core practical 1

Question 1

how are sugars classified as reducing or non-reducing

Answer 1

their ability to donate electrons ( reducing sugars that are able to donate electrons are oxidized

Question 2

what is the method for qualitative benedict’s test

Answer 2

1. add benedict reagent to a sample of the solution in a test tube
2. heat the test tube in a water bath
3. if a reducing sugar is present a colored precipitate will form
   - a positive test result will be the change in color:
   - blue ( no reducing sugar
   - green, yellow and orange ( low concentration of reducing sugar
   - brick-red ( high concentration of reducing sugar)

Question 3

what is the method for semi-qualitative benedict’s test

Answer 3

• set up standard solutions with known concentration of reducing sugar for serial dilution
• each solution is treated in the same way by adding the same volume of benedict reagent to each sample and heat in water bath for a set time to allow color change
• the same procedure is carried out on a sample with a unknown concentration of reducing sugar which is compared

Question 4

What is the method for qualitative iodine test

Answer 4

• add a few drops of orange/brown solution to a test sample
• if starch is present the colour will produce a blue-black colour

Question 5

What is the method of Semi-quantitative iodine test

Answer 5

• set up a standard solution of a known concentration by serial dilution
• add the same volume of iodine solution to all of the test tube and allow colour change for the same set of time
• the same procedure is carried out but the concentration of starch is known to compare
• to avoid human interpretaion a colourimeter is used
  The unknown sample can be determined using a calibration curve