Purity and Seperating Mixture

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  • Purity and Separating Mixtures
    • Relative Formula Mass
      • RAM= Relative Atomic Mass.
      • RAM is the mean mass of an atom of an element compared to 1/12 mass of a carbon-12 atom.
      • Chemical formula states how many atoms of each element there are in a unit.
      • Relative Formula Mass= Mean mass of a substance compared to 1/12 of a carbon-12 atom.
        • RFM isn't found on the periodic table, so this is something you have to work out yourself.
    • Empirical Formula
      • Simplest whole-number ratio of the atoms of each element in a compound.
      • Numbers can be simplified by using the HCF.
      • The total number of atoms on the left hand side of an equation must be equal to the right.
    • Pure and Impure Substances
      • Pure- Something that has not been processed or changed.
        • Just one element or compound.
      • Impure- A mixture containing one or more element.
      • It is difficult to obtain pure It is difficult to substances. Many mixtures are useful materials.
      • Impure- Melting point is less than of pure substance.
        • Melts over a range of temperatures.
      • To determine melting point- Melt substance slowly and stir it as it melts.
    • Filtration and Crystallisation
      • Solution- One substance dissolves into another.
      • Solute- Substance that dissolves.
      • Solvent- Substance it dissolves in.
      • Soluble- Can dissolve in particular solvent.
      • Insoluble- Can't dissolve in particular solvent.
      • Filtration separates insoluble substance in the solid state from substances in the liquid state.
      • Filtration works as filter paper has tiny holes.
        • Larger grains don't pass through.
        • Smaller molecules pass through.
      • Crystallisation- heat the solution until it becomes saturated.
        • When the solution cools, the solubility decreases.
          • This forms crystals.
    • Distillation
      • SIMPLE distillation separates a solvent from a solution.
        • Relies on solvent having a lower boiling point than solute.
        • The solution is heated: solvent boils but solute doesn't.
        • Solvent escapes through gas state.
        • Solvent is then cooled down back to a liquid state in a condenser.
        • Used in labs.
      • FRACTIONAL Distillation- Separates TWO OR MORE substances from a mixture.
        • This is done through a fractioning column.
        • E.g: FD of ethanol-water mixture, ethanol vapour and water vapour both leave liquid mixture.
          • In the FC: vapours condense on the inside, heating it up.
            • When temp reaches boiling point of ethanol, ethanol vapour can't condense any more. Water can.
              • Water droplets fall back into flask, ethanol vapour is cooled down back to liquid state.
                • Ethanol the drips into collecting container.


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