UNIT III –SOLUBILITY EQUILIBRIUM

III.1Chem 11 Solubility Review

» Dissolves to give an electrically conducting solution containing ions

» e.g. ionic solutions

ELECTROLYTE

» Dissolves to give a non-conducting solution containing neutral molecules

» e.g. molecular solutions (especially organic compounds)

NON-ELECTROLYTE

Ionic solutionNa3PO4 (aq) ⇌ 3 Na+

(aq) + PO43-

(aq)

Molecular solutionCH3OH(g) ⇌ CH3OH (aq)

SOLUBILITY DEFINITION(CHEM 11 VERSION)

The maximum amount of substance which can dissolve in a given amount of solvent

at given temperature.

“saturated” solution

» Substance in lesser concentration, will be dissolved

SOLUTE

» Substance in greater concentration, dissolves the solute

SOLVENT

BETTER SOLUBILITY DEFINITION(CHEM 12 VERSION)

A substance’s solubility is itsequilibrium concentration in solution at a given temperature

“Molar solubility” when the concentration is expressed in

moles/litre or M

2 conditions required for saturation to exist: 1. Some undissolved mateirial

is present2. Equilibrium exists between

dissolved & undissolved material

Predict the equations for a compound such as K3PO4 in solution:

Equilibrium K3PO4 (s) ⇌ 3 K+(aq) + PO4

3-(aq)

Dissolving reaction K3PO4 (s) à 3 K+

(aq) + PO43-

(aq)

Crystallizationreaction 3 K+

(aq) + PO43-

(aq)à K3PO4 (s)

III.2Calculating Solubility & Ion Concentrations

Molar Solubility (M) = 𝒈𝒓𝒂𝒎𝒔𝒍𝒊𝒕𝒓𝒆

× 𝟏𝒎𝒐𝒍𝒎𝒐𝒍𝒂𝒓𝒎𝒂𝒔𝒔

ProblemThe molar solubility of Ag2CO3 is 1.2 x 10-4

M at 25°C. Give this value in grams/100 mL.

1.2×1023 4567× 89:.;<=456><8?@A

×0.100L

= 𝟑. 𝟑×𝟏𝟎2𝟑 𝐠

𝟏𝟎𝟎𝐦𝐋