Question

Discuss the methods for the preparation of sulphuric acid and give its properties.

Short answer

Sulphuric acid can be prepared in the lab by reacting sulphur trioxide with water, while commercially it is prepared by Contact process involving oxidation of sulphur dioxide to sulphur trioxide, and then absorption in sulphuric acid or water. It's a dense, colorless, oily liquid that is soluble in water, a strong acid, and a powerful dehydrating agent.

Step-by-step solution

Discussion on the preparation of sulphuric acid

Sulphuric acid, \(H_2SO_4\), can be prepared in the laboratory by the reaction of sulphur trioxide with water. However, commercially, it is prepared by the Contact process. This process involves the oxidation of sulphur dioxide to form sulphur trioxide, which is then absorbed in sulphuric acid or water to give more of the acid.

Description of Contact process

The Contact process involves three major steps. 1) Burning of Sulphur or Iron Pyrites in Air to get Sulphur Dioxide. 2) Conversion of Sulphur Dioxide into Sulphur Trioxide by Oxidation using Vanadium (V) Oxide as Catalyst. 3) Absorption of Sulphur Trioxide in sulphuric acid or water to get more of the acid.

Discussion on the properties of sulphuric acid

Sulphuric acid has several key properties. It is a dense, colorless, oily liquid that is soluble in water in all proportions and it releases considerable heat when diluted. It is a strong acid and exhibits typical acidic behavior. It is also a powerful dehydrating agent and will extract water from many materials, including carbohydrates and other organic matter.

Key concepts

Contact Process

The Contact process is the industrial method for the production of sulphuric acid, which is a vital substance in various manufacturing sectors. It is preferred for its efficiency and ability to produce acid of high purity. The process begins with the combustion of sulfur or iron pyrites (FeS2) to generate sulphur dioxide (SO2). The sulphur dioxide is then oxidized to sulphur trioxide (SO3) in the presence of a catalyst such as Vanadium (V) Oxide. This oxidation is critical, for the direct combination of sulphur dioxide with water is not practical due to the sulphur trioxide's heightened affinity for water. Finally, the sulphur trioxide is absorbed in water or sulphuric acid to yield more concentrated sulphuric acid.

Detailed attention to the catalyst's role, optimal temperature, and pressure is crucial for the success of this process. The temperature must be controlled to maximize yield and minimize side reactions, while pressure and the concentration of reactants are adjusted according to Le Chatelier's principle to favor the formation of sulphur trioxide.

Properties of Sulphuric Acid

Sulphuric acid exhibits a set of remarkable properties that makes it an essential chemical in many industries. It is a dense, colorless, and oily liquid, reflecting its high molecular weight. When dissolved in water, sulphuric acid is a very strong acid – it completely dissociates into hydrogen ions (H+) and sulphate ions (SO4 2-), which accounts for its significant acidity and its ability to conduct electricity.

Its reaction with water is highly exothermic, releasing significant heat. This aspect requires careful and gradual dilution of the acid into water to prevent splashing and boiling, which might lead to accidents. On a more practical front, the low volatility of sulphuric acid makes it convenient for industrial use, as it does not readily evaporate and can be stored and handled with relative ease.

Sulphur Trioxide Oxidation

Sulphur trioxide oxidation is a pivotal step in the Contact process, as it forms the heart of sulphuric acid manufacture. After the production of sulphur dioxide, it is oxidized to sulphur trioxide in a highly controlled environment. This reaction is facilitated by a vanadium (V) oxide catalyst. The equation for this reaction is: \[2 SO_2(g) + O_2(g) \rightarrow 2 SO_3(g)\].

The catalyst plays a crucial role by lowering the activation energy required for the reaction, allowing the reaction to proceed at a faster rate and at a more moderate temperature. Furthermore, maintaining specific temperatures and pressures is vital to ensure the optimal conversion of SO2 to SO3. Any deviation from the ideal conditions can lead to reduced efficiency and yield. In practice, converters with multiple catalyst beds are used to maximize the production of sulphur trioxide.

Dehydrating Agent

One of the standout chemical characteristics of sulphuric acid is its ability as a powerful dehydrating agent. This means it has a strong tendency to absorb water from substances, often leading to vigorous and sometimes violent reactions. This property is exhibited when sulphuric acid interacts with organic compounds such as carbohydrates; where dehydration can occur resulting in the charring of the substance as the acid strips away molecules of water (H2O).

The dehydration capability of sulphuric acid is used in many chemical synthesis and purification processes. It is important for students to understand that handling sulphuric acid requires extreme caution due to this property, as contact with skin can result in severe burns due to dehydration and subsequent tissue damage.