1. Separation and Purification Techniques

3. Soft Toys
Games
Books

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

5. 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.

6. To test for Purity of a Substance
Methods of Testing
Observation
Melting point
If a substance is pure, it will melt at a fixed temperature.
Boiling point
If a substance is pure, it will boils at a fixed temperature.
Use of chromatography
If a substance is pure, it will show only one spot on the chromatogram.

7. Effect of impurities in a substance
Attributes
Effect of impurities
Melting point
A substance melts below its melting point.
Boiling point
A substance boils higher than its boiling point.
Use of chromatography
Gives rise to more than one spot on the chromatogram.
Salt can be used to melt ice that freezes a car to the driveway by sprinkling a thin layer over the car and around the tires, and the salt will react chemically with the snow to melt it away.

8. 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.

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

10. Filtration
Solid-Liquid Mixture

11. 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

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

13. CRYSTALLISATION
Separating soluble solids from a solution

14. 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.

15. 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.

16. 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.

17. 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?

18. Simple Distillation
Separating liquid from a solution

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

20. 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.
Liquid is heated until its boiling point and changes to vapour. 1
Vapour is cooled and changes to liquid (distillate). 2
The vapour is cooled in the condenser until the temperature falls below the boiling point when it condenses back into a liquid which is collected in a container.
If the inlet is below the outlet then the water fills the entire volume of the condenser before getting to the outlet. If you set it up so the water inlet is above the outlet then the water will run down the side of the condenser and out again. This is all the work of gravity. The condenser will operate at it's most effective if it is completely full of water, this is because it works by heat transfer from the vapors in the condenser to the cool water in the condesner. Surface area to volume ratio is maximised in a full condenser and the larger the volume of water the more capacity for heat transfer, thus maximising cooling of the vapor.
Mixture
To ensure smooth boiling.
Other examples:
1. Marble chips
2. Porcelain chips

21. 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.
Never add a boiling chip to a hot solvent, because it can cause immediate boiling over of the solution. If you forget to add a boiling chip before you begin, you must cool the solution before adding one to prevent product loss. Boiling chips cannot be re-used since the pores inside these stones become filled with liquid on cooling.

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

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

24. Fractional Distillation
Separating miscible liquids

25. 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.

26. 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

27. 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.

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

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

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

31. Think!!!
What is the difference between distillation and fractional distillation?
Simple distillation
Fractional Distillation
No fractionating column
Has a fractionating column
Separate liquids whose boiling points differs more than 20°C
Able to separate liquids whose boiling point differs by less than 20°C

32. 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.

33. TYPES of MIXTURES MIXTURE SUBSTANCES TO OBTAIN METHODS
Salt mixed with broken glass pieces
Salt crystals
Evaporation
Sea Water
Pure Salt
Desalination/
Distillation
Copper (II) Sulphate solution
Copper (II) Sulphate Crystals
Crystallisation
Ink
Pure Water
Paper Chromatography
Wine
Ethanol
Fractional Distillation
get students to think back and confirm on the type of methods they can apply to use after the end of introducing the methods 33

34. 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

35. 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
Liquid
Boiling point (°C )
propanone 48
Ethanol 78
Water
100

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

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

38. Online Quiz
try/septechniques/septechniques1a.htm