Lesson 2: RP: Chromotography

Question 1

What are the steps to the chromotography practical?

Answer 1

1.) Use a ruler to draw a horizontal pencil line on chromotography paper.
2.) Mark 5 pencil spots equally spaced out on the pencil line.
3.) Use a capilary tube to put a small spot of each of the known food colours and the unknown mixture (which contains the known colours) onto the pencil spots.
4.) Pour water into a beaker to a depth of 1cm.
5.) Attach the chromotography paper to a glass rod using tape and lower the paper into the beaker. Place a lid on the beaker.
6.) Allow the water and food colours to travel up the paper.
7.) Remove the paper from the water when the water has travelled 3/4 up the paper. Mark a point where the water reached (solvent front.)
8.) Hang the chromotography paper up to dry.

Question 2

What is a capilary tube?

Answer 2

• A capilary tube is a very thin glass tube.

Question 3

Why is it important to keep the spots of food colouring on the pencil line relatively small?

Answer 3

• This will prevent the colours from spreading into each other when they rise up the filter paper.

Question 4

Why must the sides of the chromotography paper not touch the sides of the beaker?

Answer 4

• As this would interfere with the way that water moves up the paper.

Question 5

Why do we place a lid on top of the beaker with the chromotography paper?

Answer 5

• This will reduce evaporation of the solvent ie. water.