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Purification and separation

What is a pure substance?

  • Single substance that is not mixed with anything else
  • Fixed melting and boiling point
  • Only produces a single spot on chromatogram

What is a mixture?

  • Consists of 2 or more substances that are mixed (not chemically combined together, can be separated)
  • An impure substance can be a mixture of more than 2 substances (water + sand + silt)
  • Melts and boils over a range of temperatures
  • Boiling point becomes higher
  • Melting point becomes lower

The importance of purity

  1. Extent of a reaction
  2. Efficiency of a reaction
  3. Efficacy of a chemical
  4. Price of a chemical

Separation technique

Easily separated using physical methods

Decanting

Separates an insoluble solid from a liquid by pouring off the liquid from the container carefully

Filtration

Used to separate an insoluble solid from a liquid

Apparatus:

  1. Beaker
  2. Filter funnel
  3. Filter paper

Key terms:

  • Residue
  • Filtrate

Evaporation to dryness

Separate dissolved solids from a solution

Some solids are not heat stable and will decompose when heated, even after evaporation, some impurities will still be present in the solution.

Apparatus:

  1. Evaporating dish

Crystallization

Separate dissolved solid from a solution, forming pure crystals of the substance

Filtrate has to be saturated before flame is turned off

Rinse crystals with cold distilled water (to remove impurities)

Solubility of solute decreases as temperature decreases, extra solute that cannot remain dissolved is separated as pure crystals

Apparatus:

  1. Evaporating dish
  2. Filter paper
  3. Bunsen burner
  4. Beaker
  5. Filter funnel
  6. Stirring rod

Key terms:

  • Filtrate
  • Solvent
  • Crystals
  • Impure solid

Sublimation

Used to separate a mixture of solids, one of which sublimes

Examples

  • Iodine in iodine and sand will sublime when heated
  • Solid CO2 (dry ice)

Ammonium compounds can also sublime

Simple distillation

Separates a pure liquid from a solution

Apparatus:

  1. Distillation flask
  2. Boiling chips
  3. Thermometer
  4. Liebig condenser
  5. Conical flask

Fractional distillation

Separate mixtures or miscible liquids with different boiling points

Chromatography

Used to separate and identify mixtures

Last update: June 11, 2023
Created: June 11, 2023