Wednesday, 21 November 2012

Chemistry AQA GCSE Core Revision Notes on Extracting Vegetable Oils




Extracting vegetable oils

  • The plant materials are crushed and pressed to squeeze the oil out. Olive oil is obtained this way.
  •  Sometimes the oil is more difficult to extract and has to be dissolved in a solvent.
  • Once the oil is dissolved, the solvent is removed by distillation, and impurities such as water are also removed, to leave pure vegetable oil. Sunflower oil is obtained in this way.
Vegetable oils in food:
  • All vegetable oils have molecules that have chains of carbon atoms with hydrogen atoms attached.
  • In some vegetable oils there are carbon-carbon double bonds which are known as unsaturated oils
  • We can use the same test as we use for testing alkenes for testing unsaturated oils.
Using plant oils:
  • Biodiesel is a fuel made from plant oils and can be used in any and car or van that has a diesel engine.
  • It is made from oils that come from plants. Plants use photosynthesis to convert solar energy to chemical energy. The chemical energy is released when the biodiesel is burned.
Advantages:
  • It is renewable, biodegradable and non- toxic.
  • Doesn’t give off as many poisonous gases.
  • It is carbon neutral (the amount of carbon dioxide it gives off is balanced by the amount it absorbs).

Making Alcohol:

Alcohol is a very useful substance:
  • It makes an excellent solvent
  • Can be used as an alternative fuel
  • Can be made into an alcohol beverage or posh vinegar.

Methods of making it:
1) Fermentation:
  • Yeast is mixed with sugar and kept warm for a period of time.
  • The yeast uses the sugar for respiration producing Ethanol and Carbon Dioxide

                     Yeast + warm ≈ 45°C
C6H12O6                                            2C2H5OH + 2CO2

2) Reaction of ethene and steam:
  • Ethene is mixed with steam and passed over a at catalyst at very high temperatures.

C2H4  +  H2O                  C2H5OH
Ethene    steam                   ethanol

Text Box: Reaction of ethene and steam:
Advantages:
• Continuous process
• Fast
Disadvantages:
• Non renewable 
• Product is impure
Fermentation:
Advantages:
  • Renewable
  • Very pure product
Disadvantages:
  • Batch process
  • Slow
  • Lots of energy to purify

Emulsions:
·         It is a combination of two liquids that do not normally mix.
·         It works if tiny droplets of one liquid spread out throughout the other liquid.
Eg. Milk is made from tiny droplets of animal fat dispersed in water.

Emulsifiers:
  • They stop the two liquids separating out into two layers.
Eg: Egg yolks are a very good emulsifier. Normally oil and water don’t mix but if you add egg yolks then it stops them separating.

Saturated and Unsaturated Fats:
  • Fats are long chain molecules they store lots of energy so we should be careful of how much we eat.
Sources of fat:
Saturated: Animal based products, ie. Meats, cheese, eggs, milk, lad, butter
Unsaturated: Vegetable fats, ie. Beans, pulses, nut, seeds, avocados, olives, margarine.

Making Margarine:
Margarine is lower in saturated fat and therefore is a healthier option.
  • Seeds are washed and crushed
  • A solvent is added
  • The solvent is removed and bacteria killed using steam
  • Hydrogen gas is bubbled through at 60 °C and a catalyst of nickel is added
  • During hydrogenation the liquid changes to a solid
  • The margarine is packaged and sold

Link between Fat and Cholesterol:
  • Cholesterol and fat travel in the bloodstream in packages called ‘Lipoproteins’
  • One is Low-Density Lipoproteins (LDL) which is considered ‘bad’ because it increases the risk of fatty deposits forming in the arteries.
  • The other is High-Density Lipoproteins (HDL) which has a protective effect against heart disease.
  • To protect against heart disease it is important to lower LDL but NOT HDL. Therefore it is important to eat unsaturated fats because they lower LDL but not HDL.


Additives:
·         These are put in foods to improve taste appearance and to preserve it for longer.
·         Additives that have been approved for use in Europe are called E-Numbers,
  • There are 6 groups of food additives and each group is given an E-Number and the first digit tells us what type of additive it is.
  • E1… = colours, E2… = preservatives, E3… = antioxidants, E4… =emulsifiers, stabilisers and emulsions, E5… = acidity regulators, E6… = flavourings.

Chromatography:
·       This technique separates different compounds based on how well they dissolve in a particular solvent. Their solubility then determines how far they move up the chromatography paper.
·        Each component of the dye spreads out at different rates so you can tell what makes up the dye.
·       You can than compare them to known substances or using a mass spectrometer.
·       Rf Value = distance moved by coloured spot
                        distance moved by solvent           

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