Chromatography

Question 1

paper chromatography method

Answer 1

1. draw a line near the bottom of a sheet of filter paper to make the baseline (pencil must be used for this as it is insoluble so it won’t dissolve in the solvent)
2. add spots of different inks to the line at regular intervals
3. loosely roll the sheet up and put in beaker of solvent
4. the solvent used depends on what is being tested
5. make sure the level of solvent is below the baseline as you don’t want the inks to dissolve into the solvent
6. place a lid on top of the container to stop the solvent evaporating
7. the solvent will move up the paper
8. each different dye in the inks will move up the paper at a different rate and form a spot in a different place
9. when the solvent has nearly reached the top of the paper, take paper out of the beaker and leave to dry
10. the end result is a pattern of spots called a chromotogram

Question 2

how does chromatography separate mixtures?

Answer 2

• chromatography works because different dyes will move up the paper at different rates
• some will stick to the paper and others will dissolve more readily in the solvent and travel more quickly
• the distance the dyes travel up the paper depends on the solvent and the paper you use

Question 3

how to calculate Rf value

Answer 3

Rf = distance travelled by solute/distance travelled by solvent

• to find the distance travelled by the solute, measure from the baseline to the centre of the spot