Chromatography Flashcards
What category is Chromatography in?
Methods of separation
What is paper chromatography used for?
To separate dyes - e.g. inks, paints, food colourings
What is chromatography used for?
To separate out mixtures.
How do you carry out paper chromatography?
1) Draw a baseline near the bottom of the paper.
2) Add different ink spots to the line at regular intervals.
3) Loosely roll the sheet and place in a beaker with a solvent.
4) Make sure the solvent level is below the baseline.
5) Place a lid on the container.
6) The solvent will rise, carrying inks with it.
7) Wait for the solvent to nearly reach the top and then take out the paper and leave to dry.
What should the baseline be drawn with, and why?
Pencil as the marks are insoluble so it won’t dissolve in the solvent.
State a liquid that is commonly used as a solvent in paper chromatography:
Water or Ethanol
Why must the solvent level be below the baseline?
So that the inks do not dissolve into the solvent
Why is a lid used?
To stop the solvent from evaporating.
What is the end pattern on the paper called?
Chromatogram
State what is commonly used as a lid.
Watch glass
Why would a dye likely not move up the paper?
Because it is non-soluble in the current solvent.
What should be done if a dye does not move from the pencil line?
Find a new solvent as this dye is non-soluble in the current one.
What should be done if a dye moves up the paper with the solvent front?
Find a new solvent as this dye is too soluble in the current one.
What is the affinity of a dye?
How well the dye ‘sticks’ to a paper.
If there are 3 spots created by the dye up the paper, what can be said about the number of different dyes present in the spot?
There are at least different dyes, it is possible that one of the spots is made form more than one colour.
Where is the distance moved by an ink measured from?
The middle of the ink spot to the base line
What does Rf stand for?
Retardation Factor
What is the Retardation Factor?
A ratio of distance travelled by the spot and the distance travelled by the solvent.
What are the boundaries that an Rf vale has to be within?
0 and 1.
What is the equation for Rf?
Distance moved by a spot (from baseline) /
Distance moved by solvent front (from baseline)
What are the units for an Rf value?
Rf has no units
Suggest why the Rf has no units?
It is simply a ratio.
What are Standard Reference Materials? (SRM’s)
Pure substances which have controlled concentrations and purities. They are often run against a mixture to check for the identities of its components.
Why does chromatography work?
Different dyes will move up the paper at different rates.
