Chemistry Class 11 NCERT Solutions: Chapter 11 the p Block Elements Part 5

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Q: 20. What happens when

(A) Borax is heated strongly

(B) Boric acid is added to water

(C) Aluminium is treated with dilute

(D) is reacted with ammonia?


(A) When heated, borax undergoes various transitions. It first lises water moecules and swells. Then, it turns into a transparent liquid, solidifying to form a glass – like material called borax bead.

(B) When boric acid is added to water, it accepts electrons from ion.

(C) Al reacts with dilute to form sodium tetrahydroxoaluminate(III). Hydrogen gas is liberated in the process.

(D) (a Lewis acid) reacts with (a Lewis base) to form an adduct. This results in a complete octet around B in .

Q: 21. Explain the following reactions

(A) Silicon is heated with methyl chloride at high temperature in the presence of copper;

(B) Silicon dioxide is treated with hydrogen fluoride;

(C) is heated with ;

(D) Hydrated alumina is treated with aqueous solution.


(A) When silicon reactes with methyl chloride in the presence of copper (catalyst) and at a temperature of about 537 K, a class organosilicon polymers called methyl- substituted chlorosilanes ) are formed

(B) When silicon dioxide is heated with hydrogen fluoride , it forms silicon tetrafluoride . Usually, the bond is a strong bond and it resists any attack by halogens and most acids, even at a high temperature. However, it is attacked by HF.

The formed in this reaction can further react with HF to form hydrofluorosilicic acid

(C) When reacts with , it reduces to . acts as a reducing agent.

(D) When hydrated alumina is added to sodium hydroxide, the former dissolves in the latter because of the formation of sodium meta-aluminate.