Practical- Starch Test

Question 1

What are the Materials needed for the test?

Answer 1

Eye protection

Beaker for boiling water, 250 cm3

Forceps, 1

Boiling tube, -1

Petri dish

Ethanol -10ml

Iodine solution

Leaf

Dropper

Glassrod

White tile

Question 2

What are the steps for the test?

Answer 2

a Put on your eye protection.

b At your desk, boil 250ml water into a large beaker.

c Using forceps, pick up one of your leaves and hold it in the hot water for about one minute.

d Using forceps, remove the leaf from the boiling water and note how it has changed.

e Drop the leaf into a boiling tube and push it to the bottom with a glass rod.

g Add enough ethanol to cover the leaf, and place the boiling tube in your beaker of hot water, or in the hot water bath.

h Watch as the ethanol boils and the green colouring (chlorophyll) is removed from the leaf. This will take a few minutes.

j Using forceps, remove the leaf from the boiling tube and rinse the leaf in cold water.

k Put the leaf in a Petri dish.

l Add iodine solution to the leaf from the dropper bottle. Make sure the leaf is completely covered with iodine.

m Watch for a few minutes to see if a blue-black colour develops in any part of the leaf. A blue-black colour with iodine solution indicates that starch is present.

n Wash your hands to remove any traces of plant sap, or the chemicals that you have used.

Question 3

What colour is the leaf before boiling? Why is it that colour?

Answer 3

The green pigment chlorophyll is present in the leaf, which is why it is green.

Question 4

Why do we boil the leaf?

Answer 4

To soften the cuticle and disrupt the cell membrane so iodine can penetrate through the leaf.

Question 5

Why do we boil the leaf in ethanol? What happens to the leaf once we boil it?

Answer 5

To extract chlorophyll from the leaf? Since chlorophyll is soluble in ethanol, it dissolves in the ethanol, turning it green.

Question 6

What happens to the leaf once it has been taken out of ethanol?

Answer 6

Once the chlorophyll is extracted from the leaf it turns light green or translucent.

Question 7

What happens to leaf once you soak it iodine?

Answer 7

The starch and iodine solution react to form a blue-black compound?

Question 8

State 3 hazards-risks-precautions

Answer 8

Bunsen burner-it could burn us or the paper-keep a safe distance away while handling it and keep flammable objects away

Iodine Solution-irritate our eyes-wear protective goggles

Ethanol- Flammable- Turn of bunsen burner while using it.