chemical changes

• Oxidation


  Loss of electrons
• Reduction


  Gain of electrons
• Displacement reactions


  1. Metal ions reacting in terms of electrons being transferred

  2. Non-metal ions 'spectating'
• Zn


  Oxidised (lost electrons to become more positive)
• Cu2+


  Reduced (gained electrons to become neutral)
• Reactions of acid with metals are redox reactions
• Reactions of acid with metals


  Metal + acid salt + hydrogen
• Metals that will react with acids


  • All metals above hydrogen in the reactivity series
• Metals that will not react with acids

  • Metals below hydrogen in the reactivity series
• Acids are neutralised by alkalis (eg soluble metal hydroxides) and bases (eg insoluble metal hydroxides and metal oxides) to produce salts and water
• The particular salt produced in any reaction between an acid and a base or alkali depends on the acid used and the metal in the base or alkali
• Making soluble salts


  1. Solid insoluble substance (metal, metal oxide, hydroxide or carbonate) added to acid until no more reacts

  2. Excess solid filtered off to produce salt solution

  3. Salt solution crystallised to produce solid salt
• In neutralisation reactions between an acid and an alkali, hydrogen ions react with hydroxide ions to produce water
• pH scale


  Measure of acidity or alkalinity of a solution
• pH 7 is neutral, pH less than 7 is acidic, pH greater than 7 is alkaline
• Strong acid


  Completely ionised in aqueous solution
• Strong acids


  • Hydrochloric, nitric, sulfuric
• Weak acid


  Only partially ionised in aqueous solution
• Weak acids


  • Ethanoic, citric, carbonic
• For a given concentration, the stronger an acid, the lower the pH
• Concentrated acid


  More moles of acid per unit volume than a dilute acid
• Dilute acid


  Made by adding water to a concentrated acid
• As pH decreases by one unit, H+ concentration increases by a factor of 10
• If an acid is diluted 10 times, its pH will increase by one unit
• Universal indicator colours


  • Red pH 1-2 strong acid
  • Orange/yellow pH3-6 weak acid
  • Green pH7 neutral
  • Blue pH8-11 weak alkali
  • Purple pH 12-14 strong alkali
• Titrations


  1. Measure volumes of acid and alkali solutions that react completely

  2. If volume and concentration of one solution known, can calculate concentration of other
• Know the basic method for doing a titration
• Concentrations


  • 1.0 x 10-2
  • 2.0
  • 1.0 x 10-3
  • 3.0
  • 1.0 x 10-4
  • 4.0
  • 1.0 x 10-5
  • 5.0
  • 1.0 x 10-6
  • 6.0
• If an acid is diluted 10 times

  Its pH will increase by one unit
• Universal indicator colours


  • Red pH 1-2 strong acid
  • Orange/yellow pH3-6 weak acid
  • Green pH7 neutral
  • Blue pH8-11 weak alkali
  • Purple pH 12-14 strong alkali
• Titration


  1. Measure volumes of acid and alkali solutions that react

  2. Use a suitable indicator

  3. If volumes and concentration of one solution known, can calculate concentration of other
• Titration method


  • Alkali in burette
  • Acid in conical flask measured with 25cm3 pipette
  • Add alkali to acid until colour changes
  • Swirl conical flask
  • Add alkali dropwise towards end
  • Note final burette reading
  • Repeat until two readings within 0.1cm3
• Titration calculations


  1. Step 1: Calculate moles of substance with known volume and concentration

  2. Step 2: Use balanced equation to work out moles of other substance

  3. Step 3: Calculate concentration of second substance
• A pipette measures one fixed volume accurately, a burette measures variable volume
• Electrolyte


  Liquids and solutions able to conduct electricity due to free-moving ions
• Electrolysis


  1. Passing an electric current through ionic substances to break them down into elements

  2. Positive ions move to negative electrode (cathode)

  3. Negative ions move to positive electrode (anode)
• Reduction

  Gaining electrons
• Oxidation


  Losing electrons
• Electrolysis of molten salts


  1. Metals can be extracted from molten compounds

  2. Aluminium extracted by electrolysis of molten aluminium oxide and cryolite

  3. Cryolite lowers melting point to reduce energy costs
• Electrolysis of aqueous solutions

  1. Oxygen produced at anode unless halide ions present when halogen produced

  2. Hydrogen produced at cathode for reactive metal salts

  3. Metal produced at cathode for unreactive metal salts