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Define the common ion effect
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.
Define the solubility product constant (Ksp)
- 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.
What are the factors that affect solubility?
- 1. Temperature
- 2. Common Ion Effect
- 3. pH
- 4. Complex Ions
How does pH affect the solubility of a salt with an anion from a weak acid.
- The solubility of the salt increases as the concentration of the hydronium ion increases, i.e. the pH decreases.
- MnS(s) = Mn2+(aq) + S2-(aq)
- S2-(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.
Define the ion product (Q)
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.
How does Q relate to Ksp?
- Q > Ksp - Precipitation occurs
- Q = Ksp - Saturated solution
- Q < Ksp - No precipitate
Define selective precipitation
- Selective precipitation is a separation technique where ions are separated by succesive reactions with specific reagents.
Define complex ions
- 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.
Given the Ksp how is molar solubility calculated?
Using an ICE table
Given the molar solublity how is Ksp calculated?
By inserting the molar solubilities into the equilibrium calculation.
How is the concentration of the hydroxide ion calculated in buffered solutions?
The antilog of the negative pOH will show the molar concentration of the hydroxide ion.
Define the formation constant (Kf)
- 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)
Define the dissociation constant (Kd)
- The dissociation constant is the reciprocal of the formation constant.
- Kd = 1/Kf