ICSE Class 10 Chemistry Chapter 11 Sulphuric Acid

Sulphuric Acid

Syllabus

Sulphuric Acid - Its behaviour as an acid when dilute. As an oxidizing agent when concentrated - oxidation of carbon and sulphur; as a dehydrating agent - dehydration of sugar and copper (II) sulphate crystals; its non-volatile nature. Manufacture by Contact process (reference only). Detail of the process to be avoided.

Its behaviour as an acid when dilute - reaction with metal, metal oxide, metal hydroxide, metal carbonate, metal bicarbonate, metal sulphite, metal sulphide.

Concentrated sulphuric acid as an oxidizing agent - the oxidation of carbon and sulphur.

Concentrated sulphuric acid as a dehydrating agent - (a) the dehydration of sugar (b) Copper (II) sulphate crystals.

Non-volatile nature of sulphuric acid - reaction with sodium or potassium chloride and sodium or potassium nitrate.

Sulphuric Acid

Molecular formula: \(\text{H}_2\text{SO}_4\)

Relative molecular mass: 98

Structure: \[\text{H} - \text{O} - \text{S} - \text{O} - \text{H}\] with oxygen double bonded above and below the sulfur

Introduction

Sulphuric acid is rightly called the 'King of Chemicals' because there is no other manufactured compound which is used by such a large number of key industries. It has been known for a long time.

In the later Middle Ages, it was obtained as an oily viscous liquid by heating crystals of green vitriol, and was, therefore, known by the name of oil of vitriol.

\[2\text{FeSO}_4 \cdot 7\text{H}_2\text{O} \xrightarrow{\Delta} \text{Fe}_2\text{O}_3 + \text{SO}_2 + \text{SO}_3 + 14\text{H}_2\text{O}\]

The sulphur trioxide evolved gets dissolved in water forming sulphuric acid.

\[\text{SO}_3 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_4\]

Occurrence

In the free state, it is found in certain mineral springs and is formed by the action of water on certain sulphides.

In the combined state, as Barytes \(\text{BaSO}_4\), Gypsum \(\text{CaSO}_4 \cdot 2\text{H}_2\text{O}\) and Kiesterite \(\text{MgSO}_4 \cdot \text{H}_2\text{O}\), etc.

Preparation Of Sulphuric Acid

By Oxidation Of An Aqueous Solution Of Sulphur Dioxide With Oxygen, Chlorine Or Bromine

\[2\text{SO}_2 + 2\text{H}_2\text{O} + \text{O}_2 \rightarrow 2\text{H}_2\text{SO}_4\]

\[\text{SO}_2 + 2\text{H}_2\text{O} + \text{Cl}_2 \rightarrow \text{H}_2\text{SO}_4 + 2\text{HCl}\]

\[\text{SO}_2 + 2\text{H}_2\text{O} + \text{Br}_2 \rightarrow \text{H}_2\text{SO}_4 + 2\text{HBr}\]

The colour of \(\text{Cl}_2\) and \(\text{Br}_2\) fades.

Sulphur With Concentrated Nitric Acid

\[\text{S} + 6\text{HNO}_3 \rightarrow \text{H}_2\text{SO}_4 + 6\text{NO}_2 + 2\text{H}_2\text{O}\]

By Dissolving Sulphuryl Chloride In Water

\[\text{SO}_2\text{Cl}_2 + 2\text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_4 + 2\text{HCl}\]

Manufacture Of Sulphuric Acid (Contact Process)

The various steps in the Contact process are as follows:

Production Of Sulphur Dioxide

Sulphur dioxide is produced by roasting metallic sulphides in air

\[4\text{FeS}_2 \text{ (Iron pyrites)} + 11\text{O}_2 \rightarrow 2\text{Fe}_2\text{O}_3 + 8\text{SO}_2\]

OR

by burning Louisiana sulphur (99.5% pure) in purified air.

\[\text{S} + \text{O}_2 \rightarrow \text{SO}_2\]

Purification Of Gases

The mixture of sulphur dioxide and air contains various impurities which must be removed, otherwise the catalyst loses its efficiency.

Teacher's Note

Just as purifying air in a water filter removes particles, purifying gases in industrial processes removes impurities that would harm the chemical reactions - a principle similar to cleaning your room before guests arrive.

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