Introduction to Solubility Equilibria

Understanding Solubility Equilibria

Solubility equilibrium refers to the state when a solute is dissolving and forming a solution at the same rate that it is re-forming into a solute.
This specific form of equilibrium occurs in saturated solutions, those in which no more solute can dissolve at a particular temperature.
Solubility is defined as the max amount of solute that can dissolve in a particular amount of solvent at a certain temperature.

Solubility Product Constant, Ksp

The solubility product constant (Ksp) is the equilibrium constant for a solid substance dissolving in an aqueous solution.
It denotes the level of solubility of a substance in a specific solvent at a particular temperature.
Importantly, each solid has a unique Ksp value.

Creating the Equilibrium Expression

The equilibrium expression involves setting up a product of the solubility of ions present in the solution, each to the power of its stoichiometric coefficient.
The solubility product constant expression does not contain any concentration terms of solid substances as their concentrations remain constant.

Solving for Solubility

The equation obtained from the Ksp expression can be solved for the unknown solubility.
When appropriate, approximation techniques or quadratic equation solutions may be required to solve for solubility.
Keep in mind the units of solubility typically include g/L, mole/L, or mole/litre.

Influence of Common Ions

The common ion effect occurs when a substance’s solubility decreases due to another substance adding a common ion to the solution.
This is due to Le Chatelier’s principle, which states that systems at equilibrium will respond to minimize changes. Therefore, when a common ion is added, the equilibrium shifts towards the solid to reduce the ion’s concentration.

Predicting Precipitation Reactions

A precipitation reaction happens when a change in conditions causes a product of a reaction to become insoluble and form a solid.
A key rule in prediction of precipitation is that if the ionic product of molar concentrations exceeds the Ksp, a precipitate will form.
Changing factors such as concentration, volume or adding another reagent can set off precipitation reactions.

Influence of pH and Temperature

The pH of the solution can significantly affect the solubility of substances, particularly of salts involving weak acidic or basic ions.
The effect of temperature on solubility varies: the solubility of gases decreases with increasing temperature, while the solubility of solids usually increases with increasing temperature.

Remember, revise smart and keep things balanced!