We were given 5 solutions Essay
We were given 5 solutions labelled A, B, C, D and E. We were told that there was a reducing sugar, starch, non-reducing sugar, lipid and protein. My aim was to carry out some standard tests on these solutions and identify them as appropriate.MethodI will perform a standard test on each solution until they prove conclusive upon which I will move to the next solution. The tests are dteialed below and it is the order I followed on each solution.Background to Test 1: Reducing Sugar TestAll monosaccharides and some disaccharides are reducing sugars. The test for a reducing sugar is known as the Benedicts test. When a reducing sugar is heated with an alkaline solution of copper II sulphate it forms an insoluble precipitate of copper I oxide. The colour of the precipitate changes from green through yellow, orange and brown to deep red, depending on the quantity of reducing sugar present.Test 1* Put 1cm3 of test solution in test tube* Add 1 cm3 of Benedicts solution* Place in water bath for 5 minutes* Record any colour changeBackground to Test 2: Non-Reducing Sugar TestThere is no direct test for a non reducing sugar, but they can be identified by first hydrolising them with a dilute acid and then detecting the resulting reducing sugars by the Benedicts test. (This is why I have this test at number 2, so I automatically perform this after Test 1)Test 2* Follow as above and note that there was NO colour change* Add 1cm3 of HCL* Neutralise by adding a few drops of NaOH* Add 1cm3 of Benedicts solution* Heat in water bath* Record any colour changeBackground to Test 3: StarchStarch is easily detected by its ability to turn iodine in potassium iodide solution from a yellow colour to blue-black. The colouration is due to the iodine molecules becoming fixed in the centre of the helix of each starch molecule. It is important to do the test in room temperature as high temperature cause the starch helix to unwind which releases the iodine and assumes its usual yellow colouration.Test 3* Take a couple of drops of test solution and put in spotting tile* Add a few drops of iodine* Record any colour changeBackground to Test 4: LipidsThe test for lipids is known as the emulsion test. Ethanol reacts with the sample. To make sure the lipid dissolves in the sample it needs to be shaken. Water is then added. A cloudy white colour is the presence of a lipid. The cloudy colour is due to any lipid in the sample being finely dispersed in the water to form an emulsion. Light passing through this emulsion is refracted as it passes from oil droplets to water droplets, making it appear cloudy.Test 4* Put 1cm3 of test solution in test tube* Add a few drops of ethanol* Shake and water* Record any colour changeBackground to Test 5: ProteinsThe most reliable protein test is the Biuret test, which detects peptide links. First to a sample of the solution add an equal volume of sodium hydroxide. Secondly, add a few drops of very dilute (0.05%) copper II sulphate solution and mix gently. A purple colouration indicates the presence of peptide bonds and hence a protein.Test 5* Put 1cm3 of test solution in test tube* Add biuret solution* Record colour changeResults TableSolutionReducing SugarNon-Reducing SugarStarchLipidProteinAPurple XBBrown XCCloudy XDBlack XEBrown XConclusionI performed the tests as described in numerical order. If for example a test proved positive on Test 2, then I did not carry on with Test 3 and so on. My results are show above, it shows that solution A was a protein, solution B was a reducing sugar, solution C was a lipid, solution D was a starch and solution E was a non-reducing sugar.