Solubility of the Common Salts

Specification Point 3.19:
  • Recall the general rules which describe the solubility of common types of substances in water:
    a) all common sodium, potassium and ammonium salts are soluble
    b) all nitrates are soluble
    c) common chlorides are soluble except those of silver and lead
    d) common sulfates are soluble except those of lead, barium and calcium
    e) common carbonates and hydroxides are insoluble except those of sodium, potassium and ammonium
  • Solubility is a measure of the maximum mass of a solid substance(solute) that can dissolve in a given volume of liquid (solvent).
  • Solubility is temperature dependent, substances dissolve more at higher temperatures.
  • Substances that are soluble have high solubility.
  • Substances that are insoluble or sparingly soluble have very low solubility.
  • The table below indicates the solubility of the more common salts and is used in determining appropriate methods of preparation.

Solubility of common salts table, Edexcel GCSE Chemistry

Predicting Solubility

Specification Point 3.20:
  • Predict, using solubility rules, whether or not a precipitate will be formed when named solutions are mixed together, naming the precipitate if any
  • Some salts can be extracted by mining but others need to be prepared in the laboratory.
  • How the salt is made in the laboratory depends on whether the salt being formed is soluble or insoluble in water.
  • To do this the balanced equation is written down to determine the identify of the salt product.
  • Then check the solubility of the salt using the solubility table.
  • If it is soluble in water, then it can be prepared by titration.
  • If it is insoluble then it can be prepared by precipitation.
  • For example a silver nitrate solution is mixed with a sodium chloride solution:

AgNO3 + NaCl → AgCl + NaNO3

  • From the table both AgNO3 and NaCl are water soluble but AgCl is not and hence forms a  precipitate.

Preparing an Insoluble Salt

Specification Point 3.21:
  • Describe the method used to prepare a pure, dry sample of an insoluble salt

Preparing an Insoluble Salt

Aim: 

To prepare a pure, dry sample of an insoluble salt

Salt Filtration Step, Edexcel GCSE Chemistry

Diagram showing the filtration step to separate the insoluble salt from solution

Materials:

  • Dilute acid, insoluble metal base or carbonate, goggles and lab coat
  • Beakers, funnel and filter paper, wash bottle, oven, glass rod

Method:

  • Dissolve the soluble salts in water and mix together using a stirring rod in a beaker.
  • Filter to remove precipitate from mixture. 
  • Wash filtrate with deionised water to remove traces of other solutions.
  • Leave in an oven to dry.

Analysis of results:

  • This is a relatively quick and simple way of producing an insoluble salt.
  • After drying comment on the shape and appearance of the salt crystals.

Conclusion:

  • Since the precipitate is insoluble in water any remaining contaminating solution can be removed by washing it with deionised water.

Edexcel GCSE Chemistry Notes

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.