Purification and Chromatography

A pure substance:
- Is made up of only one substance
- Is not mixed with another substance
- Can be determined by checking its melting and boiling point, or by using chromatography

- Has an exact and constant melting point.
- Will melt at completely at one temperature, if it is a solid
- The greater the amount of impurities, the lower the melting point
- Has an exact and constant boiling point
- The greater the amount of impurities, the higher the boiling point of the liquid

Chromatography:
It is the technique of using a solvent to separate a mixture into its compounds.
It is used to:
- Separate the components in a sample.
- Identify the number of components in a sample.
- Identify the components present in a sample.
- Determine whether a sample is pure.
It depends on solubility of compounds or substances in a solvent.

1) A spot of food coloring is applied to the chromatography paper.
2) Once the paper is dipped into the solvent, ethanol, it souls up the ethanol.
3) Ethanol dissolves the dye. It continues to travel up the paper, carrying the dyes along.
4) A dye that is not very soluble in ethanol will be carried far along the paper.
5) A dye that is very soluble in ethanol will be carried far along the paper.
6) Colored spots are left in different places on the paper at the end of the experiment.
A pure sample gives only one spot on the paper.

Rƒ+= Distance travelled by the substance ÷ distance travelled by the solvent

Example: The Chalk Experiment
The slower it moves up the chalk, the less soluble it is. (Green)
The faster it moves up the chalk, the more soluble it is. (Red)
As it is highly soluble in water, the red ink prefers to stay in water and will travel up the chalk with the water.
As it is less soluble, the red ink will prefer to stay on the chalk and will not move up as quickly with the water level.