Chapter 3: Separation TechniquesChapter 3: Separation Techniques

You will learn about:

• Pure substances

• Methods of purification:

- Chromatography

- Filtration

- Crystallization

- Distillation

You will learn about:

• Pure substances

• Methods of purification:

- Chromatography

- Filtration

- Crystallization

- Distillation

How do we know which are the real products?

Pure SubstancesPure Substances MixturesMixtures

Composition

A single substance not

mixed with anything else

Contains two or more substances

Melting and boiling points

Fixed pointsOver a range of

temperature

Chromatography

Produces a single spot on the

chromatography paper.

Contain two or more spots.

Testing for PurityTesting for Purity

A technique using a solvent to separate a mixture into its components.

E.g separate dyes in ink, detect traces of banned food substances, identify poisons or drugs.

A technique using a solvent to separate a mixture into its components.

E.g separate dyes in ink, detect traces of banned food substances, identify poisons or drugs.

(i) Chromatography(i) Chromatography

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1. Food colouring is applied to chromatography paper.

2. The paper is dipped into a solvent. (e.g water, alcohol)

3. The solvent travels up the paper, dissolving and carrying the dye along with it.

4. Coloured spots are seen in different positions on the paper at the end of results.

1. Food colouring is applied to chromatography paper.

2. The paper is dipped into a solvent. (e.g water, alcohol)

3. The solvent travels up the paper, dissolving and carrying the dye along with it.

4. Coloured spots are seen in different positions on the paper at the end of results.

Procedure: Procedure:

Culprit

Ben Johnson stripped from his Olympic goldin 1988.

ii) Filtration: separating a solid from liquid

1.1. A mixture is poured into the filter funnel A mixture is poured into the filter funnel lined with lined with filter paperfilter paper. .

2.2. Liquid particles are small enough to go Liquid particles are small enough to go through the pores of the filter paper but through the pores of the filter paper but the solid particles are too large to go the solid particles are too large to go through.through.

3.3. Collect the Collect the filtratefiltrate that passes through that passes through the filter paper in a conical flask. The the filter paper in a conical flask. The solid that remains in the filter paper is solid that remains in the filter paper is called called residueresidue..

1.1. A mixture is poured into the filter funnel A mixture is poured into the filter funnel lined with lined with filter paperfilter paper. .

2.2. Liquid particles are small enough to go Liquid particles are small enough to go through the pores of the filter paper but through the pores of the filter paper but the solid particles are too large to go the solid particles are too large to go through.through.

3.3. Collect the Collect the filtratefiltrate that passes through that passes through the filter paper in a conical flask. The the filter paper in a conical flask. The solid that remains in the filter paper is solid that remains in the filter paper is called called residueresidue..

iii) Evaporation to Dryness & Crystallisation

1. Pour some distilled water into the

mixture to dissolve the soluble

substance.

2. Filter the mixture.

3. Wash the residue with a little

distilled water to remove all the salt

solution from it. The residue is sand.

4. Evaporate the filtrate to dryness.

Salt is recovered.

Procedure:

iv) Distillation: separating a liquid from a solution

Procedure:1. Solution is heated in a flask until

the solution boils.2. Pure liquid turns into a vapour and

leaves the flask 3. Vapour is then cooled by a

condenser, which changes it back into a liquid

4. Liquid is called the distillate and is collected in a conical flask.

2. In the condenser, water vapour condenses.

1. In the distillation flask, water boils and enters the condenser.

How does simple distillation work?

3. Pure water is collected as distillate.

SAFETY MEASUREMENTS:

This ensures that the thermometer measures the boiling point of the substance that is being distilled.

Thermometer

Boiling Chips To ensure smooth boiling.

If the distillate is volatile, the receiver can be put in a large container filled with ice.

This helps to keep the temperature of the distillate low so that it remains in the liquid state.

Eg. Finding out the dyes present in sweets

Paper chromatography

• a method of a method of separating & separating & identifyingidentifying mixtures. mixtures.

• a suitable solvent is a suitable solvent is used.used.

Purity of SubstancesPurity of Substances• pure substances have pure substances have fixedfixed

melting and boiling pointsmelting and boiling points• melting pointsmelting points and and boiling boiling

pointspoints are changed by the are changed by the presence of impuritiespresence of impurities