Mixtures and Chromatography

Unlike in a compound, there’s no chemical bond between the different parts of a mixture
The parts of a a mixture can be either elements or compounds, and they can be separated out by physical methods such as filtration, crystallisation, simple distillation, fractional distillation and chromatography
Air is a mixture of gases, mainly nitrogen, oxygen, carbon dioxide and argon
Crude oil is a mixture of different length hydrocarbon molecules
The properties of a mixture are just a mixture of the properties of the separate parts-the chemical properties of a substance aren’t affected by it being part of a mixture * For example, a mixture of iron powder and sulfur powder will show the properties of both iron and sulfur. It will contain grey magnetic bits of iron and bright yellow bits of sulfur.

One method of separating substances in a mixture is through chromatography. This techniques can be used to separate different dyes in an ink. Here’s how you can do it:
Draw a line near the bottom of a sheet of filter paper. * Use a pencil to do this-pencil marks are insoluble and won’t dissolve in the solvent.
Add a spot of the ink to the line and place the sheet in a beaker of solvent, e.g. water.
The solvent used depends on what’s being tested. Some compounds dissolve well in water, but sometimes other solvents, like ethanol, are needed.
Make sure the ink isn’t touching the solvent-you don’t want it to dissolve into it
Place a lid on top of the container to stop the solvent evaporating
The solvent seeps up the paper, carrying the ink with it
Each different dye in the ink will move up the paper at a different rate so the dyes will separate out. Each dye will form a spot in a different place-1 spot per dye in the ink
If any of the dyes in the ink are insoluble(won’t dissolve) in the solvent you’ve used, they’ll stay on the baseline
When the solvent has nearly reached the top of the paper, take the paper out of the beaker and leave it to dry
The end result is a pattern of spots called chromatogram