Chemical Solubility

When a salt is added to a solution that has either the anion or the cation of that salt already present the common ion effect occurs. The effect alters the equilibrium that forms between the salt and the solution according to LeChatelier's principle.

• The product of the concentration of the ions present (raised to the power of their balancing coefficients). The concentrations are those when an aqueous solution is saturated.
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• 1. Temperature
• 2. Common Ion Effect
• 3. pH
• 4. Complex Ions

• The solubility of the salt increases as the concentration of the hydronium ion increases, i.e. the pH decreases.
• MnS_(s) = Mn²⁺_(aq) + S^2-_(aq)
• S^2-_(aq) + 2H⁺_(aq) = H₂S_(aq)
• MnS_(s) + 2H⁺_(aq) = Mn²⁺_(aq) + H₂S_(aq)

Certain metals, e.g. aluminium, chromium, zinc, and tin, form amphoteric oxides and hydroxides. These salts are mostly insoluble in neutral solutions but become highly soluble in acidic or basic solutions.

The ion product can be calculated by multiplying the initial concentrations of the ions of an anion and cation that may form an insoluble precipitate.

• Q > Ksp - Precipitation occurs
• Q = Ksp - Saturated solution
• Q < Ksp - No precipitate

• Selective precipitation is a separation technique where ions are separated by succesive reactions with specific reagents.
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• Complex ions form as the result of a reaction between a Lewis base, other than water, and metal ions. The solubility of the metal salts increases in the presence of a suitable Lewis bases (e.g. ammonia, cyano, or hydroxide) if the metal forms a complex with the base.
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Using an ICE table

By inserting the molar solubilities into the equilibrium calculation.

The antilog of the negative pOH will show the molar concentration of the hydroxide ion.

• The formation constant is equilibrium constant for the formation of a complex ion.
• Kf = (concentration of the complex ion)/(the concentrations of the component ions)

• The dissociation constant is the reciprocal of the formation constant.
• Kd = 1/Kf