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 change
Background to Test 2: Non-Reducing Sugar Test
There 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 change
Background to Test 3: Starch
Starch 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 change
Background to Test 4: Lipids
The 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 change
Background to Test 5: Proteins
The 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 change
Results Table
Conclusion
I 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.
