Acids and Bases

• pH Scale


  Goes from 0 to 14
• pH Scale


  • Measure of how acidic or alkaline a solution is
• The lower the pH of a solution

  The more acidic
• The higher the pH of a solution

  The more alkaline
• A neutral solution (e.g. pure water) has a pH of 7
• pH indicator


  A substance that changes colour depending on the pH of a solution
• Wide range pH indicators


  • Substances that gradually change colour as pH changes
  • Useful for estimating the pH of a solution
• Wide range pH indicator


  • Universal indicator
• pH meter


  An electronic device that can accurately measure the pH of a solution
• Acids have a pH less than 7
• Bases/Alkalis have a pH greater than 7
• Alkalis are bases that dissolve in water to form solutions with a pH greater than 7
• Neutralisation reaction


  Acid + Base → Salt + Water
• The products of neutralisation reactions have a pH of 7, meaning they are neutral
• Using an indicator to determine neutralisation point


  1. Add acid/alkali gradually

  2. Indicator changes colour when neutralisation is complete

  3. Use Universal indicator to get pH 7
• Hydrogen (H) ions react with hydroxide (OH) ions to produce water