Why benzene and other homologous compounds of benzene are called aromatic compounds?

  1. No.16. Why benzene and other homologous compounds of benzene are called aromatic compounds?

Answer. Those organic compounds which contain at least one benzene ring in their molecules are called aromatic compounds. They are called aromatic because of aroma. Aroma means smell.

  1. No.17. Which aromatic compound is used to keep insects away from clothes?

Answer. Naphthalene is an aromatic compound that is used to keep insects away from clothes. It decomposes at room temperature giving of very strong smell which keeps insects away from clothes.

ANSWER TO THE LONG QUESTIONS

  1. No 1. (a) How is coal formed? What are the different types of coal?

(b) Write down the composition and uses of different types of coal.

Answer.

(a)      Coal was formed by the decomposition of plants buried under the Earth’s crust millions of years ago. Conversion of wood into coal is called carbonization. It is a very slow bio-chemical process. It takes place in the absence of air under high pressure and high temperature over a long period of time (about 500 millions of years). Wood contains about 40% carbon, so depending upon the extent of carbonization process, four types of coal are found. These types differ with respect to carbon content, volatile matter and moisture. Peat, lignite, bituminous and anthracite are the types of coals.

coal_rank_blue

 

(b)      The composition and uses of coal are represented in table given below.

 

Type of Coal

 

Carbon contents

 

            Uses

 

Peat

 

60 %

 

It is inferior quality coal used in kiln.

 

Lignite

 

70 %

 

It is soft coal used in thermal power stations.

 

Bituminous

 

80 %

 

It is common variety of coal used as household coal.

 

Type of Coal

 

Carbon contents

 

          Uses

 

Anthracite

 

90%

 

It is superior quality hard coal that is used in industry.

 

  1. No 2. (a) What is destructive distillation of coal?

(b) Name the different types of products obtained by the destructive distillation of coal.

Answer.

(a);     Coal has become a major source of organic compounds. These compounds are obtained by destructive distillation. The strong heating of coal in the absence of air is called destructive distillation. Coal contains elements like carbon, hydrogen, oxygen, nitrogen, and sulphur. So destructive distillation of coal provides a large number of organic compounds along with a few inorganic compounds.

(b)     Different types of products of coal;

(i)       Coal Gas is mixture of hydrogen, methane and carbon monoxide. It produces heat when burnt in air. Therefore, it is mainly used as a fuel in industry,It is also used to provide an inert or reducing atmosphere in various metallurgical processes.

(ii)      Ammonical Liquor is a solution of ammonia gas in water. It is used to prepare nitrogenous fertilizers. For example, when it is treated with sulphuric acid, it produces ammonium sulphate, fertilizer.

(iii)     Coal-Tar is a thick black liquid. It is admixture of more than 200 different organic compounds, mostly aromatic. These compounds are separated by fractional distillation. Some of the important aromatic compounds are benzene, phenol, toluene, aniline, etc. These chemicals are used to synthesize drugs, dyes, explosives, paints, varnishes, plastics, synthetic fiber and pesticides. Besides these valuable chemicals, the black residue of the coal tar is called pitch. It is used for surfacing of roads and roofs.

(iv)      Coke is 98% carbon. It is left behind residue of coal. When coal is subjected to destructive distillation, it loses all its volatile components and leaves behind a solid residue called coke. It is mainly used as a reducing agent in the extraction of metals | especially iron. It is also used as fuel.

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