C2 - Material Choices

C2 - Material Choices

1. Natural & Synthetic Materials

   • Materials are chemicals or mixtures of chemicals - e.g. metals, ceramics & polymers
   • Natural Materials - come from living things, for example...
     • - cotton & paper (plants)
     • - silk & wool (animals)
   • Synthetic Materials - produced by chemical synthesis, for example...
     • - crude oil is refined to produce fuels - only a small proportion of crude oil is used for chemical synthesis

2. Crude Oil & Fractional Distillation

   • Crude oil - a mixture of hydrocarbons
     • Hydrocarbons - compounds that are made from carbon & hydrogen atoms
       • - some hydrocarbons have small molecules but others have longer chain molecules
   • Fractional Distillation - separates crude oil into fractions
     • - hydrocarbons in 1 fraction have similar boiling points
     • Different fractions have different boiling points
       • Different fractions include...
         • - bitumen
         • - fuel oil
         • - diesel
         • - kerosene/paraffin
         • - naphtha
         • - petrol
         • - refinery gases
     • 1 - crude oil is heated to evaporate hydrocarbons
       • 2 - the vapour passes into fractionating column near the bottom and cools as it rises
         • 3 - each fraction condenses to a liquid + runs off when cooled below its boiling point
           • 4 - any remaining gases leave tower at the top - are used as gaseous fuels

3. Explaining Boiling Points

   • Intermolecular forces = all molecules have forces holding them together
   • The longer the hydrocarbon molecules the stronger the intermolecular forces
     • Stronger intermolecular forces need more energy to over power them - a higher temperature is needed to boil longer hydrocarbon fractions

4. Properties of Materials

   • Different solid materials have different properties, for example, they...
     • - have different melting points & densities
     • - can be strong or weak (in tension or compression)
     • - can be rigid or flexible, hard or soft
     • - will be better suited to certain uses

5. Polymerisation

   • Small hydrocarbon molecules (monomers) are joined together to make long molecules (polymers)
     • e.g. polymer poly(ethene) - polythene - made from ethene monomers
     • During a chemical reaction, the number of atoms of each element in the products must be the same as in the reactants
     • Different monomers make different polymers with different properties
   • Polymerisation can be used to create a variety of materials which have different properties
     • Many traditional & natural materials have been replaced by polymers due to their superior properties
       • e.g. carrier bags used to be made from paper - now made from polythene because they are stronger & waterproof
       • e.g. window frames were made of wood - now made of polychloroethene because it's unreactive so doesn't rot

6. Molecular Structure of Materials

   • Properties of solid materials depend on the arrangement of their particles & how they are held together
     • Natural Rubber - made up of long-chain molecules held together by strong covalent bonds (long molecules slide over one another - materials stratches)
       • - Is flexible, has low melting point - little energy needed to separate molecules
   • Vulcanised Rubber - made up of tangled molecules - atoms within chains held together by strong covalent bonds
     • Molecules have cross-links - strong covalent bods between long-chain molecules
       • - Is rigid & hard to stretch as molecules wont slide, needs a lot of energy to separate molecules - high melting point

7. Modification of Polymers

   • Increasing chain length - more contact so stronger forces between molecules (make plastic stronger)
   • Plasticizers - added to polymers - makes them softer & more flexible
     • Plasticizer molecules sit between polymer molecules + forces them apart
       • Plastisized PVC - used in children's toys
         • Unplasticized PVC (uPVC) - used in window frames
   • Chrystalline polymer - molecules packed closely together - stronger intermolecular forces, denser, higher mp

8. Nanotechnology

   • Production, study & control of tiny particles on a nanoscale
   • Nanometre = one millionth of a millimetre
   • Nanoparticles - can be used to modify properties of materials - especially polymers
     • Silver nanoparticles - used to give fibres in clothes antibacterial properties
       • (e.g. stop socks smelling)
     • Carbon nanotubes - added to sports equipment to make them lighter & stronger
       • (e.g. tennis rackets, gold clubs)
     • New use could cause health problems - inhaled easily