Question

Coal tar is obtained as a by-product during:
A) Destructive distillation of wood
B) Destructive distillation of coal
C) Destructive distillation of bones
D) Steam distillation of light oil

Answer 1

Hint: Many chemical processes yield a variety of compounds which found many uses in the industry. These compounds are called by-products because the process is carried out not to yield this particular product but as a common process.

Complete step by step answer:
We know the application of distillation is to separate the components of a mixture who show difference in their boiling points. It is an efficient separation technique.
Destructive distillation is a different type of distillation. It involves the heating of the unprocessed material to a high temperature. There will be limited or no supply of air. Sometimes, several catalysts are also used to accelerate the rate of the process.
During the heating of the compound at very high temperatures, the material decomposes to its constituent compounds and then they are recovered, mainly the volatile products, by condensation or by other methods. Therefore, the overall process in this is same as that of distillation but the differences are in the methods used. The limited or no supply of air is the main characteristic of destructive distillation.
The decomposed materials or constituent compounds are broken down by heat into solids, liquids or gases based on the nature and state of the compounds. Destructive distillation of coal is a best example for this. The products of this process include coke, coal gas, gas carbon, coal tar, ammonia liquor and coal oil.

So, the correct answer is Option B .

Additional Information:
The process of destructive distillation cracks or breaks up large molecules. It is a type of pyrolysis. It is done at very high temperatures like \[{\text{45}}{{\text{0}}^{\text{0}}}{\text{C - 50}}{{\text{0}}^{\text{0}}}{\text{C}}\]. The efficiency of the process depends mainly on the temperature used for the process.

Note: Destructive distillation is a widely used chemical process for the separation of various industrially important materials from several solid mixtures. Compounds like wood, coal etc. can undergo this process to yield many by-products.