Acids x Bases x Salt

• 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
• Metals, bases and certain metal carbonates

  • Insoluble in water
• 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
• Stage 2

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

  2. The excess solid remains in the filter paper

  3. The salt solution passes through into the evaporating basin
• Stage 3

  1. The salt crystals are collected from the solution by evaporation

  2. The solution is heated to evaporate the water

  3. Large crystals - evaporate water slowly near a radiator or window ledge

  4. 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. A titration is used to produce a salt from an acid and alkali

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

  3. Add a few drops of indicator to the flask

  4. Place the flask onto a white tile

  5. Fill the burette with acid

  6. Slowly add the acid from the burette to the alkali until the indicator changes colour

  7. Record the volume of acid added to the flask

  8. Repeat steps 1-6 without using the indicator and adding the same volume of acid from the burette
• The colour change will depend on which indicator is used to carry out the titration
• 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
• Indicators


  Substances that change colour when they are added to acids and alkalis
• Litmus


  • The most well-known indicator
  • Turns red in acid and blue in alkalis
• Universal indicator


  • Most commonly used in the laboratory
  • Changes colour to show the pH of the solution
• Acidic


  pH < 7
• Neutral


  pH 7
• Alkaline


  pH > 7
• Acids and alkalis are commonly used both in industry and at home
• Acids


  Produce hydrogen ions, H+, when they dissolve in water
• Base


  • Chemically opposite to an acid
  • A base that dissolves in water is called an alkali
• Alkalis


  Produce hydroxide ions, OH–, when they dissolve in water
• Dangerous acids and alkalis have the corrosive hazard warning symbol on their containers
• Neutralisation


  Acid + alkali → salt + water
• Neutralisation

  H+(aq) + OH–(aq) → H2O(l)
• The name of the salt produced depends upon the acid and alkali that react
• Acids and metals

  Acid + metal → salt + hydrogen
• The hydrogen causes bubbling during the reaction and the reaction is exothermic
• The more reactive the metal, the faster the reaction is, resulting in more bubbling and a bigger temperature rise
• Acids and alkalis/bases

  Acid + alkali → salt + water
• The reactions of acids with alkalis and bases are exothermic
• Acids and carbonates

  Acid + carbonate → salt + water + carbon dioxide
• The carbon dioxide causes bubbling during the reaction and the reaction is exothermic