What is the first step involved in forming sulphuric acid through contact process?

Burning of Sulphur or roasting sulphide ores to generate SO₂

The correct answer is option 2. Burning of Sulphur or roasting sulphide ores to generate SO₂.

The contact process is a widely used industrial method for the production of sulfuric acid (H2SO4), a key chemical in various industrial processes. Let's explore the detailed steps involved in the contact process:

1. Conversion of \(SO_2\) to \(SO_3\): Sulfur dioxide \((SO_2)\) is oxidized to sulfur trioxide \((SO_3)\) in the presence of a catalyst. The reaction typically takes place at high temperatures (around 450-500°C) and atmospheric pressure. The catalyst used is usually vanadium(V) oxide (V2O5) or platinum (Pt) supported on a porous material such as silica. The reaction is highly exothermic and reversible, and it is typically carried out in multiple stages to achieve higher conversion rates. The overall reaction can be represented as:

\(2\text{SO}_2 + \text{O}_2 \overset{catalyst}{\longrightarrow} 2\text{SO}_3 \)

2. Burning of Sulfur or Roasting Sulfide Ores to generate \(SO_2\): The contact process begins with the oxidation of sulfur or the burning of sulfur-containing ores (such as pyrite) to produce sulfur dioxide \((SO_2)\). Sulfur or sulfur-containing ores are combusted in the presence of oxygen to generate sulfur dioxide gas. The general equation for this reaction is:

\(\text{Sulfur (or sulfur-containing ores)} + \text{Oxygen} \rightarrow \text{Sulfur dioxide}\)

For example, the combustion of elemental sulfur can be represented as:

\(\text{S} + \text{O}_2 \rightarrow \text{SO}_2\)

Similarly, if sulfide ores are used, they are roasted (heated strongly in air) to convert the sulfide minerals to sulfur dioxide.

3. Absorption of \(SO_3\) in Sulfuric Acid:

The sulfur trioxide \((SO_3)\) produced in the previous step is then absorbed in concentrated sulfuric acid \((H_2SO_4)\) to form oleum \((H_2S_2O_7)\), also known as fuming sulfuric acid. The absorption of SO3 in sulfuric acid is an exothermic reaction and generates large amounts of heat. The resulting oleum is then diluted with water to form concentrated sulfuric acid of the desired strength. The overall reaction for the absorption of SO3 in sulfuric acid can be represented as:

\(\text{SO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{H}_2\text{S}_2\text{O}_7\)

4. Purifying \(SO_3\):

The oleum produced in the previous step is diluted with water to produce sulfuric acid of the desired concentration. The dilution process is carefully controlled to prevent excessive heat generation and splattering of acid. The resulting sulfuric acid can be further purified if necessary through processes such as distillation or treatment with additional water.

Overall, the contact process allows for the efficient production of sulfuric acid from sulfur or sulfur-containing ores through a series of well-controlled chemical reactions and process steps.