Acids and bases

• Acid


  A chemical substance with a pH of below 7
• Base


  A substance that is the chemical opposite of an acid (pH of greater than 7)
• Bases


  • Sodium fluoride in toothpaste
  • Sodium hydroxide (NaOH)
  • Calcium carbonate (CaCO3)
  • Limewater (Ca(OH)2)
• Alkali


  A base that is soluble in water
• Neutral


  Chemical substances that do not have the properties of acids or bases
• Acidic substances


  • Vinegar
  • Citrus fruits
• Basic substances


  • Hand soap
  • Bleach
• Symbol used to show a substance is corrosive
• Handling corrosive substances safely

  1. Wear gloves

  2. Wipe up any spills immediately
• pH scale


  Used to record how acidic or alkaline a solution is, goes from 0 to 14
• pH scale


  • Substance with pH below 7 is acidic
  • Substance with pH of 7 is neutral
  • Substance with pH above 7 is alkaline
• Indicator


  A substance that changes colour to show if a solution being tested is an acid or a base
• Litmus indicator


  Changes colour in an acid or base, often used in paper form
• Litmus indicator


  • Acid turns blue litmus red
  • Base turns red litmus blue
  • Neutral causes no change to red or blue litmus
• Universal indicator


  A mixture of dyes that change colour when they come into contact with an acid or base, shows concentration
• The pH scale goes from 0 to 14
• Measuring pH of a substance


  1. Universal indicator paper

  2. pH meter
• Neutralisation


  When an acid and a base react, they produce a salt and water solution (pH 7)
• Acidic soil


  Farmers spread powdered limestone (calcium carbonate) to bring pH closer to neutral
• Plaque is acidic


  Toothpaste is alkaline and removes plaque
• Acid added to a base

  pH will decrease
• Key terms


  • Acid
  • Base
  • Alkali
  • Neutral
  • pH scale
  • Indicator
  • Litmus indicator
  • Universal indicator
  • Neutralisation