Organic synthesis - Practical techniques.

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Recrystallisation

This isa methods for purifiying a solid which is in crystalline form.

Method:

1.Dissolve in a hot solvent (minimum amount) to remove soluble impurities.

2.Filter out all of the insoluble impurities from the hot solution

3. leave to cool

4. filter the cold solution

5. Wash and dry your product.

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Refluxing

  • This is where you continuously heat a reaction allowing the reacts to boil and condense to allow the reaction to go to completion. You will have used this technique in the formation of Aldehydes /ketones/carboxylic acids.This technique also helps to prevent the release of toxic fumes and allows the reaction to continue for longer

You will need

  • Pear shaped flask
  • Water condenser
  • A heating mantle
  • refluxing columm
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Melting point determination

You will need

  • Busen
  • Tripod
  • Gauze
  • Heat proof mat
  • Match
  • Thermometer
  • and 1cm of a sample to be tested in a capillary tube

you must record the temp at which the sample begins to melt and the temperatur at which all of the sample has melted, these two valu should be fairly close no more than 5 degrees apart for a practical assessment ( this is a popular topic for one for Edexcel). For substances which have a temperature which is greater than 100 degrees water cannot be used so it is changed for sand or oil.The purity of the substance can be guessed byhow close the values are because impuiies will increase the melting point and widen the range of values achieved.

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Boiling point determination

You will need

  • Busen
  • Gauze
  • Beaker
  • Heat proof mat
  • Thermometer
  •  1cm Sample in a test tube anda cappillary tube inside the sample test tube
  • Match
  • Stirrer- so you have constant temp in the beaker
  • Tripod

Record the tep wen bubbles first start o appear form the capppillary tube and the temp at which they begin to form rapidly ( a rolling boil it is sometimes called in cook books).Then leave it to cool recording the temperature that the bubbles stop. All of these temperatures should be pretty close together.Problems can occur with accuracy because you measure the temp of the water and assume that the temp is the same in the sample tube.The points are hard to judge as well. Instead you could use fractional distillation instead.

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steam distillation

This technique  is   used to remove essentail oils from oranges and lemons. You have to pass steam through the mixture and add water after this you boil the mixture and distill off the product that you want.

you need

  • A water condenser
  • Heat source
  • collection vessel
  • reflux condenser
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