science f2 chap6

• Acid

  • pH value less than 7
  • Tastes sour
  • Corrosive
  • Turns blue litmus paper red
  • Reacts with metals to produce hydrogen gas
• Alkali

  • pH value more than 7
  • Tastes bitter
  • Corrosive
  • Turns red litmus paper blue
  • Does not react with metals
• Acidic substances


  • Vinegar
• Alkaline substances


  • Soap
• Indicator

  A colouring or a mixture of different colourings that changes colour based on the substance tested
• Phenolphthalein


  • Acid & neutral: Colourless
  • Alkali: Pink
• Universal Indicator


  • Acid: Red
  • Neutral: Green
  • Alkali: Blue
• Methyl orange


  • Acid: Red
  • Neutral and Alkali: Yellow
• Blue litmus paper


  • Acid: Red
  • Neutral and Alkali: Blue
• Red litmus paper


  • Acid and neutral: Red
  • Alkali: Blue
• pH scale


  • Used to show the strength of acids or alkalis
  • The lower the pH value, the stronger the acid
  • The higher the pH value, the stronger the alkali
• Uses of Acids

  • Tartaric acid - Tartaric acid
  • Fizzy drink - Carbonic acid
  • Car battery - Sulphuric acid
  • Pickle - Vinegar
• Uses of Alkalis

  • Soap - Potassium hydroxide
  • Fertiliser - Ammonia
  • Detergent - Sodium hydroxide
  • Antacid pills - Magnesium hydroxide