1.7.7

Introduction to Solubility Equilibria

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Introduction to Solubility Equilibria

Solubility equilibria are established when the dissolution and precipitation of a solute species occur at equal rates.

Solubility product

Solubility product

  • The solubility of a substance can vary from essentially zero (insoluble or sparingly soluble) to infinity (miscible).
  • A solute with finite solubility can yield a saturated solution when it is added to a solvent in an amount exceeding its solubility.
    • This results in a heterogeneous mixture of the saturated solution and the excess, undissolved solute.
Example

Example

  • For example, a saturated solution of silver chloride is one in which the equilibrium shown above has been established.
  • In this solution, an excess of solid AgCl dissolves and dissociates to produce aqueous Ag+ and Cl ions at the same rate that these aqueous ions combine and precipitate to form solid AgCl.
    • Because silver chloride is a sparingly soluble salt, the equilibrium concentration of its dissolved ions in the solution is relatively low.
𝐾<sub>sp</sub>

𝐾sp

  • The equilibrium constant for solubility equilibria such as this one is called the solubility product constant, 𝐾sp, in this case:
    • AgCl(s)⇌Ag+(aq)+Cl(aq)
    • 𝐾sp=[Ag+(aq)][Cl(aq)]
  • Recall that only gasses and solutes are represented in equilibrium constant expressions, so the 𝐾sp does not include a term for the undissolved AgCl.
Interpreting 𝐾<sub>sp</sub>

Interpreting 𝐾sp

  • A 𝐾sp value of greater than one means a salt is soluble.
    • Calculating 𝐾sp is covered in the next section.
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Physical Chemistry

1.1

Atoms, Molecules & Stoichiometry

1.2

Atomic Structure

1.3

Chemical Bonding

1.4

States of Matter

1.5

Chemical Energetics

1.6

Electrochemistry

1.7

Equilibria

1.8

Partition Coefficient

1.9

Reaction Kinetics

2

Inorganic Chemistry

3

Organic Chemistry & Analysis

3.1

Introduction to Organic Chemistry

3.2

Hydrocarbons

3.3

Halogen Derivatives

3.4

Hydroxy Compounds

3.5

Carbonyl Compounds

3.6

Carboxylic Acids & Derivatives

3.7

Nitrogen Compounds

3.8

Polymerisation

3.9

Analytical Techniques

3.10

Organic Synthesis

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