Salt preperations

• Acids


  React with metals, bases and carbonates to form salts
• Preparation of salt crystals from acids

  • Depends on whether the substances they are reacting with are soluble or insoluble
• Preparation of a salt from a metal or insoluble base/carbonate

  1. Excess metal/base/carbonate is added to the acid to make sure all the acid has reacted and been used up

  2. Heating and stirring help the process

  3. For metals and metal carbonates, the fizzing stops when all the acid has been used up

  4. The mixture is filtered using a filter funnel and filter paper

  5. The excess solid remains in the filter paper. The salt solution passes through into the evaporating basin

  6. The salt crystals are collected from the solution by evaporation
• Large crystals


  Evaporate water slowly near a radiator or window ledge
• Small crystals


  Use a Bunsen to evaporate 2/3 of the water quickly, before allowing to crystallise naturally
• Alkali


  A soluble base
• Preparation of a salt from an alkali or soluble carbonate

  1. Measure exactly 25 cm3 of alkali into a clean conical flask

  2. Add a few drops of indicator to the flask

  3. Place the flask onto a white tile

  4. Fill the burette with acid

  5. Slowly add the acid from the burette to the alkali until the indicator changes colour. This is the endpoint of the reaction

  6. Record the volume of acid added to the flask

  7. Repeat steps 1-6 without using the indicator and adding the same volume of acid from the burette
• The salt crystals are collected from the solution by evaporation
• The same method works for adding an alkali to an acid - just swap around the solutions that go into the flask and burette
• Preparing Insoluble Salts


  1. Mixing - The two soluble salt solutions are mixed

  2. Filtration - The insoluble precipitate is separated from the mixture by filtration. The precipitate stays behind in the filter paper, while the solution passes through

  3. Washing and drying - Water cannot dissolve the precipitate - it is insoluble - but it can wash off any remaining impurities. The filter paper is then removed, opened out and the precipitate dried in an oven
• Concentration


  The number of moles per dm3
• Titration Calculation


  1. Convert all volumes to dm3

  2. Calculate the number of moles of the substance where the volume and concentration are known

  3. Calculate the unknown concentration
• 1. 1 Mole Ratio


  • 15.0 cm3 of 0.1 mol/dm3 hydrochloric acid was needed to neutralise 25.0 cm3 of sodium hydroxide solution
• 1. 1 Mole Ratio


  • 20.0 cm of 0.5 mol/dm3 sulfuric acid was needed to neutralise 25.0 cm3 of sodium hydroxide solution