CHEMISTRY A2 experimental techniques

desciption of some of the experimental techniques for a2 chemistry:

  • recrystallisation
  • colorimetry
  • paper chromatography
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Recrystallisation

  • WHAT IS THE PURPOSE OF RECRYSTALLISATION?
  • WHAT IS THE PROCEDURE OF RECRYSTALLISATION?
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Recrystallisation

Purpose: Purify an impure solid

Procedure:

  • Dissolve the impure solid in a MINIMUM volume of an appropriate solvent
  • Allow to cool and recrystallise
  • Collect crystals by vacuum filteration using a buchner funnel
  • Rinse with cold solvent
  • Allow to dry

Check purity by melting point test

Solid must be SOLUBLE in solvent BUT insoluble when cold

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Colorimetry

  • WHAT IS THE PROCEDURE OF COLORIMETRY?
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Colorimetry

Procedure:

  • Choose a suitable filter (complementary colour)
  • Zero/ reference with pure solvent
  • Dilute 'known solution' to range of known concentrations and measure the absorbance
  • Plot a calibration curve: concentration vs. absorbance
  • Measure absorbance of unknown concentration solution and use calibration curve to work out the concentration
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Paper Chromatography

  • WHAT IS THE PROCEDURE OF USING PAPER CHROMATOGRAPHY?
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Paper Chromatography

Procedure:

  • Draw line near bottom of paper.
  • Pure amino acid samples are placed on line.
  • Paper is placed in a solvent in a container, making sure that the line is above the solvent.
  • Place lid on top of container.
  • Wait for solvent to rise and mark where it rises to.
  • Spray the chromatogram with ninhydrin and heat.
  • Compare Rf values.
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Comments

jane smith

Really clear, really concise - THANK YOU!!!

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