7H Solutions Lesson 6

7H Solutions
Lesson 6: Chromatography
Learning objectives
 That a mixture of two or more solutes which are soluble in a particular solvent
can be separated by chromatography
Learning outcomes
 Use chromatography to separate and identify different dyes.
 Use particle theory to explain how chromatography works.
 Interpret chromatograms, explaining what the evidence shows.
For demonstration: “Ransom note” written with one of the test pens belonging to the
For Class practical: strips of filter paper, three suspects’ pens.
Lesson Outline
1. Demonstrate the separation of dyes in Quink black ink by chromatography.
2. Practical: Who wrote the note?
Pupils obtain spots from three pens and produce chromatograms to see
whose pen wrote the note.
Hold up a “ ransom note” that was previously prepared using one of the black
pens used. Prepare a chromatogram by tearing of a section of the note and
get pupils to describe what they see (number of dyes in the mixture, colours
of dyes in mixture). Pupils then take strips of filter paper and mark using each
of the suspects’ pens in turn. Their task is to identify the kidnapper (Based on
example given on P32-33 of Eureka book1). They could perhaps prepare a
report to be used in court to convict the perpetrator of this heinous crime.
3. Explanation: Water creeps up the paper as soon as it is placed in the beaker.
The most soluble dye is carried faster and travels further up the paper with the
water. You could perhaps model this by having pupils acting our roles of
water and solute particles – the levels of attraction determining how far the
solute particles will go with the water particles.
4. Notes: based on explanation (missing words?). Identify most soluble dye as
the one that has travelled furthest with the water
5. Question. Eureka book 1 P.33
Plenary: go through answers to questions to give immediate feedback.