Isa's Chemistry E-Journal 2013: Chromatography!

We did chromatography for our practical yesterday! It was really cool and an enriching experience haha. Watching the different colors go up the paper was really cool.

Basically, chromatography a type of separation technique. Paper chromatography is used to separate a mixture of solutes (solutes= a component in a solution, disolved in a solvent) with different solubility and degree of absorption. A solvent moves over an absorbent medium to separate the solutes.

As a result, solutes with a better degree of absorption will not travel up the paper (or the absorbent medium used) as high as a solute with a not so good absorption.

Things that can be separated using chromatography= Eg. Dyes in ink or a mixture or sugars (the practical we did was the dye one^^)

So how did we carry out the chromatography? First, you draw a pencil line from the edge of the paper, roughly about 1.5cm- 2cm. Then, using a capillary tube, dip it into your dye. Do not hold it there too long or else your ink drop will be too big. Next, place a drop of the ink on the line in the middle. Let it dry for a bit before repeating the step so that your drop of ink will be more concentrated.

Prepare your solvent. In this case, I used distilled water. About 1.5cm of solvent was put in a boiling tube (as the boiling tube was the right size for my chromatography paper). Try not to let any solvent go to the side of the tube. It should just be at the bottom or else it might affect your experiment.

Dip the chromatography paper into the solvent. The pencil mark should be above the water surface. The solvent will then "run up" the paper.

The principles of paper chromatography:

As solvent travels up the paper, the dyes are dissolved.
Some dyes are more soluble so they travel up the paper more quickly then others.
Some dyes are less soluble, thus they are absorbed more strongly and quickly into the paper.
Thus you can tell what colors the dye is made out of.

What caused the separation of dyes?

1. The solubility of the dyes in the solvent

2. The tendencies of the dyes to be absorbed.

3. Hence identical dyes will travel the same distance along the paper.

Retention Factor! :) (Symbol= Rf)

Unknown substances separated can be identifyied by Rf values. How do you find the Rf value? Easy! Take the distance moved by the substance and divide it over the distance moved by the solvent! (Note that you measure the distance the substance moves from the pencil line)

Chromatography is really useful, especially when you wan to separate and identify compounds in a mixture. Chromatography is even used in crime cases! They use chromatography for things like blood samples and stuff like that:) So cool right?

Pictures of my experiment now!:D