| What does Chromatography achieve? | This is a method that is used to separate and identify substances in a mixture |
| What are the 'two' phases of Chromatography | You have the
Mobile Phase [Molecules can move. This makes it usually a Gas or a Liquid]
Stationary Phase [Molecules can't move. This makes it usually a Solid, or a really Thick Liquid. |
| How does it work with Chromatography? | 1. The parts of the mixture separate themselves outwards as the mobile phase moves over the stationary phase. They all end up in different places on the Stationary Phase
2. This happens because the chemicals will spend different amounts of time dissolved in the Mobile Phase and stuck in the Stationary Phase |
| What does the speed of the chemical through the Stationary phase depend on? | This depends on how it can distributes itself between said two phases. |
| What are the two phases in Thin Layer Chromatography? | The Mobile Phase = Solvent [Ethanol for example
The Stationary Phase = Thin layer of a solid [silica gel or aluminium powder] on a Glass or Plastic plate. |
| How to set up Thin Layer Chromatography | 1. Draw a line, near the bottom of the plate [Pencil] Then put a Spot of the Mixture that is separated on the line
2. Put your Solvent into a Beaker. Dip the bottom of the Plate [Not the Spot] into the Solvent.
3. Put a watch Glass over your Beaker, to ensure the solvent wont evaporate away.
4. The Solvent will slowly go up the plate. The chemicals in the mixture dissolve in the Solvent and also move up
5. You will see then that the different chemicals in your sample separate out, making spots at different parts of the Plate
6. Now remove the Plate from the Beaker before the Solvent reaches the top. Make the Distance it has travelled [Pencil] |
| What do the amount of time spent in each phase depend on? | -How soluble they were
-How attracted they are to the Stationary Paper |
| What will happen to a chemical if its highly soluble in the solvent and therefore less attracted to the Stationary phase? | It will spend more time with the Mobile phase, meaning its going to be carried further up the Plate |
| Why Pencil markings, and not Pen's markings? | Pencil marks are insoluble and won't move with the Solvent, while solvent Pen has a chance. |
| What is Paper Chromatograph? Are there any differences | Paper Chromatography is really similar to Thin Layer Chromatography but:
-The Stationary Phase is a sheet of Chromatography paper [Filter Paper often]
-The Mobile Phase is a solvent [Exactly like Thin Layer Chromatography] |
| What is the result of a Chromatography analysis called? | A Chromatogram |
| What happens if the spots are Colourless? | Simply use a Locating agent to show where they are.
Or you can spray it the Chromatogram with a special reagent. |
| What does Rf values mean? | This measures really if the substance was pure, or not. If the Rf value doesn't match, its impure. If it does, Its pure. |
| How can you calculate Rf values? | ......Distance Travelled by Solute
. Rf=--------------------------------------
........Distance Travelled by Solvent |
| How can Chromatography be a Purity test? | Pure substances in Chromatography will not be separated into different blobs. It will always stay as one.
Impure substances will have different located blobs |
| What are the two phases in Gas Chromatography? | The Mobile Phase = Unreactive Gas [Nitrogen]
Stationary Phase = Viscous [Thick] Liquid [Oil] |
| What State do the substances need to be in? | Gas State. If not it has to be Vaporised |
| Explain how Gas Chromatography works | 1. The Mixture you are trying to find out gets injected into a long tube, that is coated inside with the Stationary Phase.
2. The Mixture moves along the tube, until it reaches the end and comes out.
3. The Time it took for a chemical to escape is recorded.
4. Each Chemical has a Different time that it escaped. |
| What is the time taken for the Chemical in Gas Chromatography | This is called the Retention Time |
| How is the Chromatogram represented? | This is represented on a Graph |
| Explain how the Chromatogram in Gas Chromatography is set out, and what it says. | -The distance on the X axis show the Retention Time. This time can be looked to see what Chemical it was
-The relative areas under the peak can show you how much the amount of chemical in each sample
-In a Pure substance, there will be only one Peak, because there is only one Chemical. |
