C1 - Carbon chemistry

Fractional distillation:

• Order from top to bottom:
  • LPG, petrol, paraffin, diesel, heating oil, fuel oils, bitumen
• hydrocarbons in different fractions have differently sized molecules:
  • large molecules, like those of bitumen, have stronger intermolecular forces
  • a lot of energy is needed to break the forces between molecules which is why these have high boiling points and sink and exit at the bottom of the tower
  • smaller molecules like petrol have weaker intermolecular attractions and are easily broken
  • less energy is needed to break the forces so they have low boiling points and exit at the top of tower
• Problems:
  • oil producing nations set high prices, can be a problem for non oil producing nations
• Cracking: turns large alkane molecules into smaller alkene molecules so double bonds can be used for making polymers
  • helps manufacturers match supply with demand for products like petrol

Amount of fossil fuels being burnt is increasing because population are increasing:

• governments are concerned because of increasing carbon dioxide emissions
• countries such as India and China are using more fuel which adds to gas emissions
• governments are trying to cut carbon dioxide emissions but its a global problem

Combustion:

• Complete combustion: fuel burns in plenty of oxygen
  • fuel + oxygen --> carbon dioxide + water
  • more energy released

• Incomplete combustion: fuel burns in lack of oxygen
  • fuel + oxygen --> carbon monoxide / carbon(soot) + water

Clean air is made up of:

• 78% nitrogen, 21% oxygen, 0.035% of the remaining 1% is carbon dioxide
• % of carbon diozide has increased becuase of increasing population and deforestation

The carbon cycle:

• Plants take up carbon dioxide and produce oxygen in photosynthesis
• Plants and animals use up oxygen and produce carbon dioxide in respiration
• Animals and plants die eventually and get decomposed by decomposers, producing carbon dioxide
• Combustion of fuels uses up oxygen and produces carbon dioxide
• Marine animals convert carbon into limestone used to make shells which collect to form limestone
• Limestone weathers, producing carbon dioxide

The atmosphere:

• gases come from centre of Earth in a process called degassing
• atmosphere was originally rich in water vapour and carbon dioxide 
• water vapour condensed to form oceans and carbon dioxide dissolved in water
• percentage of nitrogen slowly increased and is unreactive so little was removed
• organisms that could photosynthesis evolved and converted carbon dioxide and water itno oxygen
• % of oxygen increased, % of carbon dioxide decreased until current levels reached

Pollution control:

• sulfur dioxide = a pollutant
  • dissolves in water to form acid rain which damages wildlife and limestone buildings 
• catalytic converter changes carbon monoxide into carbon dioxoide
  • nitric oxide reacts with carbon monoxide on the surface of catalyst to form natural components of air - nitrogen and carbon dioxide
  • 2CO + 2NO --> N2 + 2CO2

Hydrocarbons:

• consist of only hydrogen and carbon atoms
• alkanes = hydrocarbons that have single covalent bonds
  • formula = C_nH_2n+2
• alkenes = hydrocarbons that have a double covalent bond (involve two shared pair of electrons)
  • formula = C_nH_2n
• Bromine test for alkenes:
  • when bromine water is added to an alkene, it turns colourless (decolourises)
  • bromine and alkene form a di-bromo compound which is colourless
  • saturated = only single covalent bonds
  • unsaturated = at least one C=C bond

Alkanes: methane CH₄, ethane C₂H₆, propane C₃H₈, butane C₄H₁₀, pentane C₅H₁₂

Alkenes: ethene C₂H₄, propene C₃H₆, butene C₄H₈, pentene C₅H₁₀ 

Polymerisation:

• addition polymerisation = many alkene monomers react to give a polymer
  • needs high pressure and a catalyst
• displayed formula has a long chain, pattern repeating ecery two carbon atoms, two brackets and an 'n'

  ---> ethene monomer

  ---> polyethene polymer after ddition polymerisation

Gore-Tex:

• tough, lightweight, keeps UV light out 
• waterproof and breathable:
  • made from PTFE (polytetrafluoroethene) membrane
  • holes in PTFE are too small for water to pass through but big enough for water vapour to pass thorugh
• PTFE = too fragile so its laminated onto nylon to make a stronger fabric

Stretchy and rigid polymers: 

• plastics with weak intermolecular forces have low melting points and can be stretched easily because the molecules can slide over each other
• plastics with strong intermolecular forces or cross linking bridges have higher melting points, cannot be stretched easily and are rigid

Proteins in cooking:

• during cooking proteins permanently change shape - denatures
• texture of egg or meat changes when cooked because the shape of protein molecules change permanently
• potato is easier to digest when cooked because it is a carbohydrate:
  • starch grains swell up and spread out
  • cell walls rupture and lose their rigid structure and a softer texture is produced

Decomposition of sodium hydrogencarbonate:

• sodium hydrogencarbonate ---> sodium carbonate + carbon dioxide + water
• 2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O

Emusifiers:

• hydrophilic head bonds with water molecules
• hydrophobic tail bonds to oil molecules, keeping them together

Making esters for perfumes:

• alcohol + acid ---> ester + water
• made when acid added to alcohol and heated
• condenser stops gas form escaping and helps cool it down so reaction goes on for longer

Properties of perfumes:

• evaporate easily for particles to reach the nose
• non-toxic so it doesn't poison you
• not react with water so it doesn't react with perspiration
• not irritate the skin so it can be put directly on to skin
• be insoluble in water so it isn't washed off easily

The volatility (ease of evaporation) of perfumes:

• particles of liquid perfumes have weak forces of attraction so it's easy to overcome these attractions when they have enough kinetic energy

Water does not dissolve nail varnish:

• attraction between water molecules is stronger than the attraction between water and nail varnish molecules
• attraction between nail varnish molecules is stronger than the attraction between water and nail varnish molecules

Colloid: particles of paint are mixed and dispersed with particles of a binding medium

• this will not seperate because particles are scattered throughout the mixture and are small so they dont settle at the bottom

How emulsion (water based paints) paints dry:

• oil droplets in paint spread out and join and solvent evaporates
• oil forms a protective skin

How oil paints dry:

• solvent evaporates and oil is oxidised with atmospheric oxygen

Thermochromic pigments change colour at different temperatures.

Phosphoroscent pigments glow in dark because they absorb and store energy and release this energy when it is dark, they're safer than older alternative radioactive paints.