Chemistry Class 11 NCERT Solutions: Chapter 11 the p Block Elements Part 7

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Q: 26.

(A) Classify following oxides as neutral, acidic, basic, or amphoteric:

(B) Write suitable chemical equations to show their nature.

Answer:

(1)

(2)

Being acidic, it reacts with bases to form salts. It reacts with to form sodium metaborate.

(3)

Being acidic, it reacts with bases to form salts. It reacts with to form sodium silicate.

(4)

Being acidic, it reacts with bases to form salts. It reacts with to form sodium carbonate.

(5)

Amphoteric substances react with both acids and bases. reacts with both and .

(6)

Amphoteric substances react with both acids and bases. reacts with both and .

(7)

Being basic, it reacts with acids to form salts. It reacts with HCl to form thallium chloride.

Q: 27. In some of the reactions thallium resembles aluminium, whereas in others it resembles with group I metals. Support this statement by giving some evidences.

Answer

Thallium belongs to group 13 of the periodic table. The most common oxidation state for this group is +3. However, heavier members of this group also display the +1 oxidation state. This happens because of the inert pair effect. Aluminium displays the +3oxidation state and alkali metals display the +1 oxidation state. Thallium displays both the oxidation states. Therefore, it resembles both aluminium and alkali metals. Thallium, like aluminium, forms compounds such as and . It resembles alkali metals in compounds and .

Q: 28. When metal is treated with sodium hydroxide, a white precipitate (A) is obtained, which is soluble in excess of to give soluble complex (B). Compound (A) is soluble in dilute to form compound (C). The compound (A) when heated strongly gives (D), which is used to extract metal. Identify (X), (A), (B), (C) and (D). Write suitable equations to support their identities.

Answer:

The given metal X gives a white precipitate with sodium hydroxide and the precipitate dissolves in excess of sodium hydroxide. Hence, X must be aluminium. The white precipitate (compound A) obtained is aluminium hydroxide. The compound B formed when an excess of the base is added is sodium tetrahydroxoaluminate(III).

Now, when dilute hydrochloric acid is added to aluminium hydroxide, aluminium chloride (compound C) is obtained.

Also, when compound A is heated strongly, it gives compound D. This compound is used to extract metal X. Aluminium metal is extracted from alumina. Hence, compound D must be alumina.