Making soluble salts

• Salt


  A compound containing a positive ion (metal ion) and a negative ion (from an acid)
• Sources of metal ions for salts

  • Metal
  • Metal oxide
  • Metal hydroxide
  • Metal carbonate
• Negative ion in a salt

  Comes from the acid
• Making a soluble salt using an acid


  1. Use dilute acid as limiting reactant

  2. Heat acid almost to boiling

  3. Add small amounts of metal oxide and stir

  4. Stop adding oxide when solution is blue

  5. Filter out unreacted oxide

  6. Evaporate solution to form crystals

  7. Allow crystals to form over 24 hours

  8. Dry the crystals
• Example salt


  • Copper sulfate
• Copper sulfate


  • Contains copper(II) ion as positive ion
  • Contains sulfate ion as negative ion
• Cannot make copper sulfate by reacting copper metal with dilute sulfuric acid
• Copper is not reactive enough for that reaction to take place
• Need to use copper oxide or copper carbonate to make copper sulfate
• Reaction must use up all the acid to avoid contamination
• Filtering removes unreacted copper oxide
• Evaporation and crystallisation forms pure copper sulfate crystals