core practical: investigating inks

• Core Practical: Investigating Inks

  1. Aim: Investigate how simple distillation and paper chromatography can be used to separate and identify a mixture of food colourings

  2. Part 1 - Simple Distillation: Separate solvent from dyes by distillation

  3. Part 2 - Paper Chromatography: Separate and identify dyes using paper chromatography

  
• Ink


  • Consists of a solvent which has different dyes dissolved in it
• Simple Distillation


  1. Add anti-bumping granules

  2. Heat gently so as not to go past the boiling point

  3. Record the temperature of boiling point
• Solvents


  Tend to have lower boiling points than the dyes which tend to be more viscous, so they will evaporate first
• Dyes


  Tend to be more viscous than the solvents
• Paper Chromatography


  1. Draw a horizontal pencil line 2 cm from the end of the chromatography paper

  2. Use a different capillary tube to put a tiny spot of each colouring A, B, C and D on the line

  3. Use the fifth tube to put a small spot of the unknown mixture U on the line

  4. Make sure each spot is no more than 2-3 mm in diameter and label each spot in pencil

  5. Pour water into the beaker to a depth of no more than 1 cm and clip the top of the chromatography paper to the wooden spill

  6. Carefully rest the wooden spill on the top edge of the beaker, with the bottom edge of the paper dipping into the solvent

  7. Allow the solvent to travel undisturbed at least three quarters of the way up the paper

  8. Remove the paper and draw another pencil line on the dry part of the paper as close to the wet edge as possible (solvent front line)

  9. Measure the distance in mm between the two pencil lines (distance travelled by the water solvent)

  10. For each of food colour A, B, C and D measure the distance in mm from the start line to the middle of the spot

  
• The pencil line must never be below the level of the solvent as the samples will be washed away
• Rf value


  The ratio of the distance travelled by the solute to the distance travelled by the solvent
• Hazards, risks and precautions should be considered when carrying out the practical