(1) BIOCHEMICAL TESTS

Question 1

starch test (carbohydrates)

Answer 1

add iodine
positive = blue/black colour

Question 2

reducing sugar test (carbohydrates)

Answer 2

add benedicts reagent
heat
positive = from blue to green/yellow/orange/brick red (the more red the higher the concentration)

Question 3

non reducing sugar test (carbohydrates)

Answer 3

if reducing sugar test negative
add acid to hydrolyse and boil
add alkali to neutralise
add benedicts and heat
positive = same as benedicts

Question 4

what is a reducing sugar

Answer 4

reduce copper sulphate (blue colour) to copper oxide (red colour) in benedict’s
glucose, galactose, fructose, lactose, maltose

Question 5

what is a non-reducing sugar

Answer 5

reducing group involved in glycosidic bond, so cannot reduce copper sulphate to copper oxide
must hydrolyse first to break glycosidic bond, then can reduce
sucrose

Question 6

protein test

Answer 6

biuret reagent
positive = blue to purple

Question 7

lipid test

Answer 7

dissolve sample in ethanol
THEN add water
positive = white emulsion forms