Chemistry Class 12 NCERT Solutions: Chapter 7 the P Block Elements Part 2 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Q: 7. Illustrate how copper metal can give different products on reaction with .

Ans:

Concentrated nitric acid is a strong oxidizing agent. It is used for oxidizing most metals. The products of oxidation depend on the concentration of the acid, temperature, and also on the material undergoing oxidation.

Q: 8. Give the resonating structures of .

Answer:

(1)

Q_8_1_The Resonating Structures of NO2 and N2 O5

(2)

Q_8_2_The Resonating Structures of NO2 and N2 O5

Q: 9. The HNH angle value is higher than , and angles. Why? [Hint: Can be explained on the basis of hybridisation in and only bonding between hydrogen and other elements of the group] .

Answer:

Hydride

The above trend in the bond angle can be explained on the basis of the electronegativity of the central atom. Since nitrogen is highly electronegative, there is high electron density around nitrogen. This causes greater repulsion between the electron pairs around nitrogen, resulting in maximum bond angle. We know that electronegativity decreases on moving down a group. Consequently, the repulsive interactions between the electron pairs decrease, thereby decreasing the bond angle.

Q: 10. Why does exist but does not ?

Answer:

(unlike ) lacks the d-orbital. This restricts nitrogen to expand its coordination number beyond four. Hence, does not exist.

Q: 11. Explain why is basic while is only feebly basic.

Answer:

is distinctly basic while is feebly basic.

Nitrogen has a small size due to which the lone pair of electrons is concentrated in a small region. This means that the charge density per unit volume is high. On moving down a group, the size of the central atom increases and the charge gets distributed over a large area decreasing the electron density. Hence, the electron donating capacity of group element hydrides decreases on moving down the group.

Q: 12. Nitrogen exists as diatomic molecule and phosphorus as . Why?

Answer:

Nitrogen owing to its small size has a tendency to form multiple bonds with itself. Nitrogen thus forms a very stable diatomic molecule, . On moving down a group, the tendency to form bonds decreases (because of the large size of heavier elements) . Therefore, phosphorus (like other heavier metals) exists in the state.

Q: 13. Write main differences between the properties of white phosphorus and red phosphorus.

Answer:

Difference between Wite and Red Phosphorus
White PhosphorusRed Phosphorus
It is a soft and waxy solid. It possesses a garlic smell.It is a hard and crystalline solid, without any smell.
It is poisonous.It is non-poisonous.
It is insoluble in water but soluble in carbon disulfide.It is insoluble in both water and carbon disulfide.
It undergoes spontaneous combustion in air.It is relatively less reactive.
In both solid and vapour states, it exists as a molecule.
Q_13_1_In Both Solid and Vapour States
It exists as a chain of tetrahedral units.
Q_13_Chain of Tetrahedral

Q: 14. Why does nitrogen show catenation properties less than phosphorus?

Answer:

Catenation is much more common in phosphorous compounds than in nitrogen compounds. This is because of the relative weakness of the single bond as compared to the single bond. Since nitrogen atom is smaller, there is greater repulsion of electron density of two nitrogen atoms, thereby weakening the single bond.

Q: 15. Give the disproportionation reaction of .

Answer:

On heating, orthophosphorus acid disproportionate to give orthophosphoric acid (H3PO4) and phosphine (PH3) . The oxidation states of P in various species involved in the reaction are mentioned below.

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