Solubility Equilibria Ksp. Solution A homogeneous mixture (solute + solvent) Solubility - a measure...

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Solubility Equilibria Ksp

Transcript of Solubility Equilibria Ksp. Solution A homogeneous mixture (solute + solvent) Solubility - a measure...

Page 1: Solubility Equilibria Ksp. Solution A homogeneous mixture (solute + solvent) Solubility - a measure of the maximum of solute that will dissolve in a given.

Solubility EquilibriaKsp

Page 2: Solubility Equilibria Ksp. Solution A homogeneous mixture (solute + solvent) Solubility - a measure of the maximum of solute that will dissolve in a given.

Solution• A homogeneous mixture (solute + solvent)

• Solubility - a measure of the maximum of solute that will dissolve in a given amount of solvent at a specified temperature (g/100ml or mol/L=molar solubility)

• Saturated Solution – contains maximum amount of dissolved solute possible at given temperature

• Supersaturated Solution – under unusual conditions a solvent will dissolve more than its maximum amount

Page 3: Solubility Equilibria Ksp. Solution A homogeneous mixture (solute + solvent) Solubility - a measure of the maximum of solute that will dissolve in a given.

Solubility Equilibrium

When salt dissolves in water to form a saturated solution, an equilibrium is created between the solid and its ions

Salts

Soluble Slightly Soluble

Insoluble

In Water

Page 4: Solubility Equilibria Ksp. Solution A homogeneous mixture (solute + solvent) Solubility - a measure of the maximum of solute that will dissolve in a given.

Dissolving a salt...

• A salt is an ionic compound - usually a metal cation bonded to a non-metal anion.

• The cations and anions are attracted to each other in the salt.

• They are also attracted to the water molecules.

• The water molecules will start to pull out some of the ions from the salt crystal.

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf

Page 5: Solubility Equilibria Ksp. Solution A homogeneous mixture (solute + solvent) Solubility - a measure of the maximum of solute that will dissolve in a given.

• At first, the only process occurring is the dissolving of the salt - the dissociation of the salt into its ions.

• However, soon the ions floating in the water begin to collide with the salt crystal and are “pulled back in” to the salt. (precipitation)

• Eventually the rate of dissociation is equal to the rate of precipitation.

• The solution is now “saturated”. It has reached equilibrium.

Page 6: Solubility Equilibria Ksp. Solution A homogeneous mixture (solute + solvent) Solubility - a measure of the maximum of solute that will dissolve in a given.

Solubility Equilibrium: Dissociation = Precipitation

In a saturated solution, there is no change in amount of solid precipitate at the bottom of the beaker.

Concentration of the solution is constant.

The rate at which the salt is dissolving into solution equals the rate of precipitation.Dissolving NaCl in water

Na+ and Cl - ions surrounded by water molecules

NaCl Crystal

Page 7: Solubility Equilibria Ksp. Solution A homogeneous mixture (solute + solvent) Solubility - a measure of the maximum of solute that will dissolve in a given.

Examples of Solubility of Salts and Solubility Equilibrium

• Kidney/bladder stones (Story Time)http://www2.canada.com/montrealgazette/news/insight/story.html?id=7c04b6f5-56c4-

479a-ade3-1491175551eb

• Barium sulfate

• Stalagmites and Stalactites

Page 8: Solubility Equilibria Ksp. Solution A homogeneous mixture (solute + solvent) Solubility - a measure of the maximum of solute that will dissolve in a given.

Barium Sulfate

Colon cancer

Page 9: Solubility Equilibria Ksp. Solution A homogeneous mixture (solute + solvent) Solubility - a measure of the maximum of solute that will dissolve in a given.

Stalagmites and Stalactites

Page 10: Solubility Equilibria Ksp. Solution A homogeneous mixture (solute + solvent) Solubility - a measure of the maximum of solute that will dissolve in a given.

Carbonate Ion EquilibriaReactions

(1) CO2(g) ↔ CO2(aq)

CO2(aq) + 2H2O(l) ↔ H3O+(l) + HCO3-(aq)

(2) CaCO3(s)+CO2(aq)+H2O(l)↔Ca2+(aq) + 2HCO3(aq)

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Ksp - Solubility Product Constant

• Measures how far to the right, the dissolution proceeds at equilibrium (saturated)

Ex. NaCl(s) Na+ (aq) + Cl- (aq)

Ksp = [Na+ (aq) ][Cl- (aq) ]

* Solids are not included• Since K is always calculated by just multiplying

concentrations, it is called a “solubility product” constant - Ksp.

Page 12: Solubility Equilibria Ksp. Solution A homogeneous mixture (solute + solvent) Solubility - a measure of the maximum of solute that will dissolve in a given.

Dissolving silver sulfate, Ag2SO4, in water

• When silver sulfate dissolves it dissociates into ions. When the solution is saturated, the following equilibrium exists:

Ag2SO4 (s) 2 Ag+ (aq) + SO42- (aq)

• Since this is an equilibrium, we can write an equilibrium expression for the reaction:

Ksp = [Ag+]2[SO42-]

Notice that the Ag2SO4 is left out of the expression! Why?

Since K is always calculated by just multiplying concentrations, it is called a “solubility product” constant - Ksp.

Page 13: Solubility Equilibria Ksp. Solution A homogeneous mixture (solute + solvent) Solubility - a measure of the maximum of solute that will dissolve in a given.

Writing solubility product expressions...

• For each salt below, write a balanced equation showing its dissociation in water.

• Then write the Ksp expression for the salt.

Iron (III) hydroxide, Fe(OH)3

Nickel sulfide, NiS

Silver chromate, Ag2CrO4

Zinc carbonate, ZnCO3

Calcium fluoride, CaF2

Page 14: Solubility Equilibria Ksp. Solution A homogeneous mixture (solute + solvent) Solubility - a measure of the maximum of solute that will dissolve in a given.

Some Ksp Values

Note: These are experimentally determined, and maybe slightly different on a different Ksp table.

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Determining Solubility (Equilibrium Concentrations) of Ions

Example: Calcium fluoride has a Ksp of 3.9x10-11 at 25°C. What is the solubility of the fluoride ion at equilibrium?

1) Write equation: CaF2(s) ↔ Ca2+(aq) + 2F-(aq)2) Write Ksp expression: Ksp = [Ca2+] [F-] 2 = 3.9x10-11

3) Create a RICE table to represent the equilibrium.

4) Ksp = (x)(2x)2 = 3.9x10-11

4x3 = 3.9x10-11

x3 = 9.8x10-12

x = 2.1x10-4 M for [Ca2+] and [F-] is 2x = 4.2x10-4 M

R CaF2(s) ↔ Ca2+ (aq) + 2F- (aq)

I 0 0

C +x +2x

E x 2x

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Determining the Ksp ConstantExample 2: The solubility of silver carbonate (Ag2CO3) is 3.6x10 -3 g/100 mL of solvent at 25˚C. Calculate the value of the solubility product constant of silver carbonate.

1) Convert g/100mL into units of molar solubility:

n = m = 3.6x10 -3 g x 1 mol = 1.3 x 10 -5 mol

MM 275.8 g

Molar Solubility = n = 1.3 x 10 -5 mol x 1000 mL = 1.3 x 10 -4 mol/L

v 100 mL 1 L

2) Find the concentration of each ion.

Ag2CO3 (s) ↔ 2 Ag+ (aq) + CO3 2- (aq)

3) Create a RICE table.

4) Ksp = [Ag +]2 [CO3 2-] = (2.6 x 10 -4 mol/L) 2 ∙ 1.3 x 10 -4 mol/L

= 8.8 x 10 -12

R Ag2CO3 (s) ↔ 2 Ag+ (aq) + CO3 2- (aq)

I 0 0

C +2.6 x 10 -4 mol/L +1.3 x 10 -4 mol/L

E 2.6 x 10 -4 mol/L 1.3 x 10 -4 mol/L

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The End