Separation Techniques in Chemistry

Separation Techniques

  • Pure Substance:

    • Contains only one type of particle.
    • Example: Pure Na (s), Pure NaCl.

  • Impure Substance:

    • Contains more than one type of particle.
    • Can be a mixture of solids, solids + liquids, or liquids + liquids.

Separation Techniques

  1. Filtration:

    • Used to separate solids from liquids or solids from solids.
    • Involves the use of filter paper where the residue is retained, and the liquid that passes through is called the filtrate.
    • Example: Dissolving salt in water, then filtering to remove undissolved impurities.

  2. Evaporation:

    • The process of converting a liquid into vapor, allowing the solid solute to remain.
    • Heat the solution until dryness is achieved.
    • Example: Heating a salt solution to retrieve NaCl.

  3. Crystallisation:

    • Involves heating a solution until it reaches saturation point, then allowing it to cool.
    • Crystals of solute will form as it cools.
    • Example: The formation of blue crystals of hydrated copper (II) sulfate from a saturated solution.

Special Considerations

  • Exceptions:

    • For some solutions like sugar solutions, different techniques must be applied to retrieve the solute effectively.

  • Volatile Substances:

    • Substances that evaporate easily, which have lower molecular weights compared to non-volatile substances.

Distillation

  • Principle:

    • Based on the differences in boiling points of substances.
    • Used to extract solvents from solutions.
    • Example: Using distillation to separate salt and water from a salt solution.

  • Process:

    1. Heat the solution to evaporate the solvent.
    2. Vapors are then condensed back into liquid form in a separate flask.

Miscible vs Immiscible Liquids

  • Immiscible Liquids:

    • Liquids that do not mix (e.g., water and oil).

  • Miscible Liquids:

    • Liquids that mix completely (e.g., ethanol and water).

Fractional Distillation

  • Used for:
    • Separation of mixtures based on different boiling points, particularly useful for separating multiple liquids.
    • Example: The separation of alcohol from water in a mixture by heating until the desired component distills first.

Chromatography

  • Purpose:

    • A technique for separating and analyzing components of a mixture, mostly applicable for colored substances or those that can be visualized.
    • Involves a stationary phase and a mobile phase to separate components based on their movement on the medium.

  • Process:

    1. Apply a sample to a stationary phase (e.g., paper).
    2. The sample is then moved along the medium by the solvent.
    3. The distance traveled by the components can be measured as Rf (distance traveled by solute/distance traveled by solvent).

  • Locating agents can be used to visualize components that are colorless (e.g., using ninhydrin for amino acids).