C2. Experimental techniques

Paper Chromatography

• Is a method used to separate and distinguish the substances within a mixture.
• Is used to separate the colouring agents and dye in products like food and ink.
• How it works:
• The mixture you want to separate is placed on the edge of strip of paper, right above the water. In this case, it is a black ink spot.
• The strip of paper is then dipped in the solvent (water).
• The water level slowly rises, taking the dye molecules with it.
• Depending on how strong the attraction is between the dye molecules and the water, it will move more slowly or quickly as the water level rises.
• If the ink is a mixture of two or more dyes, then the different colours will move at different rates.
• This separates the different components of ink, allowing us to identify the colours used.
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Filtration

• Is a method of separation used to remove undissolved solids from liquids.
• How it works:
• Here, filter paper and a glass funnel is used to separate the solid from the liquid.
• The filter works by allowing the liquid to flow through the paper, but not the solid.
• This is because the particles of the solid are too big to pass through the minute holes in the filter paper.
• At the end of the filtration, you are left the residue of the solid on the filter paper and the liquid in another container.
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Crystallization

• Is used to separate dissolved solids from liquids, unlike filtration.
• How it works:
• The solution is heated in an open container.
• This allows the solvent to evaporate, leaving us with a saturated solution.
• The saturated solution is a solvent which contains as much of the solid dissolved within it.
• The saturated solution is left to cool.
• At this point, crystals of the solid will grow in the solution.
• When the solution has completely evaporated, you are left with the crystallized solids.
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Distillation

• Is a method of separation used to extract a pure liquid from a mixture.
• How it works:
• In this example, we will use a mixture of both ethanol and water.
• The mixture is first heated in a round bottomed flask.
• The fact that ethanol has lower boiling point is crucial.
• At 78oc, the ethanol will evaporate into vapour.
• At this point, the vapour will travel down the condenser filled with cool, running water and be cooled down into a liquid.
• The ethanol liquid (distillate) will be collected into a beaker whilst the water is left in the flask.
• The ethanol is now separated from the water.
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Fractional distillation

• Is similar to the normal distillation method above.
• Separates a liquid mixture into its individual components
• How it works:
• The diagram uses the example of crude oil.
• Like distillation, the mixture is heated and evaporated.
• The substances within the crude oil have different boiling points and they each evaporate at different temperatures.
• The temperature decreases as the gases go up the fractioning column.
• The smaller molecules condense at the higher portions of the column at lower temperatures.
• Conversely, the larger molecules sink to the bottom and condense at higher temperature
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The importance of purity in substances

• Purifying and separation methods allow us to obtain specific substances and chemicals needed for our everyday life. Like above, the separation of crude oil into its components is essential, as the petrol allows us to keep our cars running and the naphtha is used for making plastics.
• Purifying chemicals and substances is important, especially if we ingest it. Impurities in things like drugs and food could be potentially hazardous and detrimental to our health if swallowed.