Separating and Analysing

Page 1

SIMPLE DISTILLATION:

E.G. pure water from salt water

Substance boils and is condensed back again to liquid by condenser

Unwanted substance remains in flask

Whether to use simple or fractional depends on differences between boiling points of two substances. If large i.e. >70, then use simple.

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FRACTIONAL DISTILLATION:

Used to separate liquids completely miscible with each other E.G. alcohol and water

Can separate by using different boiling points

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SEPARATING FUNNEL:

Immiscible substances E.G. petrol and water

Petrol floats on top of water

Separating funnel to run them off in two different beakers

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FILTRATION:

One component can pass through but other is caught by it

E.G. rock salt - if crush and mix with hot water, salt dissolves but impurities don't

Salt solution (filtrate) drips through filter paper and can be heated to remove water

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RECRYSTALLISATION:

Purify soluble substances contaminated with small quantities of other soluble substances

Impure solid dissolved in minimum amount of hot water or other suitable solvent

Allowed to cool again

Most solids less soluble in cool than hot so crystals formed again

Impurities stay in solution

Crystals filtered and washed on filter paper with cold water or other solvent

Allowed to dry

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PAPER CHROMATOGRAPHY:

Example - spot of ink placed on chromatography paper

Paper hung in boiling tube containing some solvent

Solvent soaks up into paper

Paper in sealed tube stops solvent drom evaporating as travels up paper

Dyes that make up ink will differ in how strongly stick to paper and how soluble in solvent

Spot C barely moved so either not soluble in solvent or stuck firmly to paper or both

A moved almost as far as solvent so either very soluble or not attached to paper or both

Pattern you get = chromatogram

Ink minimum 3 different dyes but could be more

One of spots made up of two similar colour dyes that moved same distance - find by trying with different solvent

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COLLECTING AND IDENTIFYING GASES:

HYDROGEN:

Less dense than air so would go upwards

Almost insoluble in water

Over water or upwards into test tube or gas jar

Pops when lighted plaint held to mouth of tube

CARBON DIOXIDE:

Denser than air so would go downwards

Downwards into test tube or gas jar

Only slightly soluble in water so can be collected over water

Turns lime water milky or chalky

CHLORINE:

Denser than air

Downwards into test tube or gas jar

Too soluble to collect over water

Can collect over concentrated salt solution

Green gas - bleaches damp litmus paper

AMMONIA:

Less dense than air

Extremely soluble in water

Upwards into test tube or gas jar

Damp red litmus paper blue

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TESTING FOR WTAER:

ANHYDROUS COPPER (II) SULFATE:

Water turns anhydrous copper (II) sulphate blue

Anhydrous copper (II) sulfate lacks water of crystallisation and is white so when water added, replaces water of crystallisation, blue

COBALT CHLORIDE PAPER:

When dry, paper blue

Water turns it pink

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FLAME TESTS:

Shows presence of certain metal ions in compound

Platinum/nichrome wire cleaned y dipping into concentrated HCl

Lithium - red

Sodium - orange

Potassium - lilac

Calcium - brick-red

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OTHERS:

Copper (II) hydroxide --> blue precipitate

Iron (III) hydroxide --> orange-brown precipitate

Iron (II) hydroxide --> green precipitate

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TESTING FOR SULFATES:

Make solution of suspected sulphate in pure water

Add enough dilute HCl to make acidic

Add barium chloride solution

Sulfate will produce white precipitate of barium sulphate

Add HCl to destroy other compounds which could produce white precipitate E.G. if carbonate present as barium carbonate white and insoluble

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TESTING FOR CHLORIDES, BROMIDES, IODIDES:

Make solution of suspected chloride, bromide, iodide in pure water

Add enough dilute HNO3 to make it acidic

Add silver nitrate solution

Acid added to remove substances which could produce precipitates with silver nitrate solution

Chloride - white precipitate of silver chloride

Bromide - pale cream precipitate of silver bromide

Iodide - yellow precipitate of silver iodide