Unit 1.10 Separating Mixtures: Distillation

Distillation purpose: used to separate mixtures, especially to separate a liquid and a soluble solid from a solution (e.g., water and salt from saline solution).
Distillation types:
- Simple distillation
- Fractional distillation
Distillation is effective when components have sufficiently different boiling points; not ideal when boiling points are similar.
Apparatus concept (from diagrams): heating, vapor formation, condensation via a cooling jacket, and collection of the distillate; the remaining solution stays in the original flask.
The process can yield pure water from a saline solution via simple distillation (as illustrated by the water vapor, saline solution, and condensation setup).

Steps:
1. The solution is heated.
- The component with the lowest boiling point evaporates first.
1. The vapor is cooled and condensed.
- Condensation is aided by a cooling water jacket.
1. The newly condensed, pure liquid is collected in a new container.
2. The remainder of the solution stays in the original flask.
Practical note: Simple distillation is suitable when the mixture contains components with very different boiling points.
Example in diagrams: Obtaining pure water from saline solution using simple distillation (water is heated to boiling, vapor condenses in the water jacket, droplets form and collect as pure water).

Purpose: used to separate mixtures of liquids when boiling points are closer to each other.
Common example: separation of ethanol and water.
- Ethanol formula: ext{EtOH} = \,\mathrm{C2H5OH}
- Water formula: \mathrm{H_2O}
- Boiling points: ethanol T{\mathrm{EtOH}} = 78^\circ\mathrm{C}, water T{\mathrm{H_2O}} = 100^\circ\mathrm{C}
Process:
- The liquid with the lowest boiling point evaporates first (ethanol in this example).
- The ethanol vapour rises up the fractionating column.
- The vapour is carried to a condenser where it condenses back into a liquid.
- The temperature is then raised so that the second liquid (water) can be collected.
Apparatus details:
- Fractionating column provides repeated condensation and vaporization to improve separation.
- Water jacket and electric heater are used to heat and cool the system; a condenser returns condensed liquid to the collection vessel.
Outcome: Pure, distilled ethanol can be collected after the process.

Boiling point differences drive separation: the component with the lower boiling point vaporizes first and can be separated from the mixture.
Phase change fundamentals: heating causes boiling; the vapor must be cooled to condense into a liquid that can be collected.
Fractionating column increases surface area for repeated evaporation-condensation cycles, improving separation for close-boiling components.
Distillation assumes the target distillate is more volatile (lower boiling point) than the remainder.
Practical implications:
- Simple distillation is fast and simple but limited to large boiling-point differences.
- Fractional distillation handles closer boiling points but is more complex and slower.
- Distillation can produce relatively pure liquids (e.g., pure water or ethanol) but may require multiple stages or additional purification for very high purity.

Filtration
Crystallisation
Paper chromatography
These techniques serve different separation goals (particle-sized solids, crystallization of a solute, or separation of components by chromatography) and are part of the broader topic of separating mixtures.

Boiling points in the ethanol-water example:
- Ethanol: T_{\mathrm{EtOH}} = 78^\circ\mathrm{C}
- Water: T{\mathrm{H2O}} = 100^\circ\mathrm{C}
Ethanol chemical representation: \mathrm{C2H5OH}

Distillation is widely used in laboratories and industries to purify liquids, make solvents, and separate components in crude mixtures.
The choice between simple and fractional distillation depends on the boiling-point gap between components and the required purity of the distillate.