Tests

Question 1

Starch

Answer 1

Iodine solution

+ve then yellow/ brown ——> black-blue

Iodine forms trioxide ion , which slips into middle of amylose helix

Question 2

Reducing sugars

Answer 2

Benedicts solution

Blue — green — yellow — orange — red

Benedicts contains cu2+ ions — reduced to cu+ forming red cu2o

Question 3

Non reducing sugars

Answer 3

Hydrolyse bonds —- free reducing grps , test for reducing sugars

• test sample 4 reducing sugars
• boil sample w hydrochloric acid — hydrolyse sucrose
• cool solution , neutralise w hydrogen carbonate
• rest for reducing sugars again

Ppt formed ( same as reducing)

Question 4

Tests for lipids

Answer 4

Emulation test
- mix sample w ethanol 
- filter
- pour solution in clean test tube 
\+ cloudy white emulation formed

Question 5

Test for proteins

Answer 5

Bitter test
+ light blue — lilac

• formed by complex between n in peptide chain and cu 2+ ions
• test for presence of peptide bonds