purity and seperating mixtures

• mixture - 2 or more atoms held together by chemical bonds
• compound - a substance that contains 2 or more elements that are chemically bonded together
• pure substance - only contains one type of element or compound
• pure substances melt and boil at specific temperatures. therefore to identify impure substances, it would have irregular melting and boiling points.
• impure substances - the melting point is lower and the boiling point is higher
• formulation - contain specific amounts difference components
• solvent - the liquid
• solute - the solid
• pure substances


  pure substances melt and boil at specific temperatures. impure substances melt and boil over a range of temperatures
• relative formula mass: Mr


  sum of the relative atomic masses [the big numbers].
• relative molecular mass: ratio of the average mass of one MOLECULE of an element or compund to 1/12 th of the mass of an atom of carbon - 12
• relative atomic mass: ratio of the average mass of one ATOM of an element to 1/12 th of the mass of one atom on carbon - 12
• relative formula mass: weighted average of the masses of the formula units
• empirical formula: simplest whole number ratio of atoms of each element in a molecule
• formulation: mixture that has been designed as a useful product
• formulation


  these are made by mixing the components in carefully measured quantities to ensure that the product has the right properties.

  examples are food, drink, medicines, sunscreens, perfumes and paints
• alloys


  most metals in everyday uses are alloys/ pure copper, gold, iron and aluminium are too soft for everyday use and so are mixed with small amount of similar metals to make them harder [ for everyday use ]
• filtration


  • if you have a produced an insoluble salt / precipitate, and you want to seperate the salt from the solution

  1. filter the solution with filter paper and a funnel, leaving behind the precipitate.
  2. you can put it in a water bath to crystallise
• crystallisation


  • if you have produced a SOLUBLE salt

  1. warm the solution, allowing the solvent to evaporate
  2. allow it to cool
  3. for speed, put them in a water bath so they can crystallise
• simple distillation


  • used to separate a solvent from a solution
  • when the solution is heated, solvent vapout evaporates from the solution. the gas moves away and is cooled and condensed in a condenser
  • this only works if one has a significantly higher boiling point than the other.
  • at the end, in the conical flask: the solution, in the beaker: solvent
• fractional distillation


  • used to separate a pure liquid from multiple liquids [e.g. crude oil]
  • gradually heat the flask, at different boiling points, different liquids will evaporate
  • the liquid with the lowest boiling point evaporates first, so it rises through the fractionating column [ with glass rods and a thermometer and a bung] and condenses in the condenser.
  • this will be collected in a beaker on the bottom of the condenser
• paper chromatography


  • used to separate mixtures and give information to help identify substances
  • involves a stationary [unmoving] phase and a mobile [moving] phase
  • stationary - paper
  • mobile - solvent
• thin layer chromatography


  • used to separate mixtures and give information to help identify substances
  • involves a stationary [unmoving] phase and a mobile [moving] phase
  • stationary - thin layer of inert substance
  • mobile - solvent
• Rf value = distance moved by substance / distance moved by solvent
• gas chromatography


  • mobile - inert carrier gas
  • stationary - liquid / solid [lined on tube]

  
• retention time: a measure of the time taken for a solute to pass through a chromatography column