Types of Solutions and Determination of Solubility

Sarp Series

Types of Solutions

  • Unsaturated Solution

    • An unsaturated solution is defined as one that can dissolve more solute at a given temperature.

  • Saturated Solution

    • A saturated solution is one that cannot dissolve any more solute at a given temperature, even when undissolved solute is present.
    • Alternative Definition: A saturated solution is also described as a solution in which the undissolved solute is in dynamic equilibrium with its dissolved ions or molecules at a specific temperature.
    • Example: The dissolution equilibrium can be represented as follows:
    • 2Na{(aq)} + SO4^{2-}_{(aq)}
    • For example, in the case of sodium sulfate (Na2SO4) in aqueous solution:
      • ext{At Equilibrium, Rate of dissolution} = ext{Rate of crystallization}
    • In a saturated solution, the concentrations of both the undissolved solute and its ions/molecules remain constant at a given temperature. Any added solute will dissolve at the same rate as the ions/molecules that crystallize out.
    • When a saturated solution is heated, the solute will fully dissolve, and upon cooling, the solute will form crystals upon deposition.

  • Supersaturated Solution

    • A supersaturated solution contains more solute than what can be dissolved at a given temperature, even in the presence of undissolved solute.
    • Characteristics: Supersaturated solutions are more than saturated and are typically in an unstable condition.
    • Examples of compounds: Some compounds that can form supersaturated solutions include Glauber's salt (Na2SO4 ullet 10H2O) and sodium thiosulfate (Na2S2O3 ullet 5H_2O).
    • Preparation Method:
    • To create a supersaturated solution, one must:
      • Cool a hot saturated solution slowly.
      • Keep crystals, dust, and other small particles away, as they may act as nucleation sites for crystallization.
      • Avoid shaking or disturbing the solution.

Determination of Solubility

  • The term solubility refers to the extent to which a solid solute can dissolve in a solvent.
  • Definition: Solubility is defined as the maximum quantity of solute (in moles or grams) that can saturate 1 dm³ of solvent at a specific temperature.
    • Alternative Definition: It represents the maximum quantity of solute that can dissolve in 1 dm³ of solvent to form a saturated solution at a given temperature.
    • Solubility is typically measured in moles per dm³.

Factors that Affect Solubility

  1. Nature of the Solute

    • The inherent characteristics of the solute can influence how well it dissolves in solvent.

  2. Nature of the Solvent

    • The compatibility of the solvent in relation to the solute plays a critical role in solubility.

  3. Temperature

    • Generally, solubility increases with temperature for most solid solutes and typically decreases for gases.

  4. Pressure (for Gases Only)

    • The solubility of gases is significantly affected by pressure; an increase in pressure increases the solubility of a gas in a liquid.