Atoms - Continued

Atoms - Continued

1.7  describe experimental techniques for the separation of mixtures, including simple distillation, fractional distillation, filtration, crystallisation and paper chromatography

i) Simple distillation 
As the components of a mixture are not chemically bonded, they can be separated by physical means. Simple distillation is used to separate out a liquid from a solution. It can only be used to separate things with very different boiling points. Things with similar boiling points must be separated using fractional distillation. 

Process;
1) The solution is heated, causing the part of said solution with the lowest boiling point to evaporate.
2) The vapour will then be cooled until it condenses and turns back into a liquid, when it will be collected. 
3) The remainder of the solution will be left behind in the flask or container.

The process of simple distillation.

ii) Fractional distillation

Fractional distillation is used to separate a mixture of liquids with very different boiling points. 

Fractional distillation of crude oil 

1) The crude oil is heated until most of it has turned into gas. The gases then enter a fractionating column while the bitumen (liquid part) is drained off at the bottom.

2) There is a temperature gradient within this column, in which it is hot at the bottom and gets gradually cooler as you go up. When a certain substance of the crude oil reaches the part of the column where the temperature is lower than it's own boiling point, they condense and turn back into a liquid. 

3) When the first liquid has been collected, you raise the temperature until the next one reaches the top and condenses also. 

Diagram showing the 

iii) Filtration

Filtration is used to separate an insoluble solid from a liquid. It is the process of separating an undissolved solid from a mixture of that solid and a liquid/solution. It is done through simply pouring the solution into a beaker through a barrier, often filter paper, which will leave the solid in the paper as the liquid solution travels past the filter paper into the beaker it is being poured into. 

Process of filtration. 

iv) Crystallisation 

Crystallisation is used to separate a soluble solid from a solution. It is the process of separating a dissolved solid from a solution. 

Process; 

1) Pour the solution into an evaporating dish

2) Heat the solution slowly, this will cause some of the solvent to evaporate and the solution will become more concentrated. Stop heating the solution when crystals start to form. 

3) Remove the dish from the heat, leaving it in a warm place to allow for the the rest of the solvent to evaporate. This will encourage large crystals to form.

4) Lastly, dry the product. This can be done by using a drying oven or a desiccator (contains chemicals that remove water from the surroundings.) 

Diagram showing the process of crystallisation. 

v) Paper chromatography

Paper chromatography is used to separate out mixtures of dyes. It works because different dyes move up the paper at different rates.

Process; 

1) Draw a line near the bottom of a sheet of filter paper, using a pencil as pencil marks are insoluble and will not react with the solvent. 

2) Add spots of each different dye to the line at regular intervals.

3) Roll up the sheet of paper and put in the beaker of solvent. However, make sure the dyes are not touching the solvent as they could dissolve in it if this happens.

4) Place a lid on the top of the container to stop the solvent evaporating. 

5) The solvent will then seep up the paper, carrying the dyes with it.

6) Each different dye that is present within the solvent will move up the paper at a different rate and form a mark in a different place. 

7) The end result will be a pattern of spots known as a chromatogram. 

1.8 explain how the information from chromatograms can be used to identify the composition of a mixture. 

The information from chromatograms can be compared to reference materials in order to identify the composition of a mixture. The reference materials will be chromatograms for some dyes that you think may be in the ink. If you compare these, you will see what dyes match up and therefore what dyes are present in the composition of your mixture.