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Chemistry - Vegetable Oils and Their Uses (AQA Syllabus A)

In GCSE Science students will look at crude oil and other fuels but they will also look at plant oils. This quiz is all about vegetable oils and their different uses, such as food, fuel and other products.

Many plants produce useful oils that have many uses. They can be converted into various things including processed foods like margarine, fuels like biodiesel, cosmetics and cleaning products. The oils themselves are frequently used in emulsions like salad dressings. But one of the main uses of vegetable oils is in cooking. They have much higher boiling points than water and so can be used to cook foods at higher temperatures than by boiling. Food can therefore be cooked faster than it would have been by cooking in water and different flavours are developed. The drawback to this is that it increases the energy that the food releases when it is eaten so eating too many foods that have been fried or deep fried can have negative consequences for your health.

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One of the ways in which your knowledge of vegetable oils could be tested is that you are asked to evaluate given data about an oil that you have probably never heard of. In such cases, keep calm and think about what you do know, then look how it can be applied to the questions. For example, that type of question could test your knowledge of the economic, ethical and environmental issues surrounding the use of vegetable oils as fuels or why certain fats and oils are used in cakes and pastries!

Some, but not all, fruits, seeds and nuts are rich in oils that can be extracted. To obtain the pure plant oil, the fruit, seeds or nuts are crushed and the oil is removed by pressing. In some cases, it is obtained by distillation, for example corn oils and soyabean oils. The seeds are crushed and the oil is extracted by using a solvent to dissolve it from the mixture. The solvent/oil mixture is then distilled to obtain the oil. Water and other impurities are removed during processing.

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  1. Unsaturated oils usually take what form at room temperature?
    Saturated oils tend to be more solid than equivalent unsaturated oils, which are usually liquids at room temperature
  2. Why is eating a diet mainly of food cooked in vegetable oils unhealthy?
    Vegetable oils are high in calories so it is easy to put on weight if you don't exercise a lot more
  3. Why do foods cooked in vegetable oils usually contain more energy than foods cooked by other methods?
    During cooking using vegetable oils, some of the oil replaces water in the cells of the food as well as remaining on the surface. Water has zero food energy value but cooking oils have high energy contents
  4. Oils and fats can be termed saturated or unsaturated. Unsaturated means what?
    As with the alkenes, unsaturated oils and fats will decolourise bromine water
  5. Why does food cook faster in vegetable oils than in boiling water?
    Kinetic theory meets cooking! Cooking is simply a way of making chemical changes in food to alter taste and texture. Chemical reactions go faster at higher temperatures
  6. What chemical is needed to turn vegetable oil into margarine?
    The process is called hydrogenation and is carried out at a high temperature (600oC) using a catalyst (nickel)
  7. What is an emulsion?
    When an oil and water are mixed together, tiny droplets of one liquid spread through the other. In time, an emulsion will separate - the water and oil do not mix permanently and end up as layers
  8. What are the two methods of extracting vegetable oils?
    Pressing is usually used to extract the more 'traditional' oils like olive oil
  9. An emulsifier must be added to make an emulsion (such as paint, skin cream or mayonnaise) stable. Which of the following are the characteristics of a good emulsifier?
    The molecules that make good emulsifiers have one end that bonds with water (hydrophilic) and the other end bonds with oils and fats (hydrophobic). Lecithin is a natural emulsifier commonly used in foods
  10. Which parts of a plant are usually used as the source of vegetable oils?
    Oils can be extracted from flowers but these yield much smaller amounts and often more aromatic oils

Author: Kev Woodward

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