Module 1, Chapter 1, PAGs

Question 1

describe the iodine test, and what it tests for

Answer 1

a test for the presence of starch

iodine is used (potassium iodide)
1) if the sample is not a liquid, grind it down and mix it with water, then filter out the larger bits
2) place a sample into a test tube
3) add a few drops of iodine and watch for a colour change

Question 2

describe the unmodified benedicts test, and what it tests for.

Answer 2

tests for the presence of reducing sugars. Take the food sample, and break it down using a pestle and mortar, the place it in a boiling tube and add the same volume of benedict’s. Heat it in a water bath, at 100 degrees for 5 minutes. Then analyse the colour changes.

Question 3

what is the staring colour and results for the benedicts test

Answer 3

starts a blue black colour
green - very low amount of sugar
yellow - low amount of sugar
brown - medium amount of sugar
brick red - large amount of sugar

Question 4

describe how the modified benedicts test can be used for non reducing sugars, give and example

Answer 4

1) first, use the benedicts test to test for reducing sugars, if there is a high number of these, the sample cannot be tested for non reducing sugars
2) if there is little or no colour change, add another sample of the unknown solution to a different test tube, and add some dilute HCl then heat for a few minutes
3) this with hydrolise the non reducing sugar into its monosaccharides (e.g sucrose - glucose + fructose) these reducing sugars will give a positive result
4) add sodium hydrogen carbonate to neutralise the acid, as benedicts reagent cannot work in acid solutions. (use universal indicator to test the alkilinity of the solution)
6) then add the benedicts reagent and leave the sample in a water bath
7) observe the colour change