1. Today’s aims Understand what chromatography is. Understand how chromatography used in everyday life 10 December 2013 Today’s Title: Chromatography

2. All: Will be able to… C Grade: Describe how paper chromatography can be used to separate and identify components of mixtures, including colouring agents in foodstuffs Most: Will be able to… B Grade Evaluate the information provided by paper chromatograms, including the calculation of Rf values, in a variety of contexts, such as the food industry and forensic science Some: Will be able to… A Grade Explain why published R f values are sometimes different to experimental values.

3. Key words for today’s lesson Solvent Solution Solubility Chromatography Chromatogram Rf value Remember you have a glossary with these words in it!

5. Paper chromatography Simple chromatography is carried out on paper. A spot of the mixture is placed near the bottom of a piece of chromatography paper and the paper is then placed upright in a suitable solvent, e.g. water. As the solvent soaks up the paper, it carries the mixtures with it. Different components of the mixture will move at different rates. This separates the mixture out.

6. Chromatography – a separation technique Chromatography can be used to separate mixtures of coloured compounds. Mixtures that are suitable for separation by chromatography include inks, dyes and colouring agents in food.

7. Paper Chromatography 1.What’s happening in these diagrams? 2.What happens to the solvent after 10 minutes? 3.What happens to the ink spots?

8. Have we done this before? Yes! We separated the different pigments found in green leaves.

9. Rf values Different chromatograms and the separated components of the mixtures can be identified by calculating the Rf value using the equation: Rf = distance moved by the compound ÷ distance moved by the solvent The Rf value of a particular compound is always the same - if the chromatography has been carried out in the same way. This allows industry to use chromatography to identify compounds in mixtures.

10. Rf = distance moved by the compound ÷ distance moved by the solvent The SOLVENT has travelled 7.7cm COMPOUND (The brown dye) has travelled 4.1cm Rf= 4.1 / 7.7 Rf = 0.53

11. Task 1 – Chromatography experiment

12. Plenary: True or False? A substance that dissolves is water is soluble. True A solvent is a solid that dissolves in water. False Water is the only solvent. False Chromatography can be used to identify colours in foodstuffs. True Chromatography can only be used to identify coloured substances. False Chromatography can be used to solve a crime. True

13. Solvent – able to dissolve other substances Solution – a solvent and a solute mixed together Solubility – the maximum amount of solute dissolved in solution Chromatography – a technique used to separate mixtures Chromatogram – the diagram formed as a result of chromatography Rf value – a number calculated to show how far a solute has travelled. What have we learnt so far?

14. Learning objectives – achieved? Describe how paper chromatography can be used to separate and identify components of mixtures, including colouring agents in foodstuffs Evaluate the information provided by paper chromatograms, including the calculation of Rf values, in a variety of contexts, such as the food industry and forensic science

15. Your notes Make a mind map of the different types of separation techniques that you have learned about. – Miscible and immiscible liquids – Fractional distillation of gas – Chromatography Use the revision guides and textbooks to help you summarise these techniques. You need to know these for your exam.