Required Practical 7: Chromotagraphy

Question 1

What is the equipment list for RP7?

Answer 1

• Filter paper
• Leaf sample
• Pestle and Mortar
• Pencil
• Ruler
• Capillary Tube
• Chromatography solvent
• Acetone

Question 2

What is the method for required practical 7?

Answer 2

1. Draw a straight line in pencil 1cm above bottom of filter paper.
2. Place leaf in mortar. Add acetone and use pestle to grind up leaf to release pigments.
3. Use capillary tube to extract some pigment and blot on centre of pencil line drawn.
4. Suspend paper in solvent so the liquid isn’t above pencil line. Leave paper until the solvent has run up paper to near the top.
5. Remove paper from solvent ad draw a pencil line, marking the solvent front.
6. Calculate RF value for each spot.

Question 3

Why is pencil used to mark the line?

Answer 3

The ink and pigments would mix.

Question 4

Why should you measure to the centre of the pigment spot?

Answer 4

• It would standardise the readings.
• It allows comparisons to be made.

Question 5

Why can’t you move the bottle once the filter paper is in it?

Answer 5

• Pigments could wash off paper.
• Solvent would run off side of paper.

Question 6

List some practical precautions.

Answer 6

• No flames near solvent.
• Use a fume cupboard.
  Don’t let paper touch the sides of the jar.
• Solvent should start below pencil line.
• Stop before solvent reaches top of the paper.

Question 7

Give the risk and safety precautions for acetone usage.

Answer 7

Risk: Flammable, irritation to eyes, inhalation may lead to dizziness.
Safety precaution: Eye protection, room is well ventilated, keep away from naked flame.

Question 8

RF value calculation

Answer 8

RF value= distance moves by pigment/ distance moved by solvent front

RF value is less than 1.