ

is at equilibrium.

a)How does the concentration of H2 gaschange?b)Do H2 molecules react?c)What happens to the H2 concentration if the

container’s volume is reduced?d)What happens to the H2 concentration if temperature is increased?

SolubilityThe final concentration of ions insolution is different for every substance.Insoluble very few ions in solution

The solubility product constant (Ksp), equals theproduct of the concentrations of the ions, each raisedto a power equal to the coefficient of the ion in thedissociation equation.

Example-

PbCl2(s) Pb2+(aq) + 2Cl-(aq)

Ksp= [Pb2+][Cl-]2= 1.7x10-5

The smaller the solubilityproduct constant (Ksp), the lowerthe solubility of the compound.

18.3

18.3

Silver chloride is slightly soluble in water.

18.3

Scale, formed by the precipitation of slightlysoluble salts, builds up around faucets.

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18.3

for Sample Problem 18.3

If the product of theconcentrations is greater thanthe Ksp, a precipitate will form.

18.3PbCl2(s) Pb2+(aq) + 2Cl-(aq)

Ksp= [Pb2+][Cl-]2= 1.7x10-5

The Common Ion Effect

A common ion is an ion that is foundin both salts in a solution.

Common ion effect- solubility lowerswhen a common ion is added

18.3

The Common Ion Effect

A saturatedsolution oflead(II)chromate ispale yellow.

When a few dropsof lead nitrate areadded to thesolution, morelead(II) chromateprecipitates.

The Common Ion Effect

Ksp = [Pb2+][CrO42+]

Aconstant

Whenthis

goesup↑

Thismust

godown↓

Precipitationoccurs untilKsp is againsatisfied

18.3

Le Chatelier’s PrinciplePbCrO4(s) Pb2+(aq) + CrO4

2+(aq)IncreasePb2+Shift left to

remove Pb2+

Moresolid isformed

The Common Ion Effect

1. What is the concentration of a saturatedsolution of silver sulfide?

The Ksp of Ag2S is 8.0 × 10-51.

a. 2.0 × 10-17M

b. 8.9 × 10-26M

c. 8.9 × 10-25M

d. 2.0 × 1017M

18.3 Section Quiz.

2. Adding which of these solutions to a saturatedsolution of BaSO4 will cause the solubility ofBaSO4 to decrease?

I. BaCl2(aq)II. Na2SO4 (aq)

a. (I) only

b. (II) only

c. (I) and (II)

d. neither solution

18.3 Section Quiz.

3. The Ksp of AgBr is 5.0 × 10-13. When 7.1 × 10-6

mol/L solutions of NaBr(aq) and AgNO3(aq)are mixed, we would expect

a. no precipitate to form.

b. a definite precipitation reaction.

c. no reaction.

d. a saturated solution but no visibleprecipitation.

18.3 Section Quiz.

4. After the common ion effect causes aprecipitate to form in a solution,

a. the solution will no longer be saturated.

b. the solution will again be saturated.

c. the solution will be supersaturated.

d. there will be no solute left in the solution.

18.3 Section Quiz.