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

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Q: 9. What happens when is heated?

Answer:

All the bonds that are present in are not similar. It has three equatorial and two axial bonds. The equatorial bonds are stronger than the axial ones. Therefore, when is heated strongly, it decomposes to form .

Q: 10. Write a balanced equation for the hydrolytic reaction of in heavy water.

Answer:

Therefore, the reaction can be written as

Q: 11. What is the basicity of ?

Answer:

Since there are three groups present in , its basicity is three i.e., it is a tribasic acid.

Q: 12. What happens when is heated?

Answer:

, on heating, undergoes disproportionation reaction to form and . The oxidation numbers of in , , and are , and respectively. As the oxidation number of the same element is decreasing and increasing during a particular reaction, the reaction is a disproportionation reaction.

Q: 13. List the important sources of sulphur.

Answer:

Sulphur mainly exists in combined form in the earth’s crust primarily as sulphates and sulphides .

Q: 14. Write the order of thermal stability of the hydrides of Group elements.

Answer:

The thermal stability of hydrides decreases on moving down the group. This is due to a decrease in the bond dissociation enthalpy of hydrides on moving down the group.

Therefore,

Q 14 Thermal Stability Decreases

Q 14 Thermal Stability Decreases

Q 14 Thermal Stability Decreases

Q: 15. Why is a liquid and a gas?

Answer:

has oxygen as the central atom. Oxygen has smaller size and higher electronegativity as compared to sulphur. Therefore, there is extensive hydrogen bonding in , which is absent in . Molecules of are held together only by weak van der Waal’s forces of attraction.

Hence, exists as a liquid while as a solid.

Q: 16. Which of the following does not react with oxygen directly?

Zn, Ti, Pt, Fe

Answer:

Pt is a noble metal and does not react very easily. All other elements Zn, Ti, Fe are quite reactive. Hence, oxygen does not react with platinum (Pt) directly.

Q: 17. Complete the following reactions:

(i)

(ii)

Answer:

(i)

(ii)

Q: 18. Why does act as a powerful oxidising agent?

Answer:

Ozone is not a very stable compound under normal conditions and decomposes readily on heating to give a molecule of oxygen and nascent oxygen. Nascent oxygen, being a free radical, is very reactive.

Therefore, ozone acts as a powerful oxidising agent.