Chromatography Flashcards
Define insoluble
It won’t dissolve in a solvent eg:water therefore will not move up the paper with the solvent.
Define RF value
An RF value is a value of how far the ink travelled compared to how far the solvent travelled.
What is the equation for an RF value?
the distance moved by solvent
How do you know when an ink is soluble?
When an ink travels up the paper you know it is soluble.
How do you know when an ink is insoluble?
When an ink does not travel up the paper you know it is insoluble.
How do you change an insoluble to a soluble?
You can change it to a pigment which is more soluble.
Why does the pencil line have to be pencil?
Because pen is soluble in water and would travel up the paper which would make the experiment invalid whereas pencil is insoluble in water and won’t move up the paper with the solvent.
Why must the solvent line be lower than the pencil line?
It must be lower than the pencil line because if it was above then the ink dots would dissolve into the solvent therefore not moving up the paper.
What do you know if the ik dot stays the same?
If it stays as the same colour then you know that it was only made up from one pigment
What do you know if it separates into 2 or more spots?
You know that it was made from 2 or more pigments and they all have different solubilities/RF values which means they separate at different rates.
Define chromatography.
Chromatography is a method used to separate colours by dissolving them in a solvent using ink, chromatography paper, a beaker and a solvent (water)
What is the method for chromatography?
1) Take some chromatography paper and with a ruler, draw a very faint line along the bottom of the paper IN PENCIL!
2) Make sure that your line is above the level of solvent so the dyes travel upwards.
3) Repeatedly dab the first ink on the same place on the pencil line to build up the coloured dot.
4) Repeat this for the rest of the inks along the line so that each of the dots occupies its own strip.
5) Curl your paper into as cylinder and fasten with a paperclip.
6) Wait for the ink to dry.
7) Pour a small amount of the solvent, eg: water, into a clean, dry beaker ensuring that the level of solvent is lower than the pencil line on the chromatogram.
8) Carefully stand the cylindrical chromatogram in the beaker of solvent, ensuring that the paper DOES NOT TOUCH THE SIDES OF THE BEAKER.
9) Once standing, leave it in the solvent and remove it just before the solvent front reaches the top of the paper.
10) Wait for it to dry then remove the paperclip and with a pencil and a ruler, mark on the line of the solvent front (where it got to)
How do you know if 2 pigments are the same?
If 2 pigments are the same they will travel the same distance and also have the same RF value and solubility in that solvent.
How do you know if 2 inks are the same?
If 2 inks are the same they must travel the same distance and also have the same amount of dots.
What is the link between solubility of an ink and distance moved with the solvent?
The more soluble the ink, the further it will travel.
