tubes. The contents were shaken and allowed to settle. The
appearance of the liquids was examined and the observations were recorded.
Results:
Precautions: Three different test-tubes were used.
The results were left to settle
All observations were noted and recorded
3 different pipettes were used in method 3-one for each
liquid.
The Sudan dye was used carefully handled as it stains a lot.
Conclusion1: The oil dissolved completely in the ether and slightly in the
ethanol. However it did not dissolve in the distilled water.
Conclusion 2 : The solution containing both the ether and the oil turned
Completely red. The solution containing the ethanol and the oil turned faint red at the top but the red colour was darkest
at the bottom and the test-tube containing the water and the oil showed a red colour only on the top layer.
Conclusion 3: The ether did not make the brown paper translucent but the
Ethanol and the water gave a positive test for lipids ie they made it translucent.
Conclusion 4: The ether and the oil solution did not mix with the water added and instead formed two layers- the top one containing the oil ether and the dye and therefore a red solution and the bottom one was water. The test-tube containing the water, oil and the dye showed the same two layers it was showing previously ie a red colour on the top layer and water at the bottom but this time there was more water. The test-tube containing the ethanol, oil and dye showed a red colour on the top layer and a suspension in the bottom layer. Therefore one can conclude that the ether is not soluble in water, the oil is not soluble in the water and the ethanol is sparingly soluble in water.
Conclusion 5: The ether made no reaction with the liquid soap and two layers formed- the top one being the ether and oil solution and the bottom one being the soap together with the water added previously. The soap reacted with the oil in the second test-tube containing the oil, water and dye and the oil turned into tiny droplets which were suspended in the water. The soap also reacted with the oil which did not dissolve in the ethanol and this oil was also turned into droplets which fell to the bottom of the test-tube.
Discussion: Lipids are a varied group of molecules most of which are insoluble in water. Like carbohydrates, carbon, hydrogen, and oxygen are the principal elements of lipids although the oxygen content is much reduced. 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. Polar substances are those which contain slightly charged groups. The oil dissolved completely in the ether as this is also a non-polar substance and non-polar substances are able to dissolve in other non-polar substances. However the oil did not dissolve in the distilled water because as already explained above, water is a polar substance and therefore lipids can not dissolve in it. Therefore this explains why two layers formed in the test-tube. The upper layer was the oil wheras the lower layer was the water. Ethanol is a slightly polar substance and therefore the oil only dissolved slightly in it. However most of the lipid fell to the bottom of the test-tube.
Oil and water oil and ether
Explanation of method 2
Sudan dye is a hydrophobic substance and therefore dissolves in the oil and turns the parts containing oil red. Therefore it shows the position of the lipid more clearly. When the Sudan dye was added to the test-tube containing the oil and the ether the result obtained was a dark red solution. This was because the oil dissolved completely in the ether and so its particles were distributed throughout the liquid allowing the dye to react with them. The top layer turned red in the test-tube containing the water and oil as the oil rose to the surface since oil is less dense than water. Finally the test-tubes containing the ethanol and the oil showed a faint red colour at the top and this was because some of the oil dissolve in the alcohol but a dark red colour formed at the bottom as most of the lipid that did not dissolve fell to the bottom since ethanol is more dense than oil.
Explanation of method 3
This test is a test for lipids. Lipids turn the brown-paper translucent. When a drop of the liquid containing the ether, oil and Sudan dye was dropped onto the paper, it did not become translucent as no oil was present as it had already dissolved completely in the ether. When a drop of each of the other two solutions was added the brown paper did become translucent as the oil did not dissolve at all in the water and only dissolved slightly in the ethanol.
Explanation of method 4
This is the most reliable test for detecting the presence of a lipid. Since ether is a non-polar substance and therefore contains no slightly charged groups, it can not dissolve in water. Therefore this explains why the water added in this part of the experiment fell to the bottom of the test-tube forming two layers-the top one being the oil dissolved in the ether together with the Sudan dye. The water added just fell to the bottom also, in the second test-tube containing the water and the oil, joining the previously added distilled water. Ethanol is slightly polar and therefore is able to react with water slightly and dissolve in it. When the water was added to the third test-tube some of the ethanol reacted with the water and dissolved in it forming a suspension where as the layer containing the oil which did not dissolve in the ethanol previously, together with the Sudan dye rose to the surface. This explains why two layers were observed- the top one being red ( because of the Sudan dye ) and the bottom one being a suspension of the ethanol dissolved in the water with a few lipid particles coming from the oil which dissolved in the alcohol, floating around in the solution.
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.
References:
http://jschenk.chem.wsu/chem102/102.lipfatsoap.html
Roberta Scalpello Science 1 A
