Question

Coal tar is the main source of (a) aromatic compounds (b) alicyclic compounds (c) aliphatic compounds (d) nitro compounds.

Short answer

Coal tar is the main source of (a) aromatic compounds.

Step-by-step solution

Understand Coal Tar Composition

Coal tar is a byproduct of the process of coal gasification and carbonization, which is the process of heating coal in the absence of air. This process produces many different types of compounds including various hydrocarbons.

Identify the Types of Compounds

The different types of hydrocarbons can be categorized into three main groups: aromatic, alicyclic, and aliphatic. Aromatic hydrocarbons contain benzenoid structures, alicyclic compounds are typically non-aromatic with ring structures, and aliphatic compounds are straight or branched chain hydrocarbons.

Determine the Main Source

Coal tar is known to be rich in aromatic hydrocarbons, which include substances like benzene, naphthalene, anthracene, and phenols. These compounds are characterized by their stability and ring structures, which are common in the composition of coal tar.

Key concepts

Aromatic Compounds

Coal tar is a rich and complex mixture of organic compounds, with a significant portion being aromatic hydrocarbons. These molecules are characterized by their unique ring-shaped structure, known as a benzene ring, which is a hexagonal arrangement of six carbon atoms with alternating double bonds. Aromatic compounds have distinctive properties, such as high stability and the ability to undergo substitution reactions, where atoms or groups of atoms are replaced without disrupting the benzene ring.

Common examples found in coal tar include benzene, toluene, xylene, naphthalene, and anthracene. Naphthalene, for instance, is well-known for its use in mothballs, and benzene is a starting material for the synthesis of various plastics, resins, synthetic fibers, and rubbers.

These aromatic compounds have extensive uses in chemical industries, including the production of dyes, drugs, explosives, and as solvents for numerous chemical processes. Understanding their chemistry is crucial for applications ranging from manufacturing to environmental science.

Hydrocarbons

Hydrocarbons are organic compounds consisting exclusively of hydrogen and carbon atoms. They can be found in fossil fuels like coal, natural gas, and crude oil, and coal tar is no exception. Within the broad family of hydrocarbons, they can be further divided into three main categories: aromatic, alicyclic, and aliphatic.

Aromatic Hydrocarbons

As mentioned earlier, these contain one or more benzene rings and are known for their stability and fragrance.

Alicyclic Hydrocarbons

These are formed in ring structures but do not have the same stability as aromatic rings due to the lack of conjugated double bonds.

Aliphatic Hydrocarbons

These are characterized by straight or branched chains and are subdivided into alkanes, alkenes, and alkynes, based on the types of bonds they contain.

Coal tar predominantly contains aromatic hydrocarbons with complex structures, which stand apart from alicyclic and aliphatic compounds due to their electronic configurations that contribute to their unique chemical reactions and uses.

Coal Gasification

Coal gasification is a process that converts coal into carbon monoxide, hydrogen, and carbon dioxide. This is achieved by reacting the coal at high temperatures with a controlled amount of oxygen, steam, or a combination of these. It's different from burning, as gasification takes place in a low-oxygen environment, leading to the production of syngas or synthetic gas rather than combustion.

During the gasification of coal, a variety of valuable byproducts are produced, including coal tar. Coal tar itself undergoes further processing to extract the multitude of compounds it contains, such as the aforementioned aromatic hydrocarbons. The syngas produced during gasification is also a valuable resource and can be used to generate electricity, as a chemical feedstock, or as a fuel for heating.

The chemistry involved in coal gasification is complex and requires careful control to optimize the production of desirable byproducts while minimizing environmental impact. It plays a crucial role in the chemical industry and provides a way to utilize coal reserves in an efficient and potentially less polluting manner compared to conventional coal burning.