C4

• Metal oxides


  Metals + oxygen -> metal oxides
• Oxidation


  Gain of oxygen
• Reduction


  Loss of oxygen
• Reactivity series


  • When metals react with other substances, metal atoms form positive ions
  • Reactivity of a metal is related to its tendency to form positive ions
  • Metals can be arranged in order of their reactivity in a reactivity series
• Metals in order of reactivity

  • Potassium
  • Sodium
  • Lithium
  • Calcium
  • Magnesium
  • Zinc
  • Iron
  • Copper
• Reactions of acids with metals

  1. Acid + metal -> salt + hydrogen

  2. These are redox reactions - one substance is reduced and another is oxidised

  3. Identify which substances are oxidised and reduced by looking at electrons gained and lost (following OIL RIG)
• Reactions of metals with water

  • Potassium: violent
  • Sodium: very quick
  • Lithium: quick
  • Calcium: more slow
• Redox reaction


  A reaction where one substance is reduced and another is oxidised
• Reactions of metals with dilute acid

  • Calcium: very quick
  • Magnesium: quick
  • Zinc: fairly slow
  • Iron: more slow
  • Copper: very slow
• Neutralisation of acids and salt production

  1. Acid + alkali -> salt + water

  2. Acid + base -> salt + water

  3. Acid + metal carbonate -> salt + water + carbon dioxide
• Non-metals hydrogen and carbon are often included in the reactivity series
• Salt produced in alkali and base reactions

  • Depends on the acid used:
  • Hydrochloric acid (HCl) produces chlorides (XCl)
  • Nitric acid (HNO3) produces nitrates (XNO3)
  • Sulfuric acid (H2SO4) produces sulfates (XSO4)
  • Also depends on the positive ion in the base, alkali or carbonate (the metal X)
• Displacement


  A more reactive metal can displace a less reactive metal from a compound
• Gold is very unreactive and is found in the Earth as the metal itself
• Electrolysis


  The process of breaking down an ionic substance into its elements by passing an electric current through it
• Most metals are found as compounds that require chemical reactions to extract the metal
• The process of electrolysis

  1. Ionic substance is melted or dissolved

  2. Ions are free to move about

  3. Current is passed through the molten or solution

  4. Substance is broken down into elements
• The charges on the positive ion from the base/alkali/carbonate and the negative ion from the acid must add up to zero
• Reduction


  Involves the loss of oxygen
• Cathode


  The negative electrode
• Making soluble salts


  1. Add the chosen solid insoluble substance to the acid, the solid will dissolve

  2. Keep adding until excess solid sinks to the bottom, indicating the acid has been neutralised

  3. Filter out excess solid, evaporate some water, then leave the rest to evaporate slowly (crystallisation)
• OIL RIG


  Oxidation Is Loss and Reduction Is Gain (of electrons)
• Anode


  The positive electrode
• What happens during electrolysis

  1. Positively charged ions move to the cathode

  2. Negatively charged ions move to the anode

  3. Ions are discharged at the electrodes producing elements
• Writing ionic equations


  1. If sodium is oxidised, it has lost an electron, leaving it with a +1 charge, so the ionic equation is: Na -> Na+ + e-

  2. If sodium +1 ion is reduced, it has gained an electron, leaving it with a charge of zero, so the ionic equation is: Na+ + e- -> Na

  3. The charges on each side of the equation should add up to the same number
• pH scale


  • Measures the acidity or alkalinity of a solution
  • pH 7 is neutral
  • pH < 7 is acidic
  • pH > 7 is alkaline
• Electrolysis of molten ionic compounds

  1. Metal is produced at the cathode

  2. Non-metal is produced at the anode
• Neutralisation reaction


  H+(aq) + OH-(aq) -> H2O(l)
• Titration


  1. Wash burette with dilute HCl and water

  2. Fill burette to 100cm3 with acid

  3. Use 25cm3 pipette to add 25cm3 of alkali to conical flask

  4. Add indicator to conical flask

  5. Add acid from burette to alkali until end-point is reached (as shown by indicator)

  6. The titre is the difference between the first and second burette readings

  7. Repeat to gain more precise results
• Titration calculations


  • 1dm3 = 1000cm3
  • One mole of a substance in grams is the same as its relative atomic mass in grams
• Calculating concentration from titration


  Convert volumes to dm3

  2. Work out moles of NaOH

  3. Use mole ratio from equation to work out moles of HCl

  4. Calculate concentration = moles / volume
• Strong acid


  Completely ionised in aqueous solution (e.g. HCl, HNO3, H2SO4)
• Weak acid


  Partially ionised in aqueous solution (e.g. ethanoic, citric, carbonic acids)
• Strength of acid


  The stronger the acid, the lower the pH (for a given concentration of aqueous solutions)
• pH decreases by 1 unit


  H+ concentration increases by a factor of 10
• Strong/weak and concentrated/dilute are not the same - strong/weak refers to H+ ion concentration, concentrated/dilute refers to amount of substance in a given volume
• Metals extracted by electrolysis

  • Metals more reactive than carbon (e.g. aluminium)
  • Large amounts of energy used to melt compounds and produce electrical current
• Aluminium extraction by electrolysis

  • Molten mixture of aluminium oxide and cryolite
  • Carbon used as positive electrode (anode)
  • Positive electrodes need to be continually replaced
• Metals that react with carbon can also be extracted by electrolysis
• Electrolysis of aqueous solutions

  1. Ions discharged depend on relative reactivity of elements

  2. Hydrogen produced at cathode unless metal less reactive than hydrogen

  3. Halide ion or oxygen produced at anode depending on ions present