Chapter 3 chemistry XII

Question 3.1: What is the action of an aqueou solution of Borax on Litmus?
Answer: When borax undergoes hydrolysis it forms weak acid) boric acid) and strong base (sodium hydroxide). Due to strong base aqua solution of borax is alkaline and it turns red litmus paper to blue.

Question 3.2: Give equation to represent the following reactions.
Answer: (I) Borax is heated with Cobalt oxide

(II) Alumina is heated with sodium hydroxide solution

Question 3.3: Why is aluminium not found as a free state? explain the chemistry of borax bead test
Answer: Aluminium is the third most abundant element after oxygen and sulphur. Its amount in the earth crust is 8.3 %. It is very highly reactive element so it does not occur in free state. Generally, it is found as aluminium silicates mineral such as kaolin, mica, feldspar etc.

Question 3.4: How does orthoboric acid react with
(a) sodium hydroxide.
(b) ethyl alcohol

Question 3.5: how will you convert boric acid into borax and vice versa.
Answer:

Question 3.7: Why are liquid silicone are prefferd than ordinary organic lubricants.
Answer: Due to following reasons, we prefer silicone oil to the petroleum oil as a lubricant.

Silicone oil is thermally stable and its viscosity is less affected by temperature. In machine silicone oil does not become thin and flow out at high temperature.
In the same way, when temperature decreases from 100 to zero degree centigrade, viscosity of petrol increases about 100 times and that of silicones increases only four times.
Furthermore, at a high temperature around about 300 degree centigrade silicon remains free from acid formation and oxidation.

Question 3.8: Carbon dioxide is nonpolar in nature.
Answer: carbon dioxide is linear molecule there are two dipoles in CO2. These two dipoles are equal and opposite, so they cancel Each Other therefore net dipole moment of carbon dioxide is zero and it is non polar nature
Question 3.9: Carbon dioxide is acidic in nature.
Answer: Carbon dioxide reacts with water to give carbonic acid. Carbonic acid is a weak acid which turns blue Litmus to Red and CO2 is acidic in nature. Next

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