Chapter 3: Separation Techniques

1. Chapter 3: Separation Techniques Click to add subtitle

2. 3.1 Chromatography • Chromatography is a technique of using a solvent to separate a mixture into its components • Example: Paper Chromatography • Paper chromatography can be use to separate dyes in ink, amino acids obtain from proteins, identify toxics

3. How does chromatography works? • A spot of food colouring is applied to chromatography paper • Once the paper is dipped in ethanol, it soaks up. • Ethanol travel up the paper, carrying dyes along • Dye that is not very soluble > carried not far • Dye that is soluble > Carried far

4. How can we identify a banned substance present in food colouring? • Chromatography was performed on a sample of food colouring (‘X’) and 4 banned dyes (‘A’, ‘B’, ‘C’, ‘D’) • If X contains any of the 4 banned dyes, itt is not safe to be consumed.

5. Interpreting Chromatography • Chromatography paper with separated component is known as chromatogram Solvent front The chromatogram shows the food colouring used in the experiment was a mixture of two dyes. Coloured spots

6. Interpreting Chromatography • Chromatography paper with separated component is known as chromatogram Solvent front The chromatogram has only a spot, this dye is made up of a dye. Thus, it’s pure.

7. What conclusion can be drawn from this chromatogram? • Identical dyes produce spots at same height • Sample X does not contains the banned dyes A,B,D • However, X contains the banned dye. Therefore, it must not be consumed B X A C D

8. What conclusion can be drawn from this chromatogram? • Dyes A&D are pure • Both dye B & C are mixture of 2 different dyes • Sample X is a mixture of 3 dyes B X A C D

9. How do we identify colourless substances? Chromatography can also be used for colourless substances such as amino acids. To separate and analyse colourless substance, we apply a locating agent on a chromatogram. If no dye appear after using locating agent, this means that solvent can’t dissolve the dye

10. Uses of Chromatography • Separate the components in a sample • Identify number of components in a sample • Identify the components present in a sample • Determine whether if a sample is pure

11. Take Note: • Why do we use pencil? • Pencil is insoluble in solvent • Solvent used cannot above the pencil line. Pencil line

12. Separation Techniques Besides chromatography, there are other techniques to separate mixtures. • A solid from liquid – sand + water : Filtration • Solids – Sand + Iron Fillings : Magnetic Attraction • Liquids – Fractional Distillation • A liquid form a solution – Distillation

13. Separating insoluble solid from liquid - Filtration We can use filtration to separate solid particles from a liquid (often it is water) Example of Small Solid particles includes sand, clay, dust particles and precipitates Residue Filter Paper Filtrate

14. Separating insoluble solid from liquid – Evaporation to Dryness To recover salt from salt solution, we evaporate the solution to dryness Salt Solution Evaporating Dish

15. Separating insoluble solid from liquid – Crystallisation When a substance decomposes on heating or can lose its water of crystallisation, we do not evaporate it to dryness, we crystallise it. Sugar Decomposes on heating

16. How do we purify by crystallisation? In crystallisation, water is removed by heating the solution. Heating is stopped at the stage when a hot saturated solution is form. If the resulting solution is allowed to cool to room temperature, the dissolved solid will be formed as pure crystals.

17. How do we test for a saturated solution? • A clean glass rod can be used to test whether a solution is saturated. • It is dipped into the solution and removed. There will be a small amount of solution on the rod • If small crystals form on the rod as the solution cools, the solution is saturated • We say the solution is at is saturated point or crystallisation point • Saturated points = maximum amount of solute in solvent at certain room temperature.

18. Separating Solids (E.g.: Salt and Sand) Methods: By adding a suitable solvent and filtration Pour some distilled water (dissolve the salt) into mixture of common salt and sand. Stir and warm (to speed up whole dissolving processes) Filter the mixture Sand (Residue) Salt (dissolved) + Water [Filtrate]

19. Separating Solids (E.g.: Salt and Sand) Methods: By adding a suitable solvent and filtration 3. Wash the residue (remove salt solution, get rid of salt) with a little distilled water to remove all salt solution from it. Residue = Sand 4. Evaporate the filtrate to dryness. Salt is recovered Sand (Residue) Salt (dissolved) + Water [Filtrate] Note: If is sugar, continue up till step 3. As for step 4, it will be crystallisation.

20. Separating a Liquid from a solution • When a solid dissolves in a solvent, a solution is formed (i.e.: Salt solution) • A pure solvent can be separated from a solution by simple distillation • Distillation is the process of boiling liquid and condensing vapour. • For example, pure water can be obtained from salt solution by this process • To collect solute from solvent, we evaporate solvent.

21. How does simple distillation work? • In the distillation flask, water boils and enter condenser • In the condenser, water vapour condenses. • Pure water is collected as the distillate • Boiling chips in the flask is used to smoothen boiling. 2 1 3

22. Things to take note when doing.. • Thermometer: Should be placed beside the side arm of distillation flask. (Temperature of thermometer = Boiling point of solvent) • Condenser: Consists of 2 tubes : Inner tube and outer wet jacket. Cold running water enters from bottom of condenser and leaves from top. If the distillate is volatile, the receiver can be put in a large container filled with ice which helps keep temperature of distillate so that it remains in liquid state.

23. Separating Miscible Liquids – Fractional Distillation • Unlike oil and water, ethanol and water mix together completely to form a solution. They are said to be miscible • If two liquids are miscible, they must be separated by fractional distillation.

24. Separating Miscible Liquids – Fractional Distillation A fractionating column, is attached to the round-bottomed flash and the condenser for fractional distillation. Many glass beads in the fractionating column provide a large surface area for vapour to condense on. Other than glass beads, a fractionating column may be filled with plates or a spiral

25. Example of mixture of 2 liquids • Ethanol and water are soluble in each other • To separate these 2 miscible liquid, we use fractional distillation • The boiling point of ethanol is 78 ℃while the boiling point of water is 100 ℃ • In fractional distillation, liquid with lower boiling point(ethanol) will be collected first

26. How does fractional distillation work? • In the distillation flask, the ethanol and water boils and liquids may distil together • Vapours of liquids with higher boiling points condense along fractionating column and re-enter the round-bottomed flask • Ethanol distils over. In condenser, ethanol vapour condenses. • Ethanol is collect as distillate. 2 3 1 4

27. How does temperature change as solution of ethanol and water undergoes fractional distillation? Temperature (℃) • The temperature of mixture increases as it’s heated • At 78 ℃, ethanol distils over. The temperature remains constant until all ethanol has distilled out of round-bottomed flask • Temperature then increased until 100 ℃. At 100 ℃, water distils over. Temperature remains unchanged as water is being distilled.

28. Industrial applications of fractional distillation • Fractional distillation is used in industries to obtain nitrogen, argon, oxygen from air • Fractional distillation can be used to separate mixtures of liquids such as crude oil • Ethanol is formed when glucose solution undergoes fermentation in presence of yeast. • We can separate ethanol from glucose solution by fractional distillation