Chromatography Lesson s a process for separating components of a mixture
- 1. Needed for this lesson . • Class practical (1 set per pair) • 1 x water soluble marker (min. 2 different colours in class), 1 x 250ml beaker, 2 x cocktail sticks or wooden splints, 2 x paper clips, chromatography paper strips /filter paper (enough for one per student). • Worksheets: • 7Ed_Chromatography worksheet.
- 2. Learning objective: To be able to explain and model how to chromatography works using solubility. Chromatography (Practical Skills) Explain and model- to demonstrate and explain how chromatography works. Command word/s Lesson 5: Chromatography Unit 7E: Mixtures and Separation Tool box – key words observing and classifying Scientific Enquiry Focus Chromatography, Separation, Solubility, chromatogram, pigments Textbook: pages 80-81
- 3. Define the term chromatography Write a simple method for chromatography. Use chromatography to separate an ink and explain what happens and why. Analyse how chromatography can be used to identify substances in a mixture by solving a Mystery Case. Low Mid High Stretch Learning objective:To be able to explain and model how to chromatography works using solubility. Learning outcomes
- 4. Starter B: What is ink? How many different chemical substances do you think it contains? Starter A: What happens when Smarties get wet? What does this tell you about the colourings? Chromatography.
- 5. • Dyes and inks are often mixtures of chemical pigments dissolved in water or other solvents. • Different pigments may be mixed to make different shades. • If the pigments are water soluble the colours will run if they get wet. We can look at different pigments in a dye or ink using chromatography.
- 6. • Chromatography is used to separate inks and dyes. • It works because some substances are more soluble than others. Chromatography. • Ink is spotted onto chromatography paper. • A solvent soaks up through the paper. • Very soluble chemicals move far up the paper. • Less soluble substances do not move as far. dry paper wet paper solvent front 1 2 3 4 5 6 7 8 Chromatography Video Watch up to 1:10 Where might this be useful?
- 7. Chromatography method – gather round. Is this a good method? How might you improve it? Watch the demo and suggest improvements. 1. Draw a line on a piece of paper. 2. Place a dot of ink on the line and put the paper in a beaker. 3. Pour some water in the beaker. 4. Let the water rise up the paper.
- 8. 1. Draw a line on a piece of paper. 2. Place a dot of ink on the line and put the paper in a beaker. 3. Pour some water in the beaker. 4. Let the water rise up the paper. Chromatography method. Task: write the method you will use. Work together in your groups to rewrite this method with the extra details needed to make the experiment actually work. You have 10 minutes! Extension: diagrams like the one above often improve methods. Draw a labelled diagram to improve your method.
- 9. 1. Draw a horizontal line in pencil 2 cm from the bottom of a piece of chromatography paper. 2. Draw a spot of ink in the centre of the line. Hang the paper in the beaker so it does not touch the glass. 3. Add water to cover the bottom of the paper but below the pencil & ink spot. 4. Allow the water to rise until between ½ and ¾ of the way up the paper. • Cocktail stick • Chromatography paper • Beaker • Pencil line • Ink spot • Water Help slide. Your method should contain some of the details shown below.
- 10. Define the term chromatography Write a simple method for chromatography. Use chromatography to separate an ink and explain what happens and why. Analyse how chromatography can be used to identify substances in a mixture by solving a Mystery Case. Low Mid High Stretch Learning objective:To be able to explain and model how to chromatography works using solubility. Learning outcomes
- 11. 1. Draw a horizontal line in pencil 2 cm from the bottom of a piece of chromatography paper. 2. Draw a spot of ink in the centre of the line. Hang the paper in the beaker so it does not touch the glass. 3. Add water to cover the bottom of the paper but below the pencil ink spot. 4. Allow the water to rise until between ½ and ¾ of the way up the paper. Perform chromatography. Task: follow your own method or the one above to separate an ink. While it is separating, draw and label a diagram (if you have not already done so). Challenge question. The ink dot smudges but the pencil should not. Can you explain what this shows us?
- 12. Chromatography - what happened and why? ⮚ Look at the chromatogram you have made. ⮚ Describe what your chromatogram shows. Try to answer the following: • What happened to the ink spot? • What happened to the pencil line? • Why did they behave differently? • Did your ink contain more than one chemical? How do you know? • Did the pigments behave the same? Explain why they might have behaved differently.
- 13. Chromatography - what happened and why? ⮚ Look at the chromatogram you have made. ⮚ Things you may have noticed: ✔The ink spot spread up the paper and separated into different colours. ✔The pencil line did not move at all. ✔The chemicals in ink are soluble in water but pencil is insoluble in water. ✔The ink contained more than one chemical as it separated into several different colours. ✔The chemical pigments that moved further up the page are more soluble in water whereas those that moved slower are less soluble in water.
- 14. Mid-Plenary 1) Give a definition for the term chromatography. 2) Using the term “soluble”, explain how different chemicals separate using chromatography. 3) Arrange the following chemicals in order of how high they will rise up the filter paper, when doing chromatography. Chemical 1: Extremely soluble Chemical 2: Insoluble in solvent Chemical 3: A little bit soluble in solvent
- 15. Define the term chromatography Write a simple method for chromatography. Use chromatography to separate an ink and explain what happens and why. Analyse how chromatography can be used to identify substances in a mixture by solving a Mystery Case. Low Mid High Stretch Learning objective:To be able to explain and model how to chromatography works using solubility. Learning outcomes
- 16. http://www.youtube.com/watch?v=KAnFff4pOp4 This is important for the analysis of chromatograms. If done well enough for long enough, different substances will separate into distinct “spots”.
- 17. Interpreting chromatograms. On the chromatogram below, seven food colourings were separated to see how many pigments each contained. Plenary
- 18. Interpreting chromatograms. 1. Which food colourings contained just one substance? 2.Which colouring contained the most chemical pigments?
- 19. Interpreting chromatograms. One spot = one chemical / substance / pigment
- 20. Interpreting chromatograms. One spot = one chemical / substance / pigment Five spots = five chemicals / substances / pigments
- 21. Interpreting chromatograms. How many chemical pigments are used to make green food colouring? 3 spots = 3 chemicals
- 22. Interpreting chromatograms. Which other food colourings contain the pigment used in orange food dye? brown and yellow
- 23. Interpreting chromatograms. Which food colouring is made by mixing blue and pink food colouring? violet
- 24. Define the term chromatography Write a simple method for chromatography. Use chromatography to separate an ink and explain what happens and why. Analyse how chromatography can be used to identify substances in a mixture by solving a Mystery Case. Low Mid High Stretch Learning objective:To be able to explain and model how to chromatography works using solubility. Learning outcomes
Editor's Notes
- #4: Starter A: many students will be aware that the colours “run” when Smarties get wet. This shows that the food colourings are soluble, as they mix and spread with water. Starter B: causing students to think more deeply about an everyday substance. Some may be aware that ink is made of dissolved pigments but few are likely to appreciate that even “simple” black ink is likely to be a complex mix of different substances rather than one single pigment.
- #6: Students should note the first two points, the show video (don’t go past 1:11 as that is GCSE level detail). Students may have ideas that chromatography could be useful in police investigations – classic application would be identifying the ink used to write a death threat or ransom note. More everyday uses might be to analyse paints in possibly forged artwork or testing food colourings to see if they are made of the pigments they claim to be, rather then banned or unsafe pigments.
- #7: Demo the experimental setup. Ask students to read each step aloud before performing it and suggest what extra details are needed. Then clarify while performing the step before moving to the next step and repeating the process. Details to demonstrate: Draw horizontal line in pencil ~2 cm from bottom of chromatography/filter paper. Draw dot in ink on the centre of the line. Fold the top edge of the paper over a cocktail stick and affix with a paper clip so the paper hangs into the beaker without touching the glass bottom. Add water so the bottom of the paper is in the water but the pencil line and ink dot are above the water level. Let the water rise until it is between halfway and ¾ of the way up the paper. Remove and leave to dry.
- #8: Demo the experimental setup. Ask students to read each step aloud before performing it and suggest what extra details are needed. Then clarify while performing the step before moving to the next step and repeating the process. Details to demonstrate: Draw horizontal line in pencil ~2 cm from bottom of paper. Draw dot in ink on the centre of the line. Fold the top edge of the paper over a cocktail stick and affix with a paper clip so the paper hangs into the beaker without touching the glass bottom. Add water so the bottom of the paper is in the water but the pencil line and ink dot are above the water level. Let the water rise until it is between halfway and ¾ of the way up the paper. Remove and leave to dry.
- #9: Optional slide. If some students are struggling to replicate the method, have available on-screen or as printed copy so they can visit it for help.
- #11: Challenge: switched-on students will realise that less soluble substances do not travel very far. So if the pencil does not move at all, it must be completely insoluble in water. This is why markings are drawn in pencil, so we know where the ink started from.
- #12: This task may be best done at the start of the next lesson once chromatograms have dried and students can stick them into their books.
- #13: This task may be best done at the start of the next lesson once chromatograms have dried and students can stick them into their books.
- #17: Students can discuss and see if they can reach agreement upon answers.