C1.4 Fractional Distillation and Chromatography
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What separating technique is needed to separate different liquids with similar boiling points?
➢ Fractional distillation
How does a fractionating column aid separation of ethanol and water?
➢ The temperature in the column is highest at the bottom ➢ A substance with a higher boiling point will condense more readily on the cooler glass beads nearer the bottom of the column ➢ Then drip back down into the flask beneath ➢ The substance with lower boiling will continue rising and pass into a condenser and can be collected
What is the boiling point of ethanol?
➢ 78 degrees
What is the boiling point of water?
➢ 100 degrees
What liquid would be collected in a mixture of ethanol and water?
➢ Ethanol because it has a lower boiling point
What is ethanol used as?
➢ A biofuel
What technique is needed to separate substances from mixtures in a solution?
➢ Chromatography
What is the 1st step in paper chromatography?
➢ Use a capillary tube to dab a spot of the solution on a pencil line near the bottom of the sheet
What is the 2nd step in paper chromatography?
➢ Paper placed in a solvent at the bottom of a beaker
What is the 3rd step in chromatography?
➢ Allow the solvent to soak up the paper running through the spot of the mixture
What can the Rf value be useful for?
➢ Identifying unknown chemicals if they can be compared to a range of reference substances
How do you calculate the Rf value?
➢ Distance travelled by the substance/ Distance travelled by the solvent
What is the stationary phase?
It is the paper