Chapter 8 Salts (a)

Form 4 Chemistry Chapter 8 Salts (a)

Salts

1. A salt is an ionic compound that is formed when the hydrogen ion in an

acid is replaced by a metal ion or ammonium ion.

2. Salt is neutral, therefore the pH is 7.

3. Salt is neutral in terms of electrical charges

4. Salt can be produced from neutralisation reaction between acid and base

H2SO4 + CuO

HCl + KOH

HNO3 + Mg(OH)2

5. Example of salts from their corresponding acids

Acid General name of salt Examples of salts

Hydrochloric acid

Nitric acid

Sulphuric acid

Carbonic acid

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Soluble Salts and Insoluble Salts

1. Information on the solubility of salts is useful

a) The separation of salts in a salt mixture

b) Choosing the methods to prepare a salt

c) Identifying the types of ions in a salt in qualitative analysis of salts

2. The solubility of salt in water depends on the types of cations and anions

present as show below

Type of salt Solubility in water

Sodium, potassium and

ammonium salts

All are soluble

Nitrate salts All are soluble

Chloride salts

Sulphate salts

Carbonate, oxide and

hydroxide salts

3. Lead halides such as lead(II) chloride, lead(II) bromide and lead(II)

iodide are insoluble in cold water but soluble in hot water.

4. Filtration can be used to separate an insoluble salt from a soluble salts.

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Exercise

Determine whether the following salt is soluble or insoluble in water

Salt Solubility Salt Solubility

Magnesium

nitrate

Lead(II) oxide

Zinc chloride Ammonium

sulphate

Magnesium

sulphate

Iron (II) sulphate

Barium sulphate Aluminium

hydroxide

Aluminium

chloride

Copper (II)

hydroxide

Lead (II) nitrate Potassium

chloride

Zinc oxide Magnesium

chloride

Barium iodide Zinc sulphate

Silver chloride Sodium nitrate

Ammonium

chloride

Potassium nitrate

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Preparation of Soluble Salt

1. Soluble salt can be produced through four types of reaction:

a)

b)

c)

d)

Exercise

Suggest two methods (if any) to prepare the follow salts. Write the

chemical equation.

1. Sodium chloride

2. Potassium nitrate

3. Ammonium sulphate

4. Zinc sulphate

5. Zinc chloride

6. Magnesium chloride

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7. Copper(II) sulphate

Question: Copper (II) chloride cannot be prepared by adding copper metal

to hydrochloric acid. Explain. Then, suggest another way to prepare copper

(II) chloride. (3 marks)

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SPM Essay Question

Preparation of soluble copper(II) sulphate salt using acid and oxide metal.

(10 marks)

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50cm3 of 1.0 mol dm-3 sulphuric acid is added into a beaker and is

____________.

________________ powder is added into the hot sulphuric acid

while continuously stirring with a glass rod.

Copper(II) oxide powder is added and stirred

until_____________________________.

The mixture is ______________ to remove excess copper(II) oxide.

The filtrate is _____________ to about half of its original volume.

The saturated solution is cooled in room temperature for

crystallisation to occur.

Blue crystals formed are removed by filtration and rinsed with

distilled water.

Then, the crystalized salt is dried between filter paper.

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Question

1. Why copper(II) oxide powder is used and not copper (II) oxide chips?

2. Why excess copper (II) oxide powder is used?

3. Why the filtrate is not heated until it is dry to produce copper (II) sulphate salt?

4. How do we know all the acid has reacted completely?

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Preparation of Insoluble Salt

1. Insoluble salt exist as precipitate

2. Insoluble salt is prepared by double decomposition or precipitation by

mixing two soluble salt solutions.

3. This method requires two aqueous solutions

4. One of the solutions contains the required position ions while another

solution contains the required negative ions.

5. Example, lead(II) iodide salt can be prepared through the reaction

between lead(II) nitrate and potassium iodide

Chemical equation:

Ionic equation:

ExercisesComplete the following table

Insoluble salt Required Solution

Silver chloride

Lead (II) iodide

Calcium carbonate

Lead (II) sulphate

Barium sulphate

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Write the chemical and ionic equations for the following double

decomposition reaction below:

a) Lead(II) nitrate and sodium sulphate

b) Calcium chloride and sodium carbonate

c) Barium chloride and sodium sulphate

d) Silver nitrate and potassium chromate (VI)

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Preparation of Insoluble Barium Sulphate

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25cm3 of ________________ is added to 25cm3 of __________________

solution in a beaker

The mixture is stirred with a ___________________.

A white precipitate is formed immediately.

The mixture is __________________ to obtain the white solid of

_____________________ as residue.

The residue is ________________ to remove any traces of other ions in

it.

Then, it is rinsed with distilled water and dried by pressing between two

pieces of ___________________.

Chemical equation:

Ionic Equation:

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Chapter 8 Salts (a)

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