C12.4 Separation and purification

Describe and explain methods of separation and purification using a suitable solvent

• Solvent must be chosen carefully depending on the type of solute that needs to be separated to ensure:

  • Only the desired substance should dissolve in the solvent

  • Other substances or impurities in the mixture should not dissolve in the solvent

Describe and explain methods of separation and purification using filtration

• Method used to separate insoluble solid, such as a precipitate, from a solution

  • A filter paper is placed in a filter funnel above another beaker, small pores only allow liquids to pass through

  • Mixture is poured into a beaker through a funnel, leaving insoluble solid behind as residue

Describe and explain methods of separation and purification using crystallisation

• Method used to separate dissolved solid from a solution

  • Heat solution in evaporating dish over bunsen burner until its boiling

  • Remove from heat and allow solution to cool and evaporate

  • Saturated solution will leave behind crystals as it cools

  • Crystals will grow and can be collected and allowed to dry

Describe and explain methods of separation and purification using simple distillation

• Simple distillation separates a solvent from a solution

  • Works because the dissolved solute has a much higher melting point than the solvent, so solvent boils first and evaporates

  • The solution is heated and solvent evaporates producing a vapour which rises through the neck of the round-bottomed flask

  • The vapour passes through the condenser, where it cools and condenses, turning into pure water which is collected in a beaker

  • After all the solvent is evaporated from the solution, only the solid solute will be left behind

Describe and explain methods of separation and purification using fractional distillation

• Fractional distillation separates a pure liquid from a mixture of liquids with different boiling points

  • The solution is heated to the temperature of the substance with the lowest boiling point

  • This substance will rise and evaporate first

  • The vapours will pass through a condenser, where they cool and condense

  • The condensed liquid is then collected in a beaker

  • All of the substance is evaporated and collected, leaving behind the other component(s) of the mixture

How can you assess purity with melting and boiling point information?

• Pure substances melt and boil at specific and sharp temperatures

• Mixtures have a range of melting and boiling points as they consist of different substances that melt or boil at different temperatures

  • Therefore, melting and boiling point data can be used to distinguish pure substances from mixtures