C3

• Mole (mol)


  A measure of the number of particles (atoms, ions or molecules) contained in a substance, one mole of any substance contains the same number of particles (6.02 x 10^23 - Avogadro's constant)
• Mass of one mole of a substance

  The mass in grams is equal to the relative atomic mass or relative formula mass
• One mole of sodium atoms has a mass of 23.0 g
• Calculating the amount of substance (number of moles) in a given mass of a substance


  Amount = mass of substance / formula mass
• Balanced equation


  Shows the number of moles of the products and reactants
• Balanced equations can be used to calculate the mass of the reactants and products
• Limiting reactant


  The reactant that is completely used up during the reaction, stopping the reaction from going any further
• Excess reactant


  The reactant that is not used up in the reaction
• At room temperature and pressure, one mole of any gas takes up a volume of 24 dm³
• Concentration of a solution

  Amount of substance (mol) / Volume (cm³)
• Neutralisation


  Reaction between an acid and an alkali to form a neutral solution
• Titration


  1. Accurate technique used to find how much acid is needed to neutralise an alkali

  2. Measure out 25 cm³ of alkali using a pipette

  3. Add 3-5 drops of indicator (e.g. methyl orange)

  4. Carefully add acid from a burette until the indicator just changes colour (end point)

  5. Record the volume of acid used
• Atoms are never lost or gained in a chemical reaction, they are just rearranged
• Percentage yield


  Actual mass of product / Theoretical mass of product x 100
• Atom economy


  Total Mr of useful product / Total Mr of all products x 100
• Ethanol production


  Can be produced by hydration or fermentation
• In a chemical reaction, the total mass of the reactants equals the total mass of the products (conservation of mass)
• Balancing a chemical equation

  Use half-equations to show what happens to each reactant, including the transfer of electrons
• Spectator ions


  Ions not involved in the reaction that are not included in the balanced equation
• Relative formula mass (Mr)


  The sum of the relative atomic masses of all the atoms and numbers shown in the formula (not including the big numbers)
• When a reaction is carried out in an open system, the total mass can appear to change due to gases entering or leaving
• Factors to consider when choosing a reaction pathway

  • Cost of reactants
  • Percentage yield
  • Rate of reaction
  • Equilibrium position
  • Usefulness of by-products
• Oxidation


  A substance gains oxygen
• Reduction


  A substance loses oxygen
• Oxidation and reduction always occur together
• Metal oxides


  • Formed when metals react with oxygen, e.g. magnesium reacting with oxygen to form magnesium oxide
• Reducing metal oxides


  Heat metal oxide with carbon to remove oxygen, e.g. heating lead oxide with carbon