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Test the hypothesis that lipids have special properties inrelation to solvents.

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Lipids Aim: To test the hypothesis that lipids have special properties in relation to solvents. Requirements: Distilled water Ethanol Ether Sudan Dye Oil Pieces of brown paper Liquid soap Preparation: 3 different test-tubes were prepared. One contained 5ml of distilled water, the second one contained 5ml of ether and the third one Method 1: 10 drops of oil were added to each of the three test-tubes containing the liquids and the contents were shaken thoroughly. The contents were then left to settle and later were examined. Any observations made were recorded. Method 2: A few grains of Sudan dye were added to each of these test-tubes and the contents were shaken once again. They were then left to settle and after a few minutes the test-tubes were examined and any observations made were recorded. Method 3: A drop of liquid from each test-tube was transferred onto a piece of brown paper using a pipette. The brown paper was left to dry. The results were examined and any observations were recorded, Method 4: After half the contents of each test-tube were poured into 3 different clean test-tubes, an equal amount of distilled water was added to the first set of tubes. The test-tubes were then shaken thoroughly. The appearance of each test-tube was examined and any observations made were recorded. Method 5: 2 drops of liquid soap were added to the second set of test- tubes. ...read more.


Fats, phospholipids, steroids, carotenoids, and waxes are lipids. Fats are the most abundant group of lipids in the biological world. Fats are composed of three fatty acid molecules bonded to a molecule of the alcohol glycerol. Fats have at least twice the energy ,storing capacity per unit weight as carbohydrates do. Cholesterol is an important steroid that is a part of some hormones. Steroids differ from most other lipids by virtue of the structure of steroids consisting of carbon rings instead of chains. A typical fat made up of three fat acids and glycerol One of the biological important characteristics of fats, and lipids in general, is their insolubility in water. Lipids are made of long chains of hydrocarbons with relatively little oxygen . As a result of this they tend to be non-polar and do not dissolve into polar solvents such as water. Another group of important lipids are the phospholipids. Phospholipids differ from fats in only having two fatty acid chains and a polar head rather than a glycerol head. The insolubility in water (hydrophobic) of the fatty acid tails and the solubility of the polar head (hydrophilic) is important in the functioning of the phospholipid membrane of cells. Explanation of Method 1: Since lipids are made up of long chains of hydrocarbons with relatively little oxygen they are said to be hydrophobic as they dont dissolve in polar substances such as water. ...read more.


Explanation of method 5 Soaps (and detergents) work because their structures combine in one molecule a hydrocarbon chain which is hydrophobic (rejects water) and lipophilic (attracts oily materials) with an end which is hydrophilic (attracts water) and lipophobic (rejects oily materials). The long "fatty" chains provide solubility in hydrocarbons (grease) and the polar, usually ionic, heads provide solubility in water. If both oily and watery materials are present, a soap provides a "bridge" by dissolving its hydrocarbon chain in a droplet of oil in such a way that the ionic, hydrophilic, end sticks out into the surrounding water. This arrangement is called a micelle and permit soapy water to "wash away" greasy materials. This means that the soap emulsified the oil in the test-tube containing the water, oil and Sudan dye.This means that the soap broke down the oil into tiny fat droplets which remained suspended in the water. The soap also emulsified the oil found at the bottom of the test-tube containing the ethanol, oil, water and Sudan dye. However there was no reaction observed in the test-tube containing the ether, oil, water and Sudan dye as the oil had already completely dissolved in the ether. The soap did however react with the water and this explains the result obtained of two layers- the oil dissolved in the ether together with the Sudan dye on the top and the soap and water at the bottom. ...read more.

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