Describe and explain methods of separation and purification using: (a) a suitable solvent (b) filtration (c) crystallisation (d) simple distillation (e) fractional distillation

(a) Separation using a Suitable Solvent

Think of a solvent as a friendly helper that can dissolve some substances but not others. When you mix a mixture with the right solvent, the component that dissolves forms a solution, while the rest stays solid or floats on top.

1. Choose a solvent that dissolves the target compound but not the impurities.
2. Heat gently if needed to increase solubility.
3. Filter or decant to remove undissolved solids.
4. Evaporate the solvent to recover the purified compound.

🔬 Analogy: Imagine a sponge (solvent) soaking up only the blue dye (target) from a mixture of blue and red dyes.

(b) Filtration

Filtration separates solids from liquids using a porous barrier.

• Use a filter paper or a membrane.
• Place the filter in a funnel and pour the mixture.
• Collect the filtrate (liquid) below; the residue stays on the filter.

🧹 Analogy: Think of a coffee filter that lets liquid coffee through but keeps the grounds out.

(c) Crystallisation

Crystallisation purifies by forming a solid lattice from a saturated solution.

1. Dissolve the impure solid in a hot solvent.
2. Cool slowly to allow crystals to grow.
3. Filter the crystals from the mother liquor.
4. Wash with cold solvent to remove surface impurities.

⚗️ Analogy: Like making ice cubes: water (solvent) freezes into pure ice (crystals) while impurities stay in the liquid.

(d) Simple Distillation

Used when two liquids have a large difference in boiling points.

1. Heat the mixture in a flask.
2. Boiling vapour rises and condenses in a cooler section.
3. Collect the condensate (distillate) in a receiver.

🌊 Analogy: Think of boiling tea: the steam (vapour) carries the flavour (volatile component) which condenses back as liquid.

(e) Fractional Distillation

Used when boiling points are close; a fractionating column provides many theoretical plates for better separation.

1. Heat the mixture in a flask.
2. Vapour rises through the column, condensing and re‑boiling repeatedly.
3. Collect fractions at different temperatures.

🔬 Analogy: Like a multi‑stage water filter that removes finer particles at each stage.