Topic 3 - Chemical Changes

• pH scale


  • Shows how acidic or alkaline a substance is
  • 0-6 is acidic
  • 7 is neutral
  • 8-14 is alkaline
• Alkali


  • Soluble base
  • Can neutralize an acid
• Dissociation


  1. Acids split up into hydrogen ions (H+)in solution

  2. Alkalis split up into hydroxide ions (OH-)in solution
• Strong vs Weak acids/alkalis

  • Strong completely dissociate into ions
  • Weak only partially dissociate
• Concentrated vs Dilute


  • Concentrated has a lot of the substance
  • Dilute has only a small amount of the substance
• Common acids


  • Hydrochloric acid (HCl)
  • Nitric acid (HNO3)
  • Sulfuric acid (H2SO4)
• Common bases/alkalis


  • Sodium hydroxide (NaOH)
  • Potassium hydroxide (KOH)
  • Calcium hydroxide (Ca(OH)2)
• Indicator


  • Used to test if a substance is acidic or alkaline
  • Methyl orange, phenolphthalein, red/blue litmus paper, universal indicator
• Testing for gases


  1. Hydrogen - squeaky pop with lit splint

  2. Carbon dioxide - turns limewater cloudy

  3. Oxygen - relights glowing splint
• Neutralization


  1. Acid and base react to form a salt and water

  2. Resulting solution has pH 7 (neutral)
• Acid reactions


  • Acid + metal oxide/hydroxide = salt + water
  • Acid + metal = salt + hydrogen
  • Acid + metal carbonate = salt + water + carbon dioxide
• Salt


  • Product formed when an acid and base react
  • Can be soluble or insoluble
• Making copper sulfate


  1. React copper oxide with sulfuric acid

  2. Add excess copper oxide

  3. Filter off unreacted copper oxide

  4. Crystallize to get pure copper sulfate
• Titration


  • Used to control the exact amount of reactant added
  • Uses a burette to gradually add drops of one reactant to the other
• Electrolysis


  • Using electricity to split up ionic compounds
  • Positive ions move to cathode, negative ions move to anode
• Oxidation and Reduction in electrolysis

  1. Oxidation is loss of electrons at anode

  2. Reduction is gain of electrons at cathode
• Electrolysis of dissolved ionic compounds

  1. Less reactive ion is given off at electrodes

  2. Hydrogen given off at cathode, chlorine given off at anode
• Half equations can be used to describe the reactions at each electrode during electrolysis