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+)

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

  • Strong - completely dissociate
  • Weak - partially dissociate
• Neutral pH has equal concentrations of H+ and OH- ions
• Common acids


  • Hydrochloric acid (HCl)
  • Nitric acid (HNO3)
  • Sulfuric acid (H2SO4)
• Common 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, litmus paper, universal indicator
• Testing for gases


  1. Hydrogen - squeaky pop with lit splint

  2. Carbon dioxide - bubbled through, turns limewater cloudy

  3. Oxygen - relights glowing splint
• Neutralization


  Reaction of an acid and base to form a salt and water
• Acid reactions


  1. Acid + metal oxide/hydroxide = salt + water

  2. Acid + metal = salt + hydrogen

  3. Acid + metal carbonate = salt + water + carbon dioxide
• Salt


  Product formed when an acid and base react
• Solubility of salts


  • Soluble - nitrates, most chlorides, most sulfates
  • Insoluble - silver/lead chlorides, lead/barium/calcium sulfates, most carbonates, most hydroxides
• 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


  Controlled addition of acid/base to determine exact amount needed
• Electrolysis


  Using electricity to split up ionic compounds
• Electrolysis setup


  1. Positive anode, negative cathode

  2. Ionic compound as electrolyte (molten or dissolved)
• Oxidation and Reduction


  • Oxidation - loss of electrons at anode
  • Reduction - gain of electrons at cathode
• Electrolysis of dissolved ionic compounds

  Less reactive ion is given off (e.g. hydrogen over sodium, chlorine over hydroxide)
• Half equations describe what happens to each ion during electrolysis