Separation and Purification Techniques
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Transcript of Separation and Purification Techniques
Separation and Separation and Purification TechniquesPurification Techniques
Soft Toys Games Books
But what if…
Sand
Sugar
How to separate them?
Lesson ObjectivesLesson ObjectivesAt 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.
To test for Purity of a To test for Purity of a SubstanceSubstance
Methods of Testing
Observation
Melting pointIf a substance is pure, it
will melt at a fixed temperature.
Boiling pointIf 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.
Effect of impurities in a Effect of impurities in a substancesubstance
Attributes Effect of impurities
Melting pointA substance melts below
its melting point.
Boiling pointA substance boils higher
than its boiling point.
Use of chromatography
Gives rise to more than one spot on the chromatogram.
Physical Methods of Physical Methods of SeparationSeparationOnly separate the different
substances in a mixture. No new substance is formed.
The choice of separation technique depends on the nature of the mixture.
Common physical methods to Common physical methods to separate a mixtureseparate a mixture
◦Paper chromatography◦Filtration◦Crystallisation ◦Simple and fractional distillation
FILTRATIONFILTRATION
Solid-Liquid Mixture
FiltrationFiltrationSolid-liquid mixture (insoluble solids)
E.g. sand in waterA filter paper is used because it
contains very tiny pores.
Mixture of solid
and liquid
Applications Applications NEWater – purification of water
using microfiltration to remove impurities.
CRYSTALLISATIONCRYSTALLISATION
Separating soluble solids from a solution
Crystallisation To separate dissolved pure solid from a solution.
1. Heat the solution until saturated.
3. Pure Crystals formed.
Evaporation of solution
2. Saturated solution
Maximum amount of solid dissolved in a given solvent.
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.
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.
Mixture of Sand and SugarHow 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?
SIMPLE DISTILLATIONSIMPLE DISTILLATION
Separating liquid from a solution
DistillationDistillationTo separate a liquid from a
solution. E.g. salt solution, sugar solution
Involves two physical state changes.
Set-up for distillationSet-up for distillation
Liquid is heated until its boiling point and changes to vapour.
1
Mixture
Vapour is cooled and changes to liquid (distillate).
2
Main conceptBoiling point of the liquid
To ensure smooth boiling.
Other examples:
1. Marble chips 2. Porcelain chips
Bulb of thermometer placed beside the side arm of the distillation flask to ensure accurate measurement of boiling point.
Boiling chipsBoiling chipsTo ensure smooth boilingDuring boiling of water, big air
bubbles can be seen. These air bubbles causes
‘bumping’.Boiling chips can reduce this
‘bumping’ effect.
Temperature Profile Temperature Profile
Temperature as solution is heated
Temperature remains unchanged until all the liquid boils off.
Disadvantage of Simple DistillationUnable to separate liquids who
boiling point differ by less than 20°C.
Use fractional distillation!
FRACTIONAL FRACTIONAL DISTILLATIONDISTILLATION
Separating miscible liquids
Fractional distillationFractional distillationFor 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.
Set-up of fractional Set-up of fractional distillationdistillation
Round-bottomed flask
Fractionating column
Thermometer
Liquid-liquid mixture
Boiling chips
Condenser
Distillate
Water inlet
Water outlet
Main conceptBoiling point of the liquids where the liquid with the lowest boiling point will distill over first.
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.
Fractionating ColumnFractionating Column
Packed with glass beads Provide large surface area for
evaporation and condensation of liquids with different boiling points for effectively separation.
Temperature ProfileTemperature Profile
First liquid distill over upon reaching its boiling point
Liquid with lowest boiling point will distill over first
Second liquid distill over.
Industrial Applications Industrial Applications Separation of liquid airSeparation of crude oilSeparation of alcohol from
fermented solution.
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
Think!!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.
TYPES of MIXTURESTYPES of MIXTURESMIXTURE SUBSTANCES
TO OBTAINMETHODS
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
Check your UnderstandingCheck your UnderstandingWhich 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
Check your UnderstandingCheck 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 48Ethanol 78Water 100
What did you learnt What did you learnt today?today?3 methods to test for purityEffect of impurities in a
substance3 separation techniques and their
working principles
SummarySummarySimple distillationFractional 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
Online QuizOnline Quiz
http://www.sciencequiz.net/jcscience/jcchemistry/
septechniques/septechniques1a.htm