Please enable JavaScript.
Coggle requires JavaScript to display documents.
2.2.4 Core Practical - Investigating Inks - Coggle Diagram
2.2.4 Core Practical - Investigating Inks
Aim
Investigate how simple distillation and paper chromatography can be used to separate and identify a mixture of food colourings
Part 1 - Simple Distillation
The solvent must first be separated which can be done by simple distillation
Solvents tend to have low boiling points than the dyes which tend to be more viscous so it will evaporate first.
The investigation must thus include analysis of both the solvent and the dyes used
Add anti-bumping granules and heat gently so as not to go past the boiling point
Ink consists of a solvent which has different dyes dissolved in it
Record the temperature of boiling point
Part 2 - Paper Chromatography Materials
A wooden spill
A rectangle of chromatography paper
Four known food colourings labelled A–D
An unknown mixture of food colourings labelled U
Five glass capillary tubes
Paper clip
Ruler & pencil
A 250 cm^3 beaker
(look at comments)
Practical Tip
The pencil line must never be below the level of the solvent as the samples will be washed away
Method
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. The top end is the furthest from the spots
Carefully rest the wooden spill on the top edge of the beaker. The bottom edge of the paper should dip into the solvent
Make sure each spot is no more than 2-3 mm in diameter and label each spot in pencil
Allow the solvent to travel undisturbed at least three quarters of the way up the paper
Use the fifth tube to put a small spot of the unknown mixture U on the line
Remove the paper and draw another pencil line on the dry part of the paper as close to the wet edge as possible. This is called the solvent front line
Use a different capillary tube to put a tiny spot of each colouring A, B, C and D on the line
Measure the distance in mm between the two pencil lines. This is the distance travelled by the water solvent
Use a ruler to draw a horizontal pencil line 2 cm from the end of the chromatography paper
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
Results
Evaluation
The Rf values of food colours A, B, C and D should be compared to that for the unknown sample as well as a visual comparison being made
Conclusion
The use of chromatography and Rf values is a viable method of identifying unknown mixtures given reference material
Table
(look in comments)