C2 Topic One - Qualitative Analysis

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Analysing Substances + Tests for Ions

Chemical analysis is useful e.g. blood tests - for monitoring general health and diagnosing diseases, also alcohol content of blood. Water companies - purity of the drinking water they provide.

Qualitative analysis tells you what is present (even a trace can be bad)

Quantitative analysis tells you how much is present

Test for Positive Ions using NaOH to give a coloured metal hydroxide precipitate

Add a few drops of NaOH to your solution to form a coloured insoluble hydroxide hopefully!

Calcium - White Copper(II) - Blue Iron (II) - Green Iron (III) - Brown

Aluminium - White. But then dissolves in excess NaOH to become colourless.

Ammonium - No precipate, but gives off amonia when heated. Amonia - damp universal indicator paper goes purple, red litmus paper goes blue, also smell: urine.

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More Tests for Ions

Test for halides with dilute nitric acid then silver nitrate

Acid gets rid of carbonate ions before test.      Iodide - yellow precipitate silver iodide.

Chloride - white precipitate silver chloride.     Bromide - cream precipitate silver bromide.

Flame Tests

Sodium - yellow/orange  Potassium - lilac Calcium - brick red Copper - blue/green

Test for carbonates - any carbon dioxide?

Carbonate+acid=CO2 -bubble through limewater -milky? Then CO2 -was a carbonate.

Test for sulphates with dilute hydrochloric acid then barium chloride solution

If white precipitate of barium sulphate is formed then original compound was a sulphate.

Test for chlorides with dilute nitric acid then silver nitrate solution

If white precipitate of silver chloride is formed then original compound was a chloride.

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