Acid and bases

• pH scale


  Measure of how acidic or alkaline a solution is
• pH scale


  • Ranges from 0 to 14
  • Lower pH = more acidic
  • Higher pH = more alkaline
  • Neutral substance (e.g. pure water) has pH 7
• Neutral substances


  • Pure water
  • Normal rain
• Measuring pH of a solution


  1. Use indicator

  2. Indicator changes colour depending on pH

  3. pH meter can also be used
• Acid


  Substance that forms aqueous solution with pH less than 7
• Base


  Substance with pH greater than 7 that dissolves to form a solution
• Neutralisation reaction


  Acid + base → salt + water
• Skin is slightly acidic with pH around 5.5
• Lemon juice


  • Expected indicator colour
• pH 8


  Solution is alkaline