4.6.5 - chromotography

Question 1

what is chromatography

Answer 1

a method of separating mixtures - usually mixtures of dyes in inks, paint, food colouring, etc.

Question 2

chromatography method

Answer 2

1) draw a line near the bottom of the chromatography paper in pencil - (pencil is insoluble so will not dissolve in the solvent)

2) add spots of different dyes to the line at different intervals

3) place the paper in a beaker of solvent - (make sure solvent is below pencil line - otherwise the inks will dissolve into the solvent)

4) place a lid on the beaker - (to stop the solvent evaporating)

5) allow the solvent to move up the paper until it is just below the top

6) take the paper out and mark on where the solvent has reached - (this is called the solvent font)

7) allow the paper to dry

Question 3

how does chromatography work

Answer 3

the dyes move up the paper at different rates:
- the more soluble the dye in the solvent - the further up the paper it will go
- if the dye is insoluble, it will not move from the baseline

Question 4

how to interpret a chromatogram

Answer 4

• dot that travels furthest is the most soluble
• dot that doesn’t move is insoluble
• if two have risen the the same spot, then they contain each other in

Question 5

calculating Rf value

Answer 5

Rf = distance moved by spot / distance moved by solvent

distance moved by spot - measured from baseline to the middle of the spot
Rf is always <1