Chemistry Class 11 NCERT Solutions: Chapter 11 the p Block Elements Part 8

Q: 29. What do you understand by

(A) Inert pair effect

(B) Allotropy and

(C) Catenation

Answer:

(A) Inert pair effect

As one moves down the group, the tendency of S - block electrons to participate in chemical bonding decreases. This effect is known as inert pair effect. In case of group 13 elements, the electronic configuration is Equation and their group valency is +3. However, on moving down the group, the +1 oxidation state becomes more stable. This happens because of the poor shielding of the Equation electrons by the d and f electrons. As a result of the poor shielding, the Equation electrons are held tightly by the nucleus and so, they cannot participate in chemical bonding.

(B) Allotropy

Allotropy is the existence of an element in more than one form, having the same chemical properties but different physical properties. The various forms of an element are called allotropes. For example, carbon exists in three allotropic forms: diamond, graphite, and fullerenes.

(C) Catenation

The atoms of some elements (such as carbon) can link with one another through strong covalent bonds to form long chains or branches. This property is known as catenation. It is most common in carbon and quite significant in Si and S.

Q: 30. A certain salt X, gives the following results.

(i) Its aqueous solution is alkaline to litmus

(ii) It swells up to a glassy material Y on strong heating

(iii) When conc. Equation is added to a hot solution of X, white crystal of an acid Z separates out.

Write equations for all the above reactions and identify Equation and Equation .

Answer:

The given salt is alkaline to litmus. Therefore, X is a salt of a strong base and a weak acid. Also, when X is strongly heated, it swells to form substance Y. Therefore, X must be borax.

When borax is heated, it loses water and swells to form sodium metaborate. When heating is continued, it solidifies to form a glassy material Y. Hence, Y must be a mixture of sodium metaborate and boric anhydride.

Equation

Equation

When concentrated acid is added to borax, white crystals of orthoboric acid Equation are formed.

Equation

Q: 31. Write balanced equations for:

(i) Equation

(ii) Equation

(iii) Equation

(iv) Equation

(v) Equation

(vi) Equation

Answer:

(i) Equation

(ii) Equation

(iii) Equation

(iv)

(v) Equation

(vi) Equation

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