Study of Compounds- Sulphuric Acid-ICSE-Class 10|Biswajit Das

1. General Information and Introduction

• Formula and Molecular Mass: The chemical formula for sulfuric acid is H2​SO4​. Its molecular mass is approximately 98 g/mol.
• Nature: It is a colorless, oily, viscous liquid that is highly corrosive. It’s a strong dibasic acid, meaning it can furnish two hydrogen ions per molecule. The concentrated form has a strong affinity for water.
• Physical Properties: Sulfuric acid has a high boiling point (338∘C) and a high density. The process of diluting concentrated sulfuric acid is highly exothermic, so it is crucial to add the acid slowly to water, with constant stirring, and not the other way around.

2. Industrial Manufacturing: The Contact Process

The Contact Process is the main industrial method for producing sulfuric acid. It involves three key steps:

1. Production of Sulfur Dioxide (SO2​): Sulfur is burned in air to produce sulfur dioxide.S+O2​→SO2​
2. Catalytic Oxidation of Sulfur Dioxide: Sulfur dioxide is oxidized to sulfur trioxide (SO3​) in the presence of a catalyst, vanadium pentoxide (V2​O5​), at a temperature of around 450°C and a pressure of 1-2 atmospheres. This is a reversible and exothermic reaction.2SO2​+O2 = 2SO3​
3. Absorption of Sulfur Trioxide: Sulfur trioxide is dissolved in concentrated sulfuric acid to produce oleum (fuming sulfuric acid). This step is done to avoid the formation of a sulfuric acid mist that would be difficult to condense.SO3​+H2​SO4​→H2​S2​O7​Finally, oleum is diluted with water to obtain sulfuric acid of the desired concentration.H2​S2​O7​+H2​O→2H2​SO4​

3. Chemical Properties

As an Acid:

• Reaction with Metals: Dilute sulfuric acid reacts with active metals (above hydrogen in the reactivity series) to produce a salt and hydrogen gas.Zn+H2​SO4​ (dilute)→ZnSO4​+H2​
• Reaction with Bases: It neutralizes bases to form a salt and water.2NaOH+H2​SO4​→Na2​SO4​+2H2​O
• Reaction with Carbonates: It reacts with carbonates to produce a salt, water, and carbon dioxide.CaCO3​+H2​SO4​→CaSO4​↓+H2​O+CO2​

As a Non-Volatile Acid:

• Concentrated sulfuric acid can be used to prepare volatile acids like nitric acid or hydrochloric acid from their salts.NaCl+H2​SO4​→NaHSO4​+HCl

As an Oxidizing Agent:

• Hot, concentrated sulfuric acid acts as a strong oxidizing agent. It oxidizes metals and non-metals, and in the process, it gets reduced to sulfur dioxide.Cu+2H2​SO4​ (conc)→CuSO4​+2H2​O+SO2​C+2H2​SO4​ (conc)→CO2​+2H2​O+2SO2​

As a Dehydrating Agent:

• Concentrated sulfuric acid is a powerful dehydrating agent, meaning it removes water or the elements of water (H and O) from compounds.
• Dehydration of Sugar: When added to sugar, it removes water, leaving behind a black, porous mass of carbon.C12​H22​O11​H2​SO4​ (conc)​12C+11H2​O

4. Uses of Sulfuric Acid

Sulfuric acid is often called the “King of Chemicals” because of its wide range of applications.

• Fertilizers: Used in the production of fertilizers like ammonium sulfate and superphosphate.
• Chemicals: Used in the manufacture of other acids, plastics, synthetic fibers, and drugs.
• Metallurgy: Used in the cleaning of metals (pickling) before galvanizing or electroplating.
• Petroleum Refining: Used to purify kerosene and other petroleum products.
• Car Batteries: Dilute sulfuric acid is used as the electrolyte in lead-acid batteries.