Paper Chromatography

Question 1

Write a method.

Answer 1

1. Use a ruler to draw a horizontal pencil line 2 cm from the bottom short edge of the chromatography paper. This is your origin line.
2. Mark five pencil spots at equal intervals across the origin line. Make sure you keep at least
3. 0.5 cm away from each edge of the paper.
4. Use a glass capillary tube to put a small spot of each colouring A, B, C and D on four of the pencil spots. Use a different tube for each colouring. Use the fifth tube to put a small spot of
   the unknown mixture U on the fifth pencil spot. Try to make sure each spot is no more than 2-3 mm indiameter.
   Label each spot in pencil.
5. Pour water into the beaker to a depth of no more than 1 cm.
6. Clip the top short edge of the chromatography paper to the wooden spill. The top end is the end furthest from the spots.
7. Carefully rest the wooden spill on the top edge of the beaker. The bottom edge of the paper should dip into the water solvent. Wait for the water solvent to travel at least three quarters of the way up the paper. Do not
   disturb the beaker during this time.
8. Carefully remove the paper from the beaker. Draw another pencil line on the dry part of the paper as close to the wet edge as possible. This is called the solvent front line.
9. Hang the paper up to dry thoroughly.
10. Measure the distance in mm between the two pencil lines. This is the distance travelled by the water solvent.
11. For each of food colour A, B, C and D measure the distance in mm from the start line to the middle of each spot

Question 2

How do you find the Rf?

Answer 2

Distance travelled by the sample/distance travelled by the solvent

Question 3

Why is chromatography classed as a physical process?

Answer 3

It is physical substances moving due to another physical property

Question 4

What is the stationary and mobile phase?

Answer 4

Stationary= the paper
Mobile= the solvent

Question 5

Why is pencil used to draw the lines?

Answer 5

The pencil will not separate due to the mobile phase

Question 6

Why should the water be below the pencil line?

Answer 6

So the water (solvent) is able to move through the paper into the ink