PAG 9 - qualitative testing-methods

Question 1

aim

Answer 1

test qualitatively for presence of glucose (reducing sugar) & sucrose (non-reducing sugar)

Question 2

how many methods 2 & what are they

Answer 2

2
method 1 = testing for reducing sugar
method 2 = testing for non-reducing sugar

Question 3

method 1: reducing sugar

Answer 3

1. label 4 boiling tubes A-D & place 4cm3 of corresponding sample in each (fresh syringes)
2. use dropping pipette to add ~2cm3 benedict’s reagent to each
3. record observations immediately after adding benedict’s
4. place boiling tubes in water bath
5. after 2 min, record observations & replace in water bath
6. after 2 more min, remove tubes & record final observations & conclusions on presence/absence of reducing sugar

Question 4

method 2: non-reducing sugar

Answer 4

• do non-reducing sugar test first !!!

1. put 4cm3 of samples A-D in labelled boiling tube (fresh syringe)
2. use dropping pipette & add ~2cm3 of 2 mol dm3 HCL to each
3. place into water bath & incubate for 2 min
4. remove from water bath & allow to cool
5. neutralise acid by gradually adding sodium hydrogen carbonate until no more effervescence observed
6. check pH with indicator paper - if lower than 7, repeat step 5
7. use dropping pipette to add ~2cm3 benedict’s reagent
8. record observations immediately
9. place all into water bath
10. after 2 min, record observations & replace in water bath
11. after further 2 min, remove from water bath & record final observations/make conc. about presence/absence of non-reducing sugar

Question 5

extension q. - what improvements can you suggest to the method you were given for this qualitative test

Question 6

extension q. - what changes would you make to obtain semi-quantitative results

Question 7

extension q. - outline a method for fully quantitative test for reducing sugars

Question 8

extension q. - suggest how you could distinguish a sample of glucose from a sample of maltose using benedict’s reagent