Tests

Question 1

How do we test for proteins in a sample

Answer 1

Biuret test test for the presence of a peptide bonds
1. Add an equal volume of the same and biuret solution
2. Swirl the tube and look for the colour charge
3. If postive it will change from blue to purple if negative it will stay **blue **

Question 2

How do you test for lipids in a sample?

Answer 2

1. Crush material and mix with ethanol
2. Filter and remaining solid fron the ethanol solution
3. Carefully pour the ethanol into some water in a test tube - dont mix them
4. if postive it will form a milky white emulsion which forms on top of water but if negative it will stay clear

Question 3

How do you test for reducing sugars in a sample?

Answer 3

1. Add an excess volume of benedict’s reagent to a sample
2. Heat the mixture in electric water bath at 100 degrees for 5 mins
3. If postive results it will change from blue to green, orange or brick red precipitate forms depending on the concentration of sugar if not it will stay postive

Question 4

How to test for non reducing sugars in sample?

Answer 4

1. if the bendict’s reagent remains blue
2. Hydrolyse non- reducing sugars by adding 1cm3 of hcl and heat in a boiling tube in a water both for 5 mins
3. Neutralise the mixture using sodium carbonate solution
4. Procced withe benedicts test as usual

Question 5

How can the concentration of a solution be measure quantitatively?

Answer 5

• Use colourimetry to measure absorbance/% transmission. Interpolate a calibration curve from solutions of known concentration
• Use biosensors . A bioreceptor detects thte presence of a chemical . A transducer converts the reponse into detectable electrical signal

Question 5

How do you test for starch in a sample?

Answer 5

1. Add iodine soltion
2. if Postive result it will change from orange to blue-black

Question 6

Outline the principles and process of paper thin layer chromatography

Answer 6

1. use capillary tube to spot solution onto pencil ‘start line’ 1 cm above bottom of paper
   2.Place chromatography paper in solvent ( orgin should be above the solvent level)
   3.Allow solvent to run until it almost touches other end of the paper> molecules in mixture more different distances based on relative solubility in solvent/ attraction to paper

Question 7

What are Rf values?
How are they calculated?

Answer 7

• Ratios that allow comparision of how far molecules have moved in chromatograms
• Rf value - distance between orgin and centre of pigment spot/ distance between orgin and solvent front