Download Chemistry Form 4 Chapter 8 PDF

TitleChemistry Form 4 Chapter 8
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Page 1

© MHS 2009 1

Chapter 8: Salts


- A salt is an ionic compound.

- The anion part comes from the acid while the cation part comes from a base.

- Example: KCl, KOH(aq) + HCl(aq)  KCl(aq) + H2O(l)

- A salt is a compound formed when the hydrogen ion. H+ from an acid is replaced by a metal ion

or an ammonium ion, NH4+.

Salts Soluble Insoluble

Nitrate salts - All nitrate salts -

Carbonate salts - Potassium carbonate, K2CO3

- Ammonium carbonate, (NH4)2CO3

- Sodium carbonate, Na2CO3

- All other carbonate salts

Chloride salts - All chloride salts

Except 

- Lead (II) chloride, PbCl2

- Silver chloride, AgCl

- Mercury Chloride, HgCl


Sulphate salts - All sulphate salts

Except 

- Lead (II) sulphate, PbSO4

- Barium sulphate, BaSO4

- Cacium sulphate, CaSO4

2. Preparation and purification of soluble salts

- The salts formed during preparation of soluble salts contain impurities.

- These salts need to be purified through a process known as recrystallisation.

- Physical characteristics of crystals:

i. Crystals have fixed geometrical shapes such as a cuboid, rhombic or prism.

ii. Crystals of the same substance have same shapes but may be in different sizes.

iii. Crystals have flat surfaces, straight edges and sharp angles.

iv. Crystals have fixed angles between two neighboring surfaces.

Example 1: Preparation of Soluble Salts  Na2SO4




Page 5

© MHS 2009 5

Flow Chart for selection of test for gas

8. Test For Anions


1 Carbonate ion,


- Pour 3 cm3 of aqueous carbonate solution into a test tube

- Add 2 cm3 hydrochloric acid, HCl

- Bubble the gas produced through limewater

- Lime water turned milky.

2 Chloride ion,


- Pour about 2 cm3 of aqueous chloride solution into test tube

- Add 2 cm3 nitric acid, HNO3

- Add 2 cm3 of silver nitrate solution, AgNO3.

- A white precipitate is formed with silver nitrate solution

3. Sulphate ion,


- Pour 2 cm3 of aqueous sulphate solution into test tube
- Add 2 cm3 hydrochloric acid, HCl
- Add 2 cm3 of barium chloride solution, BaCl2.
- A white precipitate is formed with barium chloride solution

4. Nitrate ion,


- Pour about 2 cm3 of aqueous nitrate solution into test tube

- Add 2 cm3 sulphuric acid, H2SO4.

- Add 2 cm3 of iron (II) sukphate, FeSO4 solution. Shake to mix well.

- Slant the test tube and add slowly concentrated sulphuric acid, H2SO4 down the

side of the test tube. Do not shake the test tube.

- A brown ring is formed.

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