Chapter 11

• pH


  Power of hydrogen ion concentration
• pH


  Inversely related to [H+]
• pH scale


  • 1
  • Strong acid
  • 3
  • Weak acid
  • 7
  • Neutral
  • 8-10
  • Weak base
  • 11-14
  • Strong base
• Strong acid


  • HCl, HNO3
• Weak acid


  • Citric acid, lactic acid, methanoic acid, ethanoic acid
• Neutral


  • Water, NaCl solution
• Weak base


  • NH3, NH2OH, soap
• Strong base


  • NaOH, KOH (caustic soda, potash)
• Litmus


  Indicator that changes colour in the presence of acids and bases
• Litmus colour changes


  • Red
  • Purple
  • Blue
• Neutral


  Neither acidic nor basic
• Universal indicator


  Indicator that shows a full range of colours across the pH scale
• Types of substances


  • Strong acid
  • Weak acid
  • Neutral
  • Weak base
  • Strong base
• Indicators are made of organic dyes that change colour when the pH changes
• Indicators cannot be used in titration if they have too many colour changes
• Acid-base indicators change colour at specific pH ranges
• Acid-base indicators


  • Methyl orange
  • Phenolphthalein
  • Thymolphthalein
• Methyl orange changes colour from red to yellow to orange as pH increases
• Phenolphthalein changes colour from colourless to pink to colourless as pH increases
• Thymolphthalein changes colour from colourless to blue to colourless as pH increases
• The end point in an acid-base titration is the point where the indicator changes colour
• Alkalis


  Proton acceptors
• Alkalis


  Substances that dissolve in water to give solutions with a pH greater than 7
• Bases


  • Metal oxide
  • Metal hydroxide
  • Metal carbonate
  • Ammonia
• Soluble bases are called alkalis
• Alkalis


  • Sodium hydroxide (NaOH)
  • Potassium hydroxide (KOH)
• Properties of bases


  • Bitter taste
  • Soapy appearance
  • pH greater than 7
  • Can turn red litmus blue
  • Can react with acids to form salts (Neutralisation)
• Neutralisation


  1. Reaction between acids and alkalis (bases)

  2. Reaction is always exothermic

  3. Salts can be made from this reaction
• Metal oxides and non-metal oxides

  • Basic oxide
  • Amphoteric oxide
  • Acidic oxide
  • Neutral oxide
• Basic oxides


  • Na₂O
  • CaO
• Amphoteric oxides


  • Al2O3
  • ZnO
• Basic oxides


  • MgO
• Acidic oxides


  • CO2
  • SO2
  • NO
  • NO2
  • N₂O
• Neutral oxides


  • CO
• Some Common Properties of acids

  • Sour taste (sharp and tangy)
  • Corrosive
  • pH less than 7
  • Can turn blue litmus to red
  • Can react with metals and alkali to produce salts
  • Can react with carbonate and carbon dioxide is produced