testing for carbohydrates 3.4

Question 1

what test is there for reducing sugars

Answer 1

Benedicts test for reducing sugars

Question 2

what are reducing sugars

Answer 2

sugars that reduce another molecule or chemical

Question 3

what solution is used in benedicts test for reducing sugars

Answer 3

Benedict’s reagent (an alkaline solution of copper(II) sulphate)

Question 4

explain the process of how to complete a benedicts test for reducing sugars

Answer 4

1)place the sample to be tested in a boiling tube, if it is not in liquid from, grind it up or blend it in water
2)Add an equal volume of Benedict’s reagent
3)Heat the mixture gently in a boiling water bath for 5 minutes

Question 5

• explain what the results of benedicts test for reducing sugars mean
• draw it

Answer 5

Question 6

explain the colour change in a positive benedicts test

Answer 6

• reducing sugars react with copper ions in Benedict’s reagent
• results in addition of electrons to blue Cu 2+ ions
  ^reduces them to brick red Cu atoms

Question 7

explain how benedicts reagent can be used to test for non-reducing sugars and why is this so

Answer 7

• boil the non-reducing sugar with dilute HCl (hydrolyses it to 2 reducing sugars) and so can be tested
• ^for using normal method

Question 8

what is the test for starch

Answer 8

the iodine test for starch

Question 9

explain the process to carry out a iodine test for starch

Answer 9

• add few drops of iodine to potassium iodide solution and mix with sample,
• if the solution changes colour from yellow/brown to purple/black starch is present in the sample

Question 10

what is the advantage of reagent strips

Answer 10

the advantage is that, with the use of a colour-coded chart, the concentration of the sugar can be determined

Question 11

what can be used to determine the concentration of reducing sugar

Answer 11

• colorimetry
• ^the more concentrated a solution is the more light it will absorb and the less light will be picked up by the sensory in the machine
• solutions are coloured after being tested for reducing sugars

Question 12

what are the steps to using a colorimeter to determine concentration

Answer 12

calibrate colourimeter using water
perfrom test on range of solutions of known conc and plot graph of results
recalibrate and test unknown solutinos and compare values to graph