Chem Notes Sep Tech

1 Methods of Purification 1) Common apparatus used:

Burette

Bunsen Burner

Pipette

Separating Funnel

Measuring Cylinder

Beaker

Filter funnel

Heating Tube

Liebig Condenser (Distillation)

Crucible

Beaker

Beaker

Copyright: Stephanie Teo Diagrams from Chemistry For O Level By JGR Briggs (Longman Publishers) Unless otherwise stated

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Apparatus for collecting Gases (Refer to Notes on Speed of Reactions)

Apparatus for finding boiling point

Apparatus used in Titration Copyright: Stephanie Teo Diagrams from Chemistry For O Level By JGR Briggs (Longman Publishers) Unless otherwise stated

3 2) Burette -used in titration (refer to notes on Acids, Bases and Salts) -measure volumes of liquid accurate up to 0.1 cm3 ** Measuring cylinder and beaker can only measure accurate up to 1 cm3 Pipette – also used in titration (refer to notes on Acids, Bases and Salts) – measures fixed volumes of 25.0 cm3 or 50.0 cm3 3) Pure substance boils at fixed melting point and boiling point at a given pressure. Impurities will lower melting point and raise boiling point A mixture boils over a range of temperatures. Purity of substances is important especially in foodstuffs and drugs. Any impurity in these substances can kill. Purification needs to be carried out. Pure silicon is used to make silicon chips for making microprocessors Pure copper is needed to make copper wires used in electrical wiring. Different gases are collected using different methods:

Collect insoluble gas

Collect gas lighter than air

4) Summary of separation techniques: Separation Technique

Collect gas heavier than air

Purpose Obtain a solute from solution (Solute cannot be decomposed by heat)

Example Sodium chloride from sodium chloride solution

Evaporation

Copyright: Stephanie Teo Diagrams from Chemistry For O Level By JGR Briggs (Longman Publishers) Unless otherwise stated

4 Evaporation to dryness Separate solid from liquid

Sand from water Calcium carbonate from water

Separate immiscible liquids (liquids which do not mix)

Oil and water Paraffin and water Benzene and water

To dry a gas

** Common drying agent is concentrated sulphuric acid

Filtration

Separating funnel

Copyright: Stephanie Teo Diagrams from Chemistry For O Level By JGR Briggs (Longman Publishers) Unless otherwise stated

5 Drying a gas Obtain a Water from solvent from a seawater solution

Distillation Separate miscible liquids with different boiling points

Ethanol and water Crude oil Liquid air Fermented liquor

Separate small amounts of substances which are soluble in the named solvent

Dye and Inks (Compare with a known substance)

Fractional Distillation

Mixture of amino acids (compare Rf values)

Copyright: Stephanie Teo Diagrams from Chemistry For O Level By JGR Briggs (Longman Publishers) Unless otherwise stated

6 Chromatography

Results of chromatography Dissolving and filtering **Dissolving = Dissolution

Crystallisation **Can purer crystals

Magnetism

Sublimation

To separate soluble substance from insoluble substance Obtain crystals from saturated salt solution

Separate magnetic substance (mainly iron) from a nonmagnetic substance Separate a substance that can sublime from one that cannot

Sodium chloride (soluble) from sand Sugar (soluble) from sand Copper(II) sulphate crystals from copper(II) sulphate solution Sodium chloride crystals from sodium chloride solution Iron filings from sulphur

Ammonium chloride from sodium chloride Iodine from copper Napthalene (moth ball)

Copyright: Stephanie Teo Diagrams from Chemistry For O Level By JGR Briggs (Longman Publishers) Unless otherwise stated

7 from sand Chromatography -can identify substance -determine purity of substance -separate two or more substances in a mixture -substances must be soluble in same solvent -Common solvents: water , ethanol -Most soluble substance will travel furthest up the chromatogram

Example of paper chromatography set-up

Possible chromatograms obtained -Pure substance will only produce one spot on the chromatogram -Impure substance will produce more than one impure substance on the chromatogram

Copyright: Stephanie Teo Diagrams from Chemistry For O Level By JGR Briggs (Longman Publishers) Unless otherwise stated

8

Steps in Paper Chromatography (adapted from Effective Guide to ‘O’ Level Chemistry by Longman Publishers):

Copyright: Stephanie Teo Diagrams from Chemistry For O Level By JGR Briggs (Longman Publishers) Unless otherwise stated

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Rf value = Distance travelled by component / Distance travelled by solvent Different substance has different Rf value. Chromatography can be used to separate and identify colourless substances -Chromatogram is sprayed with a locating agent to show where the substances are on the paper -Locating agent is a chemical that reacts with the substances to produce a coloured product

Copyright: Stephanie Teo Diagrams from Chemistry For O Level By JGR Briggs (Longman Publishers) Unless otherwise stated