Chemistry Class 12 NCERT Solutions: Chapter 7 The p Block Elements Part 8

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Q: 19. How is estimated quantitatively?


Quantitatively, ozone can be estimated with the help of potassium iodide. When ozone is made to react with potassium iodide solution buffered with a borate buffer , iodine is liberated. This liberated iodine can be titrated against a standard solution of sodium thiosulphate using starch as an indicator. The reactions involved in the process are given below.

Q: 20. What happens when sulphur dioxide is passed through an aqueous solution of salt?


acts as a reducing agent when passed through an aqueous solution containing salt. It reduces to i.e., ferric ions to ferrous ions.

Q: 21. Comment on the nature of two bonds formed in molecule. Are the two bonds in this molecule equal?


The electronic configuration of S is .

During the formation of , one electron from 3p orbital goes to the orbital and S undergoes hybridization. Two of these orbitals form sigma bonds with two oxygen atoms and the third contains a lone pair. P-orbital and d-orbital contain an unpaired electron each. One of these electrons forms pπ: pπ bond with one oxygen atom and the other forms bond with the other molecule. This is the reason has a bent structure. Also, it is a resonance hybrid of structures I and II.

Q 21 bond angel of sulphur dioxide.

Q 21 Bond Angel of Sulphur Dioxide.

Q 21 bond angel of sulphur dioxide.

Both bonds are equal in length and have a multiple bond character.

Q: 22. How is the presence of detected?


is a colourless and pungent smelling gas.

It can be detected with the help of potassium permanganate solution. When is passed through an acidified potassium permanganate solution, it decolonizes the solution as it reduces

Q: 23. Mention three areas in which plays an important role.


Sulphuric acid is an important industrial chemical and is used for a lot of purposes. Some important uses of sulphuric acid are given below.

(i) It is used in fertilizer industry. It is used to make various fertilizers such as ammonium sulphate and calcium super phosphate

(ii) It is used in the manufacture of pigments, paints, and detergents.

(iii) It is used in the manufacture of storage batteries.

Q: 24. Write the conditions to maximize the yield of by Contact process.


Manufacture of sulphuric acid by Contact process involves three steps.

1. Burning of ores to form

2. Conversion of to by the reaction of the former with

3. Absorption of in to give oleum

The key step in this process is the second step. In this step, two moles of gaseous reactants combine to give one mole of gaseous product. Also, this reaction is exothermic. Thus, in accordance with Le Chatelier’s principle, to obtain the maximum amount of gas, temperature should be low and pressure should be high.

Q: 25. Why is for in water?


It can be noticed that

This is because a neutral has a much higher tendency to lose a proton than the negatively charged . Thus, the former is a much stronger acid than the latter.