Recrystallisation

revision cards on each step of recrystallisation

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  • Created on: 24-01-11 19:03

Choosing a solvent

  • Choose a solvent that the impure substance is NOT soluble in a LOW temperatures but is COMPLETELY soluble in at HIGHER temperatures. 
  • Add as small amount as possible.(http://janus.ucc.nau.edu/~jkn/235A-Appendix_files/image006.jpg)
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Heating

  • Once the solvent has been added to the impure substance, heat the mixture until the impure solid has completely dissolved
  • A water bath or bunsen burner could be used for this(http://www.rsc.org/images/CLASSIC-KIT-200_tcm18-99904.jpg)
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Cooling

  • Cool the solution until crystals have formed
  • You could cool it in an ice bath
  • If crystals don't form then too much solvent may have been used.
  • So allow some of the solvent to evaporate and then heat the solution again and re-(http://1.imimg.com/data/D/N/MY-778583/copper-sulphate-crystal_250x250.jpg)cool.
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Vacuum filtration

  • Wash the crystals with cold solvent
  • Pour the solution/crystals into the Buchner funnel and turn on the vacuum pump.
  • The part you want to keep is the solid that hasn't passed through the funnel.
  • Dry the solid, this can be just left in the air to dry(http://mongoose.wraithsys.net/~cisco/c121/images/vacuum.gif)
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