The document discusses various separation techniques used to separate mixtures into their pure constituents. It describes techniques such as filtration, distillation, evaporation to dryness, chromatography, magnetic separation, crystallization, and separating immiscible liquids. Fractional distillation and crystallization are highlighted as key processes for separating mixtures into their pure components. The document provides detailed explanations of the procedures and applications of several important separation methods.

1. Separation Techniques
LSS 1 Term 3

2. Mixtures and Pure Substances
• Recap: How do we define mixture?
• A mixture contains two or more constituent
substances which are not chemically
combined together.
• A mixture retains the properties of its
constituents.
• Examples include: air, seawater, alloys like
brass, bronze and steel

3. Is water a mixture?
• Water from sea?
– Mixture of sand, salt, dead matter, etc.
• Water from tap?
– Solution of small amounts of minerals
– Click here to find out what’s in our tap water.
• Deionized water?
– Purified water formed by removing ions
present in water source
– Click here to find out more.

4. Pure substances
• Pure substance is a single substance not
mixed with anything else.
• Most things around us are not pure
substances.
• Eg. Gold used in jewellery
• Purification processes need to be used to
obtain pure substances.

5. Separation Techniques
• Separation techniques refers to the
physical methods that can be used to
separate the constituents of mixtures.
• Sometimes, a combination of separation
techniques will be used to obtain pure
substances.
• Separation techniques are essentially
methods of purification.

6. Separation Techniques
• Filtration
• Evaporation (to dryness)
• Distillation (Simple and Fractional)
• Chromatography
• Magnetic Attraction/ Separation
• Crystallization
• Separating immiscible liquids

7. Discussion
• With the help of diagrams, describe the
following separation techniques and the
kind of mixture (solid-solid, solid-liquid,
etc.) it can be used to separate:
– Filtration
– Distillation
– Evaporation to dryness

8. Separating Immiscible Liquids
• ‘Miscibility’ describes how well two
substances mix together.
• Two liquids are immiscible if they do not
mix with each other.
• This will give a two-layered liquid mixture.
• Question: Which liquid will be on top of the
other?
• Example: Oil and water

9. • To separate two immiscible liquids, a
separating funnel is used.
Separating Immiscible Liquids

10. Separating Immiscible Liquids
Separating Petrol from Water
• Immiscible liquid mixture is poured
into separating funnel.
• Allow some time for the liquid
mixture to settle and form two
distinct layers.
• Open tap to allow the lower water
layer to run out into a beaker.
• The tap is closed as the last drop of
water runs out.
• The tap is then opened to allow
petrol to run out into another beaker.

11. Limitations of Evaporation to
Dryness as a purification method
• Many substances decompose when
heated strongly.
– Eg. Sugar decompose to give water and
carbon (black substance) on heating strongly.
• Most crystals give off water to become
powders when heated.
• Soluble impurities are left behind with the
crystal/powder form of the substance
when water is evaporated off.

12. Crystallization
• The best method for separating a pure
solid sample from its solution, i.e. to obtain
pure crystals of the solute from the
solution it is dissolved in.

13. Procedure of Crystallization
• Heat solution until most of the solvent has
evaporated off. A hot saturated solution is
obtained.
• Allow saturated solution to cool. On
cooling, solute appears as pure crystals
while impurities stay in the solution.
• Filter and Dry crystals by pressing it
between pieces of filter paper.

14. Procedure of Crystallization

15. Applications of Crystallization
• Used to purify crystals and substances
that decompose on strong heating
• Industrial Application:
– Used in production of silicon wafers for
microchips (the Czochralski Method)
– Extraction of pure chemicals like sodium
chloride and potassium chloride from the
mixture of dissolved chemicals from Dead
Sea using fractional crystallization.

16. Magnetic Attraction
• Magnets can be used to separate a
magnetic metals from a mixture of solids.
• Examples of magnetic metals: iron, nickel,
cobalt. Steel is a magnetic alloy containing
iron.
• Method widely used in removal of
magnetic materials from domestic waste
for recycling.

17. Further Applications of Magnetic
Attraction
• Magnetic
Filters to
remove
metallic
particles from
lubricating oil
in cars and
machineries

18. Simple vs Fractional Distillation
• Simple distillation is used to separate
solvent from a non-volatile solute (i.e.
solute with high boiling point). Eg. Water
from salt solution.
• Fractional distillation is used to separate
mixture of miscible liquids, eg. Mixture of
ethanol and water.

19. Fractional Distillation

20. How fractionating column works
• May be filled with glass beads, plates or a spiral.
• These provide a large surface area for vapour to
condense on.
• Liquid with lowest boiling point will distill over to
the condenser first
• Vapours of liquids with higher boiling points
condense along fractionating column and re-
enters the round-bottomed flask

21. How ethanol makes its way to
condenser ahead of water
• Animation
• Bp of ethanol = 78oC, Bp of water = 100oC
• Vapour from boiling mixture contains larger
percentage of lower boiling point ethanol.
• As vapour mixture moves up fractionating
column, it repeatedly condenses and evaporates
inside the column.
• Each time the mixture evaporates, percentage of
lower boiling point ethanol increases.

22. How ethanol makes its way to
condenser ahead of water
• By the time vapour reaches top of
fractionating column, it has become almost
pure ethanol
• This vapour then passes into the
condenser where it is cooled, and
condenses into liquid ethanol.
• Thermometer will show temperature of
78oC until all ethanol has distilled off.

23. Chromatography

24. Chromatography procedure
• http://www.sambal.co.uk/chromatography.
html