C8.3 – Preparation of Salts

1. Describe the preparation, separation and purification of salts using techniques selected from section C2.1 and the reactions specified in section C8.1.

Salts can be prepared by simply mixing together elements and compounds. For an aqueous solution, add water.

(Refer to this topic for more details on separation and purifying techniques).

Distillation separates the liquid and salt from a solution.
Salty water is heated so that the water evaporates and condenses back into water in the condenser, leaving behind the salt in the flask.

Filtration: is used to separate an insoluble solid from a liquid. A beaker containing a mixture of solid and liquid is poured into a flask through a filter funnel (plastered in filter paper).The liquid drips through the filter paper into the flask but the solid particles are caught in the filter paper.

Crystallization: when a product is made of a solution, one way to separate it from a solution is to make crystals. This involves evaporating the solution to a much smaller volume and then leaving it to cool. As the solution cools, crystals form and these can be obtained by filtration.

2. Suggest a method of making a given salt from suitable starting materials, given
   appropriate information.

• Acid + alkali –> salt + water
  Example: Hydrochloric acid + sodium hydroxide –> sodium chloride (salt) + water
  • Add sodium hydroxide to a flask
  • Add the hydrochloric acid to the flask
  • The solution will turn colourless when neutralised
  • Heat the solution to evaporate the liquid and obtain the salt

• Acid + metal –> salt + hydrogen
  Example: Sulphuric acid + zinc –> zinc sulphate (salt) + hydrogen
  • Add zinc to a flask of the acid
  • When the zinc dissolves, hydrogen bubbles will appear
  • Filter the solution to remove the excess zinc
  • Heat the solution to evaporate the liquid and obtain the salt

• Acid + base –> salt + water
  Example: Sulphuric acid + iron(II) oxide –> iron sulphate (salt) + water
  • Add and excess of iron oxide to the sulphuric acid
  • Filter the solution to remove the excess iron oxide
  • Heat the solution to evaporate the liquid and obtain the salt

Note: Whenever there is excess substance, filter it off.

Notes submitted by Lintha

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