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

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