Chemical changes

• Metal oxides


  Metals + oxygen → metal oxides
• Oxidation


  Metals gain oxygen
• Reduction

  Loss of oxygen
• The reactivity series

  • Potassium
  • Sodium
  • Lithium
  • Calcium
  • Magnesium
  • Zinc
  • Iron
  • Copper
• When metals react with other substances

  Metal atoms form positive ions
• Reactivity of a metal

  Tendency to form positive ions
• Elements and their reaction with water

  • Potassium: violent
  • Sodium: very quick
  • Lithium: quick
  • Calcium: more slow
• Elements and their reaction with dilute acids

  • Calcium: very quick
  • Magnesium: quick
  • Zinc: fairly slow
  • Iron: more slow
  • Copper: very slow
• Non-metals hydrogen and carbon are often included in the reactivity series
• A more reactive metal can displace a less reactive metal from a compound
• Gold

  Very unreactive, found in the Earth as the metal itself
• Extraction of metals

  Metals less reactive than carbon can be extracted from their oxides by reduction with carbon
• Reduction

  Involves the loss of oxygen
• OIL RIG

  Oxidation Is Loss and Reduction Is Gain (of electrons)
• Writing ionic equations

  1. If sodium is oxidised, it has lost an electron, leaving it with a +1 charge

  2. If sodium +1 ion is reduced, it has gained an electron, leaving it with a charge of zero
• The charges on each side of the ionic equation should add up to the same number
• Identifying oxidation and reduction in an equation

  1. Look at the changes in the elements

  2. Oxidation is loss of electrons

  3. Reduction is gain of electrons
• Acids react with some metals to produce a salt and hydrogen
• Redox reactions

  One substance is reduced and another substance is oxidised
• Identifying oxidation and reduction in a redox reaction


  Look at electrons gained and lost using OIL RIG
• Acids are neutralised by alkalis (e.g. soluble metal hydroxides) and bases (e.g. insoluble metal hydroxides and metal oxides) to produce salts and water
• Acids are neutralised by metal carbonates to produce salts, water and carbon dioxide
• Salts produced

  Depend on the acid and the positive ions in the base, alkali or carbonate
• The charges on the positive ion from the base/alkali/carbonate and the negative ion from the acid must add up to zero
• Soluble salts

  Can be made from acids by reacting them with solid insoluble substances, such as metals, metal oxides, hydroxides or carbonates
• Making soluble salts

  1. Add the chosen solid insoluble substance to the acid

  2. Keep adding until excess solid sinks to the bottom

  3. Filter out excess solid leaving the salt solution

  4. Evaporate some water, then leave the rest to evaporate slowly
• pH scale

  • Measures the acidity or alkalinity of a solution, 0-14
  • pH 7 is neutral
  • pH < 7 is acidic
  • pH > 7 is alkaline
• Acids

  Produce H+ ions in aqueous solutions
• Alkalis

  Produce OH- ions in aqueous solutions
• H+ (aq) + OH- (aq) → H2O(l) is the ionic equation of any neutralisation reaction
• Titration

  1. Wash burette

  2. Fill burette with acid

  3. Use pipette to add alkali to conical flask

  4. Add indicator

  5. Add acid from burette until end-point

  6. Titre is the difference in burette readings
• Titration calculations

  1. Convert volumes to dm3

  2. Work out moles of NaOH

  3. Mole ratio from equation

  4. Work out concentration
• Strong acid

  Completely ionised in aqueous solution
• Weak acid

  Partially ionised in aqueous solution
• As the pH decreases by one unit, the H+ conc. of the solution increases by a factor of 10
• Strong/weak vs concentrated/dilute

  Strong/weak refers to H+ ion conc, concentrated/dilute refers to amount of substance
• Electrolysis

  Breaking down of an ionic substance in the molten or dissolved state by passing an electric current through it
• Electrolysis of molten ionic compounds

  Metal produced at cathode, non-metal produced at anode
• Extracting metals by electrolysis

  Used for metals more reactive than carbon, requires large amounts of energy
• Electrolysis of aqueous solutions

  1. Hydrogen produced at cathode unless metal is less reactive than hydrogen

  2. Halide ions or oxygen produced at anode depending on what's present