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VEGETABLE OILS A guide for GCSE students 2010 KNOCKHARDY PUBLISHING SPECIFICATIONS VEGETABLE OILS INTRODUCTION This Powerpoint show is one of several produced to help students understand selected GCSE Chemistry topics. It is based on the requirements of the AQA specification but is suitable for other examination boards. Individual students may use the material at home for revision purposes and it can also prove useful for classroom teaching with an interactive white board. Accompanying notes on this, and the full range of AS and A2 Chemistry topics, are available from the KNOCKHARDY SCIENCE WEBSITE at... www.knockhardy.org.uk/gcse.htm All diagrams, photographs and animations in this Powerpoint are original and created by Jonathan Hopton. Permission must be obtained for their use in any commercial work. ANIMAL, VEGETABLE OR MINERAL? We obtain oil from a variety of natural resources… ANIMAL OILS COD LIVER, BUTTER MINERAL OILS LUBRICATING OIL VEGETABLE OILS RAPE SEED, OLIVE, SUNFLOWER ANIMAL, VEGETABLE OR MINERAL? We obtain oil from a variety of natural resources… ANIMAL OILS COD LIVER, BUTTER MINERAL OILS LUBRICATING OIL VEGETABLE OILS RAPE SEED, OLIVE, SUNFLOWER The source of the these substances involves PHOTOSYNTHESIS and energy from the SUN. 6CO2 + 6H2O C6H12O6 + 6O2 The glucose produced is then converted to a variety of different chemicals within the organism. EXTRACTING VEGETABLE OILS Options… HARVEST SEEDS CRUSH SEEDS PLANT SEEDS EXTRACT OIL EXTRACTING VEGETABLE OILS Options… HARVEST SEEDS CRUSH SEEDS PLANT SEEDS EXTRACT OIL Options… HARVEST PLANTS PLANT SEEDS HEAT IN STEAM DISTILL OFF OIL STRUCTURE OF VEGETABLE OILS Each vegetable oil has a slightly different structure. The molecules have much in common because they contain chains of carbon atoms. –H–H–H–H–H–H –C–C–C–C–C–C– –H–H–H–H–H–H STRUCTURE OF VEGETABLE OILS Each vegetable oil has a slightly different structure. The molecules have much in common because they contain chains of carbon atoms. In some oils, there are carbon atoms joined by double carbon-carbon bonds. These are UNSATURATED OILS. They can be detected using bromine solution. –H–H–H–H–H–H –C–C–C–C–C–C– –H–H–H–H–H–H –H–H–H–H–H–H –C–C=C–C–C–C– –H–H–H–H–H–H STRUCTURE OF VEGETABLE OILS Each vegetable oil has a slightly different structure. The molecules have much in common because they contain chains of carbon atoms. STRUCTURE OF VEGETABLE OILS Each vegetable oil has a slightly different structure. The molecules have much in common because they contain chains of carbon atoms. Some oils are SATURATED All the carbon-carbon bonds are SINGLE STRUCTURE OF VEGETABLE OILS Each vegetable oil has a slightly different structure. The molecules have much in common because they contain chains of carbon atoms. Some oils are SATURATED All the carbon-carbon bonds are SINGLE Others are UNSATURATED A DOUBLE carbon-carbon bond appears in the structure SATURATED OR UNSATURATED? ADD BROMINE SOLUTION; if the reddish-brown colour is removed the substance is UNSATURATED. A PLACE A SOLUTION OF BROMINE IN A TEST TUBE B ADD THE OIL TO BE TESTED AND SHAKE C IF THE BROWN COLOUR DISAPPEARS THEN THE OIL IS UNSATURATED. A B C PROPERTIES OF VEGETABLE OILS - Experiment Add some bromine solution [CARE] to a test tube followed by a small amount of the oil/fat. Place a bung in the test tube and shake to ensure mixing. If the reddish-brown colour is removed the substance is UNSATURATED. FAT / OIL BUTTER DRIPPING LARD MARGARINE OLIVE OIL SUNFLOWER OIL Appearance at Room Temp Reaction with bromine water Saturated or Unsaturated ? EMULSIONS Emulsions are mixtures of oil and water. Examples include… MILK, MAYONNAISE, ICE CREAM Droplets of oil in water EMULSIONS Emulsions are mixtures of oil and water. Examples include… MILK, MAYONNAISE, ICE CREAM Emulsions often differ significantly from the substances that make them up. For example, oil and water are both runny but mayonnaise has a slightly stiffer quality. Droplets of oil in water EMULSIONS Emulsions are mixtures of oil and water. Examples include… MILK, MAYONNAISE, ICE CREAM Emulsions often differ significantly from the substances that make them up. For example, oil and water are both runny but mayonnaise has a slightly stiffer quality. Emulsions are often found in food. This is because they produce a smoothness that is pleasant in the mouth. Droplets of oil in water EMULSIFIERS Emulsifiers make sure that the oil and water molecules stay together and do not separate. This is most important in sauces so that they stay creamy and don’t go lumpy. WATER OIL How an emulsifier works EMULSIFIERS Emulsifiers make sure that the oil and water molecules stay together and do not separate. This is most important in sauces so that they stay creamy and don’t go lumpy. WATER OIL Emulsifiers have a special structure; one end is attracted to water and the other is attracted to the oil. attracted to water attracted to oil In some ways, they are like soap. How an emulsifier works STRUCTURE OF VEGETABLE OILS Each vegetable oil has a slightly different structure. The molecules have much in common because they contain chains of carbon atoms. STRUCTURE OF VEGETABLE OILS Each vegetable oil has a slightly different structure. The molecules have much in common because they contain chains of carbon atoms. WHY COOK WITH OIL? Cooking oils have a higher boiling point than water so can be heated to a higher temperature in a pan. This affects how we cook food. Potatoes cooked (fried) in oil are much crisper than if cooked (boiled) in water. WHY COOK WITH OIL? Cooking oils have a higher boiling point than water so can be heated to a higher temperature in a pan. This affects how we cook food. Potatoes cooked (fried) in oil are much crisper than if cooked (boiled) in water. The boiling point of a substance depends on the size of the attractive forces between the molecules. The bigger the molecules, the larger the attractive forces. has a higher boiling point than WHY COOK WITH OIL? Unsaturated oils are usually liquids at room temperature. This is because the carbon-carbon double bonds in their structure affect the shape of the molecules preventing them fitting closely together. This reduces the forces of attraction between the molecules. WHY COOK WITH OIL? If the carbon-carbon double bond is converted to a single bond, the overall shape of molecules is changed and they fit together better and can get closer. This increases the forces of attraction and raises the boiling point and melting point of the oil. All the C=C bonds have been converted to C-C bonds. With the higher melting point, the oil becomes a solid at room temperature. This process is known as HARDENING. HARDENING OILS How is it done? To harden an oil you must CONVERT THE C=C BONDS TO C-C BONDS. This is done by bubbling hydrogen gas (H2) through oil heated to 60°C. Finely divided nickel is added to the oil. The nickel acts as a CATALYST. Catalysts speed up chemical reactions but remain chemically unchanged and are not used up. Nickel 60°C USES OF OILS, FATS AND EMULSIFIERS BUTTER USES OF OILS, FATS AND EMULSIFIERS SPREAD USES OF OILS, FATS AND EMULSIFIERS CHEESECAKE USES OF OILS, FATS AND EMULSIFIERS CHOC ICE USES OF OILS, FATS AND EMULSIFIERS CHOCOLATE ICE CREAM USES OF OILS, FATS AND EMULSIFIERS HORSERADISH SAUCE USES OF OILS, FATS AND EMULSIFIERS COLESLAW AQA C1.6 Vegetable oils - summary Some fruits, seeds and nuts are rich in oils that can be extracted. The plant material is crushed and the oil removed by pressing or in some cases by distillation. Water and other impurities are removed. Vegetable oils are important foods and fuels as they provide energy and nutrients. Vegetable oils have higher boiling points than water and so can be used to cook foods at higher temperatures than by boiling. This produces quicker cooking and different flavours but increases the energy that the food releases when it is eaten. Oils do not dissolve in water. They can be used to produce emulsions. Emulsions are thicker than oil or water and have many uses that depend on their special properties. They provide better texture, coating ability and appearance, for example in salad dressings, ice creams, cosmetics and paints. Emulsifiers have hydrophilic and hydrophobic properties. Vegetable oils that are unsaturated contain double carbon–carbon bonds. These can be detected by reacting with bromine water. Vegetable oils that are unsaturated can be hardened by reacting them with hydrogen in the presence of a nickel catalyst at about 60°C. Hydrogen adds to the carbon–carbon double bonds. The hydrogenated oils have higher melting points so they are solids at room temperature, making them useful as spreads and in cakes and pastries. VEGETABLE OILS THE END © 2011 JONATHAN HOPTON & KNOCKHARDY PUBLISHING