Chemistry C1:

Overview of the topic C1 for Chemistry: OCR Gateway Science.

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Food additives:

  • Food additives are added for different reasons: 1) To preserve food from reacting with oxygen, bacteria or mould. 2) To give a different sensory experiencec such as to enhance the colour or flavour of the food.
  • Antioxidants stop food from reacting with oxygen. Ascorbic acid (vitamin C) is used in tinned fruits and winde as an antioxidant. Its E number is E300.

Food packaging: 

  • Intelligent or acrive packaging are methods used to stop food spoiling. They remove water or heat or cool the contents of the packs. Active packaging changed the conditions of the food to extend its shelf life. Intelligent packaging uses sensors to monitor the quality of the food and lets the customer know whent he food is no longer fresh.
  • Active packaging uses a polymer and a catalyst as a packaging film that scavenges for oxygen. It prevents the need for additives, such as antioxidants to be added to foods. It often involves the removal of water to make bacteria or mould more difficult to grow. Its used for cheese and fruit juice.
  • Intelligent packaging includes indicators on packages. An indicator on teh outside of a package shows how fresh a food is. A central circle darkens as the product loses its freshness.
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Emulsions and Emulsifiers:

  • Detergents are long molecules made up of two parts: a head and a tail. The tail is a 'fat-loving' part and the head is a 'water-loving' part.
  • Examples of emulsions are: Some paints, milk, which is an emulsion of oil in water and mayonnaise whihc is an emulsion of oil and vinegar with egg. Egg is the emulsifier. 
  • When mayonnaise is made, the egg yolk binds the oil and vinegar together to make a smooth substance.
  • The mayonnaise doesn't seperate as the egg yolk has a molecule that has two parts: 1) A water loving part that attracts vinegar to it, called the hydrophilic head. A water hating part that attracts oil to it is called the hydrophobic tail.
  • The hydrophobic tali is attracted into the lump of oil but the head isn't.
  • The hydrophilic head is attract to water and'pulls' the oil on the tail into the water.
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  • To make a perfume, alcohol is mixed with an acid to make an ester. alcohol + acid - ester + water.

Perfume properties:

A perfume needs to:

  • Evaporate easily so the perfume particles can reach the nose.
  • Be non-toxic so it doesn't poison people.
  • Be insoluble in water so it can't be washed off easily.
  • Not react with water so it doesn't react with perspiration.
  • Not irritate the skin so it can be sprayed directly onto the skin.


  • A solution is a solute and a solvent that don't seperate.

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  • If a liquid evaporates easily then the substance is volatile.
  • Particles in liquid perfume are weakly attracted to each other. When some of these particles increase their kinetic energy, the force of sttraction between them is overcome. The particles escape through the surface of liquid into teh surroundings as gsa particles. this is evaporation. The gas particles move through the air by diffusion to reach the sensors in the nose.
  • Water doesn't dissolve nail varnish. This is because the force of attraction between two water molecules is stronger than that between a water molecule and a molecule of nail varnish. Also, the force of attraction between two nail varnish molecules is stronger than between a nail varnish molecule and a water molecule. 
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Crude Oil:

Fossil fuels: 

  • Fossil fuels are finite resources because they are no longer being made. When these fossil fuels are used up, there will be no more. They're called a non-reneweable source.

Fractional distillation: 

  • Crude oil is a mixture of many types of oil, which are all hydrocarbons.
  • In fractional distillation, crude oil is heated at the bottom fo a tower. Oil that doesn't boil, sinks as a thick liquid to the bottom. This fraction is bitumen and is used to make tar for road surfaces. Bitumen has a very high boiling point. It 'exits' at the bottom of the tower.Other fractions boil and their gases rise up the tower. Fractions with lower boiling points, such as petrol and LPG, 'exit' at the top fo the tower where its colder.
  • Crude oil can be seperated because the molecules in different fractions have diffrent length chains. The intermolecular forces are different and are broken during boiling. The molecules of a liquid seperate from each other as molecules of gas. Heavy molecules such as bitumen have very long chains so the molecules have strong forces of attractions. Lighter molecules such as petrol have short chains. Each molecule has weak attractive forces and is easily sperated. Less energy is needed to pull them apart. They have very low boiling points.
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Craking is a process that turns large alkane molecules into smaller alkane and alkene molecules. It also makes useful alkene molecules witha  double bond, which can be used to make polymers. 

  • Alkanes have a general formula of: CnH2n+2.
  • Octane has 8 carbon atoms and 2n+2= 18 hydrogen atoms. The formula for octance is C8H18. 
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Making Polymers:


  • Polymerisation is the process in which many monomers react to give a polymer. This reaction requires high temperatures and a catalyst. 
  • You can recognise a polymer from its displayed formula by looking out for these features: A long chain, the pattern repeats every two Carbon atoms. There are two brackets on teh end with extended bonds through them. 
  • Addition polymerisation is the reaction of many monomers of the same type that have double bonds to form a polymer that has single bonds.
  • The displayed formula of an addition polymer can be constrcuted when the displayed formula of its monomer is give.
  • An unsaturated compound contains at least one double bond between carbon atoms.
  • A saturated compound contains only single bonds between carbon atoms.
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  • A hydrocarbon is a compound of carbon and hydrogen atoms only. An alkane has a single bond C-C. An alkene has one double bond C=C. 
  • Propane, C3H8 is a hydrocarbon and an alkane.
  • Propanol C3H7OH isn't a hydrocarbon because it contains an oxygen atom.
  • Propene is a hydrocarbon, an alkene and a monomer. Polypropene is the polymer.
  • Alkenes are unsaturated. The general formula of an alkene is cnH2n.
  • Alkanes are saturated. The general formula of an alkene is CnH2n+2. It has no double bonds.
  • Carbon and hydrogen atoms share an alectron pair to form covalent bonds.
  • Bromine solution is used to test for unsaturation. 
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Biodegradable and non-biodegradable polymers:

  • Scientists are veleoping addition polymers that are biodegradable. These are disposes of easily by dissolving. Biopol is a biodegradeable plastic that can be used to make laundry bags for hospitals. It dgreades when washed leaveing the laundry in the machine.
  • Disposable problems for non-biodegrabable polymers include the following: 1) Landfill sites get filled quickly and waste valuable land. 2) Buring waste plastics produces toxic gases. 3) Disposal by buring or landfill sites wastes a valuable resource. 

Stretchy polymers and rigid polymers: 

  • The atoms of the monomers in each of the chains in a polymer are held together by strong intramolecular bonds. The chains in the polymer are held together by weak intermolecular forces of attaraction. 
  • Plastics that have weak intermolecular forces of attraction have low melting points.
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Other plastics that form strong intermolecular chemical bonds or cross linking bridges between the polymer molecules have high melting points and can't be stretched easily as the molecules are rigid.

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  • A blue flame means that the fuel is burning in plenty of oxygen: complete combustion. 
  • A yellow flame means the fuel is burning in a shortage of oxygen: incomplete combustion.
  • The word equation for a fuel burning in air is: fuel + oxygen - carbon dioxide + water.
  • The reaction can be shown by using limewater to test for carbon dioxide.
  • Complete combustion is better because less soot is made and more heat energy is release. On top of this toxic carbon monoxide gas isn't produced.
  • The equation for complete combustion: CH4+O2 - CO2 + H20
  • The balanced equation for it is: CH4+2O2 - CO2 + 2H2O.
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