Soluble salts

• Soluble salts can be made from acids by reacting them with solid insoluable substances such as metals, metal oxides, hydroxides or carbonates.
• • During the preparation of soluble salts, the insoluble solid is added in excess to ensure that all of the acid has reacted
  • If this step is not completed, any unreacted acid would become dangerously concentrated during evaporation and crystallisation
• • The excess reactants (solid) then removed by filtration to ensure that only the salt and water remain
  • Since all of the acid has reacted and the excess solid base has been removed then the solution left can only be salt and water
  • The water is evaporated by heating until small crystals begin to appear
  • Allowing the filtered solution to evaporate slowly over a period of days results in the formation of larger crystals 
• 
  

  • A common example of making soluable salts is the preparation of copper(II) sulfate which can be made with copper(II) oxide and dilute sulfuric acid:

  
• • Acids can react with metal to produce the salt if:
  • The metal is above hydrogen in the reactivity series
  • The metal is not too reactive, which could result in a dangerous reaction
• Exam questions often ask why the solid oxide is added in excess. This is done to avoid leaving any unreacted acid which would become dangerously concentrated during evaporation and crystallisation.
• • If a carbonate was used as the solid base instead of an oxide or hydroxide, then any carbon dioxide gas produced would have been released into the atmosphere