Chemical calculations

• Moles

  The number of atoms, molecules or ions in a mole of a given substance is the Avogadro constant
• Oxidation

  When a substance gains oxygen
• Reduction

  When a substance loses oxygen
• Calculating moles

  Moles = Mass (g) / Mr
• Reactivity series of metals

  • Shows the metals in order of their reactivity
  • Metals above H2 in reactivity series react with acid to produce H2. The more reactive the metal is, the quicker and more violent reaction with acid occurs.
  • Metals below H2 don't react with acids.
  • Not all metals above H2 react with water - mostly Group I and II metals. Aluminium is the borderline case.
• Displacement reaction

  A reaction where a more reactive metal displaces a less reactive metal from a compound
• Limiting reactant

  • Reactant which gets used up, causing the reaction to stop
  • Determines the amount of product
• Unreactive metals are found in their natural state in Earth
• Extracting metals less reactive than carbon

  Reduction with carbon. Carbon displaces the metal in a metal oxide - gets oxidised to carbon oxides. Metal from the metal oxide gets reduced to the pure metal.
• Concentration

  Can be measured in mass per unit volume
• Extracting metals more reactive than carbon

  By electrolysis
• Oxidation

  Loss of electrons
• Calculating concentration

  Concentration (g/dm3) = Mass (g) ÷ volume (dm3)
• Reduction

  Gain of electrons
• Atom economy

  Measure of amount of reactants which end up as useful products
• Not always possible to obtain theoretical amount of product
• Equations describe the mass of a substance in a certain volume of solution
• Atom economy

  • Higher atom economy implies a 'greener' process
  • Lower atom economy produces waste products which need to be disposed of
  • The atom economy is likely to be lower, the more products there are
  • Higher atom economy is better for profits
  • Waste products can be expensive to remove
  • Raw materials need to be bought more regularly for low atom economy processes
• Reaction between metals and acids

  Metal + acid → salt + hydrogen

  Redox reaction, also a displacement reaction
• Metals that will react with acid

  • Those above hydrogen in the reactivity series
• Avogadro's constant: 6.02 x 10^23
• Neutralisation reaction

  Base + acid → salt + water
• 2 moles of lithium reacts with one mole of fluorine to produce 2 moles of lithium fluoride
• Reaction between metal carbonate and acid

  Metal carbonate + acid → salt + water + carbon dioxide
• Any other reactants are in excess
• Reaction between metal oxides and acids

  Metal oxide + acid → a salt + water
• Amount of product formed is directly proportional to amount of limiting reactant
• Room temperature and pressure (RTP)

  20°C and 1 atm
• Redox reaction

  A reaction where both oxidation and reduction occurs
• Volume of one mole of any gas at RTP

  24 dm3
• Calculations

  Volume of gas = (Mass of gas × 24) / Mr of gas
• At the same temperature and pressure, equal numbers of moles of any gas will occupy the same volume
• Calculating mass of product formed

  1. Calculate moles of limiting reactant

  2. Determine ratio of limiting reactant to product

  3. Find mass of product
• Where volume is in dm3 and the mass of the gas is measured in grams
• When magnesium reacts with hydrochloric acid, magnesium has been oxidised (Mg to Mg2+) and the hydrogen in HCl has been reduced (H+ to H2)
• Concentration of solutions

  Measured in moles per unit volume
• Forming a soluble salt

  React the excess acid with some insoluble chemical (e.g. metal oxide)

  1. Filter off the leftovers
  2. Crystallise the product
• Calculating concentration

  1. Moles / Volume

  2. Volume measured in dm3
• Equal number of atoms of each element on each side of the equation
• Acids and alkalis in aqueous solutions

  Acids produce hydrogen ions, alkalis produce hydroxide ions