Analytical Chemistry

1. Sir. Muhammad Abdul Mageid
CIE - IGCSE Chemistry
Chapter 8 Acids, Bases and Salts
8.4- Identification of Ions and Gases

2. Contents
8.2 Types of Oxides
8.1 The Characteristic Properties of Acids and Bases
8.4 Identification of Ions and Gases
8.3 Preparation of Salts
Tuesday, August 4, 2020
Sir. Muhammad Abdul Mageid

3. Tuesday, August 4, 2020
8.4 Identification of Ions and Gases
Sir. Muhammad Abdul Mageid
Test for aqueous cations
 Metal cations in aqueous solution can be identified by the colour
of the precipitate they form on addition of sodium hydroxide and
ammonia solution.
 If only a small amount of NaOH is used then normally the metal
hydroxide precipitates.
 In excess NaOH some of the precipitates may dissolve.
 A few drops of NaOH is added at first and any colour changes
or precipitates formed are noted.
 Then the NaOH is added in excess and the reaction is observed again.
 The steps are repeated for the test using ammonia solution.

4. Tuesday, August 4, 2020
8.4 Identification of Ions and Gases
Analysing results
 The table below contains the results for each of the cations included in the
syllabus.
 If a precipitate is formed from either NaOH or aqueous ammonia then the
hydroxide is insoluble in water.
 Zinc for example reacts as such: ZnCl2 (aq) + 2NaOH(aq) →Zn(OH)2 (s) + H2O (l)
 Ca2+ ions can be distinguished from Zn2+ and Al3+ as Ca(OH)2 calcium
hydroxide precipitate does not dissolve in excess NaOH but both zinc hydroxide
and aluminium hydroxide do.
 Zn2+ ions can be distinguished from Al3+ ions as Zn(OH)2 dissolves in excess
aqueous ammonia but Al(OH)3 does not.
 Most transition metals produce hydroxides with distinctive colours.
Sir. Muhammad Abdul Mageid

5. Tuesday, August 4, 2020
8.4 Identification of Ions and Gases
Test for aqueous cations
Sir. Muhammad Abdul Mageid

6. Tuesday, August 4, 2020
8.4 Identification of Ions and Gases
Tests for aqueous cations
 The flame test
is used to identify the metal cations by the colour of the flame they produce.
 A small sample of the compound is placed on an unreactive metal wire such as
nichrome or platinum.
 The colour of the flame is observed and used to identify the metal.
Sir. Muhammad Abdul Mageid

7. Tuesday, August 4, 2020
8.4 Identification of Ions and Gases
The different coloured flames produced by metal cations during flame tests
Sir. Muhammad Abdul Mageid

8. Tuesday, August 4, 2020
8.4 Identification of Ions and Gases
Tests for anions
Sir. Muhammad Abdul Mageid

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8.4 Identification of Ions and Gases
Tests for anions
Sir. Muhammad Abdul Mageid

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8.4 Identification of Ions and Gases
Tests for gases
Sir. Muhammad Abdul Mageid

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8.4 Identification of Ions and Gases
Tests for gases
Sir. Muhammad Abdul Mageid

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8.4 Past Papers Questions
Sir. Muhammad Abdul Mageid

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8.4 Past Papers Questions
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8.4 Past Papers Questions
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8.4 Past Papers Questions
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8.4 Past Papers Questions
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8.4 Past Papers Questions
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8.4 Past Papers Questions
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8.4 Past Papers Questions
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8.4 Past Papers Questions
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8.4 Past Papers Questions
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8.4 Past Papers Questions
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8.4 Past Papers Questions
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8.4 Past Papers Questions
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8.4 Past Papers Questions
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white (1)
precipitate (1)
with excess dissolves/colourless (1)

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8.4 Past Papers Questions
Sir. Muhammad Abdul Mageid
white precipitate (1)
insoluble/no change
(in excess) (1)

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8.4 Past Papers Questions
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contains water/hydrated
ammonia (1) not ammonium
nitrate (1) hydrated salt (1) not sulfate

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Sodium(1) bromide(1)
green

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green; (1)
precipitate;(1)
with excess, green solution / clear /
dissolves; (1)

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grey-green; (1) precipitate;(1)
white precipitate;
fume cupboard / protective clothing, e.g. gloves or goggles;(1)