Biology practical = Qualitative tests

Question 1

Test for starch

Answer 1

Add drops of iodine to sample

Question 2

Positive test for starch

Answer 2

Colour change from orange to black

Question 3

Test for reducing sugars

Answer 3

Add Benedict’s solution to sample
Heat in boiling water bath

Question 4

Positive result for reducing sugars

Answer 4

Colour change from blue solution to green, yellow, orange or red precipitate dependent on conc of sugar solution

Question 5

Test for non reducing sugar

Answer 5

Following negative Benedict’s test: acid hydrolysis to break glycosidic bonds in the disaccharide:
Add HCl and put in boiling water bath
Cool solution and add sodium hydroxide to neutralise
Complete Benedict’s test: place in another boiling water bath

Question 6

Positive result for Benedict’s solution

Answer 6

After acid hydrolysis and Benedict’s solution, the blue solution changed to yellow/green/red/orange precipitate

Question 7

Test for proteins

Answer 7

Add biuret solution

Question 8

Positive result for biurets test

Answer 8

Colour change blue to purple

Question 9

Test for lipids

Answer 9

Dissolve in ethanol
Add distilled water and mix

Question 10

Positive result for lipids test

Answer 10

A white emulsion will form