C2.1

• Pure substance


  A single element or compound, not mixed with any other substance
• Pure substance (everyday language)


  Substance that has had nothing added to it, so it is unadulterated and in its natural state
• Pure substances


  Melt and boil at specific temperatures
• Impure substances


  Melt and boil over a range of temperatures
• Relative formula mass


  Sum of the relative atomic masses of the atoms in the numbers shown in the formula
• Relative formula mass (in a balanced chemical equation)

  Sum of Mr of reactants in quantities shown = sum of Mr of products in quantities shown
• Relative atomic mass


  Ratio of the average mass of one atom of an element to 1/12th of the mass of an atom of carbon-12
• Relative molecular mass


  Ratio of the average mass of one molecule of an element or compound to 1/12th of the mass of an atom of carbon-12
• Relative formula mass


  Weighted average of the masses of the formula units relative to 1/12th of the mass of a carbon-12 atom
• Empirical formula


  Simplest whole number ratio of atoms of each element in a molecule
• Formulation


  Mixture that has been designed as a useful product
• Useful materials that are formulations of mixtures

  • Food and drink products
  • Medicines
  • Sunscreens
  • Perfumes
  • Paints
• Alloy


  Metal mixed with small amounts of similar metals to make it harder for everyday use
• Filtration


  Separate precipitate from salt solution
• Crystallisation


  1. Warm solution to evaporate solvent

  2. Allow solution to cool to grow crystals

  3. Collect and dry crystals
• Simple distillation


  Separate solvent from solution by heating to evaporate solvent, then condense vapour
• Fractional distillation


  Separate pure liquids from a mixture of liquids with different boiling points by heating and condensing at different temperatures
• Chromatography


  Separation technique involving a stationary phase and a mobile phase, separation depends on distribution between the phases
• Paper chromatography


  Stationary phase = paper, mobile phase = solvent
• Thin layer chromatography (TLC)

  Stationary phase = thin layer of inert substance on flat surface, mobile phase = solvent
• Rf value


  Distance moved by substance / distance moved by solvent
• Different compounds have different Rf values in different solvents, which can be used to help identify the compounds
• Compounds in a mixture separate into different spots but a pure compound will produce a single spot
• Gas chromatography


  Mobile phase = inert carrier gas, stationary phase = liquid / solid on solid support, separation depends on solubility in gas