Some examples from this set of practice questions
1.
Describe the biochemical test for starch
Answer: Iodine test (positive colour change of yellow-brown to blue-black)
2.
Describe the biochemical test for glucose
Answer: Use glucose testing strips (eg. Clinistix) and compare to a colour chart
3.
Describe the biochemical test for reducing sugars
Answer: Benedict’s test- add Benedict’s solution and heat gently (positive colour change of blue to green to yellow to orange to a brick red precipitate). Semi-quantitative
4.
Describe the biochemical test for non-reducing sugars
Answer: Firstly, non-reducing sugars test negative in the Benedict’s test. They must be hydrolysed with dilute hydrochloric acid, then neutralised with an alkali. They can then be tested again using the Benedict’s test
5.
Describe the biochemical test for protein
Answer: Biuret reagent (positive colour change of blue to purple)
6.
Describe how to prepare a chromatogram
Answer: Cut the chromatography paper to size. Draw the baseline in pencil. Use a micro-pipette to add the solutions to be tested (wait to dry and add another spot so that it’s concentrated). Place the lid on the container with the solvent so that the atmosphere becomes saturated.
7.
What precautions must be taken when drawing the baseline (line of origin)?
Answer: It must be drawn in pencil (as graphite is insoluble); it must be a few centimetre above the bottom of the chromatography paper.
8.
Name a precaution which must be taken when preparing a chromatogram
Answer: Only hold by the edges to prevent contamination
9.
Describe how to run a chromatogram
Answer: Suspend the chromatogram from the lid of the jar so that it is straight and is in contact with the solvent (but the solvent mustn’t reach the baseline). The solvent will run the length of the paper, but the chromatogram must be removed before the solvent reaches the top
10.
Describe how to develop a chromatogram
Answer: Mark the solvent front with pencil and allow to dry. The substances may be colourless, and they must be died. When dyed, the spots should be circled in pencil before it fades. Then, the chromatogram can be dried again.
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