Acids, bases, Salts

• Acids contain hydrogen ions (H+)
• Alkalis (or bases) contain Hydroxide ions (OH-)
• Neutralisation 


  When an acid is added to an alkali the H+ ions combine with the OH- ions forming water, neutralising the pH
• Strong acids 


  Essentially 100% ionised in a solution
• Weak acids 


  Ionises very little in a solution
• Acids react with water forming ions
• Concentrated Solution


  Contains a large amount of acid in a given volume
• Dilute Solution 


  Contains a small amount of acid in a given volume
• pH scale 


  gauges the amount of hydrogen ions in a solution
• Neutralisation Reaction 


  When an acid is neutralised a salt is formed and all products are neutral. These reactions are also exothermic (temperature increases). The highest temperature reached is the point of neutralisation (pH 7)
• Metal + acid = Salt + Hydrogen
• Metal Oxide (base) + Acid = Salt + Water
• Metal Hydroxide (Alkali) + Acid = Salt + Water
• Metal Carbonate + Acid = Salt + Water + Carbon dioxide
• Hydrochloric acid

  Chloride salt
• Sulfuric acid

  Sulfate salt
• Nitric Acid

  Nitrate salt
• Ethanoic acid

  Ethanoate salt
• Base 


  Oxide
• Alkali 


  Produces hydroxide ions (OH-) in aqueous solutions with a pH range between 7 and 14. Alkalis are water soluble bases
• Reaction of an acid and a metal

  • This reaction produces hydrogen gas
  • Produces bubbles (fizzing)
  • More bubbles = more reactive
• Carbonate Test


  When acid reacts with a carbonate fizzing is observed due to Carbon dioxide
• Carbon dioxide test

  • Carbon dioxide causes bubbling/fizzing during reaction
  • It can be detected using limewater
  • Turns milky white when carbon dioxide is bubbled through it
• Testing for sulfate ions

  1. Detected using barium chloride solution
  2. Test solution is acidified using a few drops of dilute hydrochloric acid then a few drops of barium chloride solution
  3. A white precipitate of barium sulfate forms if sulfate ions are present
• Preparation of soluble salts

  1. Add copper (II) oxide in excess (until no more will react) so that all sulfuric acid has reacted.

  Observation = colour change from colourless to blue, black solid sinks to bottom

  2. Filter to remove excess copper (II) oxide from blue copper (II) sulfate solution, excess copper oxide is left in filter paper

  3. Heat copper (II) sulfate solution to evaporate some of the water

  4. Leave to cool and crystals will form
• This can also be done with copper (II) carbonate and sulfuric acid


  Differences: Green solid instead of black, Bubbling due to carbon dioxide
• Titration Method

  1. Use the pipette to add 25.0cm of alkali to a clean conical flask
  2. Add a few drops of indicator
  3. Fill the burette with acid and note the starting volume
  4. Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix
  5. Stop adding the acid when the indicator changes colour, note the final volume
  6. Repeat steps 1 to 5 without indicator and using the volume acid you found
• If the volume of the unknown is less than the known then the unknown must be more concentrated
• If the volume of the unknown is more than the known then the unknown must be less concentrated
• Metal hydroxide is an alkali which means its soluble in water
• Neutralisation 


  The reaction in which an acid and a base react together to form a salt and water.
• Precipitation reaction


  A reaction in which solutions react to form an insoluble solid
• Acid


  produces hydrogen ions (H+) in aqueous solutions with a pH range between 0 and 7. Acids will react with metals to produce a salt and hydrogen and will react with carbonates to produce a salt, water and carbon dioxide
• Titration


  A technique used where a solution of known concentration is used to determine the concentration of an unknown solution
• Strong acid 


  An acid which is completely ionised in a solution so that nearly all the H+ ions are released
• Weak acid 


  An acid which is only partially ionised in a solution this means only a small number of H+ ions are released