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Separation and Purification Techniques

Separation and Purification Techniques. Soft Toys. Games. Books. But what if…. Sugar. Sand. How to separate them?. Lesson Objectives. At the end of the lesson, students should be able to: Name the 3 methods in which we can test for pure substances

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Separation and Purification Techniques

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  1. Separation and Purification Techniques

  2. Soft Toys Games Books

  3. But what if… Sugar Sand How to separate them?

  4. Lesson Objectives At the end of the lesson, students should be able to: • Name the 3 methods in which we can test for pure substances • Identify the effect of impurities on a substance. • Choose suitable separation techniques to separate a given mixture. • Explain the working principles behind each separation technique.

  5. To test for Purity of a Substance

  6. Effect of impurities in a substance

  7. Physical Methods of Separation • Only separate the different substances in a mixture. • No new substance is formed. The choice of separation technique depends on the nature of the mixture.

  8. Common physical methods to separate a mixture • Paper chromatography • Filtration • Crystallisation • Simple and fractional distillation

  9. Solid-Liquid Mixture Filtration

  10. Filtration • Solid-liquid mixture (insoluble solids) E.g. sand in water A filter paper is used because it contains very tiny pores. Mixture of solid and liquid

  11. Applications • NEWater – purification of water using microfiltration to remove impurities.

  12. CRYSTALLISATION Separating soluble solids from a solution

  13. Crystallisation • To separate dissolved pure solid from a solution. Maximum amount of solid dissolved in a given solvent. 2. Saturated solution Evaporation of solution 3. Pure Crystals formed. 1. Heat the solution until saturated.

  14. How to test for saturated solution? • Dip a glass rod into the solution and removed. • If crystals are formed on the glass rod, it means that the solution is saturated. • This is the saturation point or crystallisation point.

  15. Think!!! • Why can’t we just evaporate the solution to dryness to obtain the crystals? • For some substances, they will decompose when heated.  charring • When water is removed, any soluble impurities will be left on the crystal  not pure.

  16. Mixture of Sand and Sugar • How do I get sand and sugar back? • Filtration  Sand is the residue, filtrate is the sugar solution • Crystallisation  pure sugar crystals • Is the filtrate always a pure liquid?

  17. Separating liquid from a solution Simple Distillation

  18. Distillation • To separate a liquid from a solution. E.g. salt solution, sugar solution • Involves two physical state changes.

  19. Set-up for distillation Main concept Boiling point of the liquid Bulb of thermometer placed beside the side arm of the distillation flask to ensure accurate measurement of boiling point. 1 Liquid is heated until its boiling point and changes to vapour. 2 Vapour is cooled and changes to liquid (distillate). Mixture To ensure smooth boiling. Other examples: 1. Marble chips 2. Porcelain chips

  20. Boiling chips • To ensure smooth boiling • During boiling of water, big air bubbles can be seen. • These air bubbles causes ‘bumping’. • Boiling chips can reduce this ‘bumping’ effect.

  21. Temperature as solution is heated Temperature Profile Temperature remains unchanged until all the liquid boils off.

  22. Disadvantage of Simple Distillation • Unable to separate liquids who boiling point differ by less than 20°C. Use fractional distillation!

  23. Separating miscible liquids Fractional Distillation

  24. Fractional distillation • For liquids that are miscible and having different boiling points. • Miscible – mix together completely to form a solution. E.g. water and ethanol • Liquid with lower boiling point distill over first. • Liquids with higher boiling point will return back into the round-bottomed flask.

  25. Set-up of fractional distillation Main concept Boiling point of the liquids where the liquid with the lowest boiling point will distill over first. Water outlet Thermometer Condenser Fractionating column Round-bottomed flask Water inlet Liquid-liquid mixture Distillate Boiling chips

  26. During fractional distillation, • The liquid with lowest boiling point will distill over to the condenser first. • The vapour of liquids with higher boiling point condenses along the fractionating column and re-enter the round-bottomed flask.

  27. Fractionating Column • Packed with glass beads • Provide large surface area for evaporation and condensation of liquids with different boiling points  for effectively separation.

  28. Temperature Profile Liquid with lowest boiling point will distill over first Second liquid distill over. First liquid distill over upon reaching its boiling point

  29. Industrial Applications • Separation of liquid air • Separation of crude oil • Separation of alcohol from fermented solution.

  30. Think!!! • What is the difference between distillation and fractional distillation?

  31. Think!! • Is it possible to obtain salt from seawater? Yes • However, industrially, we use reverse osmosis to obtain salt (Desalination). What is the reason? Distillation exhaust a lot of energy, resulting in high production cost.

  32. TYPES of MIXTURES

  33. Check your Understanding Which process is used to separate • Three water-soluble dyes? • Two miscible liquids with boiling points of 78°C and 100°C? • Water containing an insoluble solid? • Water containing a dissolved solid? Chromatography Fractional distillation Filtration Crystallisation

  34. Check your Understanding • A mixture contains the following three liquids that are completely miscible: • The liquid can be separated by fractional distillation. State, with a reason, which liquid will distill over first. Propanone. It has the lowest boiling point among the 3 liquids. • Name an industrial process that involves fractional distillation. Fractional distillation of crude oil

  35. What did you learnt today? • 3 methods to test for purity • Effect of impurities in a substance • 3 separation techniques and their working principles

  36. Fractional distillation Simple distillation To separate miscible liquids To separate solvent from solution Separation technique To separate solid from a liquid To separate solid from a solution Filtration To separate solids (only one is soluble in a solvent) Crystallisation Summary

  37. Online Quiz http://www.sciencequiz.net/jcscience/jcchemistry/septechniques/septechniques1a.htm

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