Saturated, Unsaturated and Supersaturated

Types of Solutions

• Saturated Solution

  • Contains the maximum amount of dissolved solute possible at a given temperature.

• Unsaturated Solution

  • Contains less dissolved solute than the maximum possible at that temperature.

• Supersaturated Solution

  • Contains more dissolved solute than what is typically possible at that temperature.
  • Formed by heating a saturated solution and then carefully cooling it down, allowing the solute to remain dissolved even at lower temperatures (unstable state).

Factors Affecting Solubility

• Temperature

  • Generally, solid solubility increases with temperature.
  • Example: Most ionic compounds become more soluble as temperature rises, except sodium sulfate, which becomes less soluble.
  • Notable exception: NaCl (table salt) shows little temperature dependence in solubility.
  • Gases: Become less soluble as temperature increases, meaning they are more soluble at lower temperatures.
  • Example: Carbon dioxide in soda retains its solubility at lower temperatures but escapes when the soda is warm, leading to carbonation loss (soda becoming flat).

• Amount of Solvent

  • More solvent means more solute can be dissolved.

• Nature of the Solute

  • Different solutes have different solubility characteristics; some dissolve easily, others do not.

Concentrated vs. Dilute Solutions

• Concentrated Solution

  • A solution that contains a large amount of dissolved solute.

• Dilute Solution

  • A solution with a small amount of dissolved solute.

• Key Insight:

  • A saturated or supersaturated solution can still be dilute if the amount of solute (in moles per liter) is low.
  • Example: Silver chloride (AgCl) has a saturated solution molarity of 1.33 \times 10^{-5}, which is very low, indicating it’s dilute despite being saturated.
  • In contrast, sodium chloride (NaCl) can have a concentrated solution that is not saturated (e.g., 2 ext{ M} vs. a saturated solution of 6 ext{ M}).

Demonstration of Supersaturation

• Supersaturated Solution of Sodium Acetate
  • Observed in a solution that holds more sodium acetate than typical at room temperature.
  • Supersaturated by heating and dissolving extra sodium acetate at a higher temperature before cooling.
  • When seed crystals are added, the excess solute crystallizes out rapidly, demonstrating the instability of the supersaturated state.

Conclusion

• Understanding the distinctions between saturated, unsaturated, and supersaturated solutions, along with factors affecting solubility, helps in comprehension of solution chemistry and behavior.