Solution of Chapter 11. The p - Block Elements (Chemistry Part-II Book)

Discuss the pattern of variation in the oxidation states of

(i) B to Tl

(ii) C to Pb.

How can you explain higher stability of BCl₃ as compared to TlCl₃ ?

Why does boron triflouride behave as a Lewis acid?

Consider the compounds, BCl₃ and CCl₄. How will they behave with water? Justify.

Is boric acid a protic acid? Explain.

Explain what happens when boric acid is heated.

Describe the shapes of BF₃ and BH₄^–. Assign the hybridization of boron in these species.

Write reactions to justify amphoteric nature of aluminium.

What are electron deficient compounds? Are BCl₃ and SiCl₄ electron deficient species? Explain.

Write the resonance structures of CO₃^2- and HCO₃^-.

What is the state of hybridization of carbon in (a) CO₃^2– (b) diamond (c) graphite?

Explain the difference in properties of diamond and graphite on the basis of their structures.

Rationalise the given statements and give chemical reactions:

• Lead(II) chloride reacts with Cl₂ to give PbCl₄.

• Lead(IV) chloride is highly unstable towards heat.

• Lead is known not to form an iodide, PbI₄.

Suggest reasons why the B–F bond lengths in BF₃ (130 pm) and BG₄^– (143 pm) differ.

If B–Cl bond has a dipole moment, explain why BCl₃ molecule has zero dipole moment.

Aluminium trifluoride is insoluble in anhydrous HF but dissolves on addition of NaF. Aluminium trifluoride precipitates out of the resulting solution when gaseous BF₃ is bubbled through. Give reasons.

Suggest a reason as to why CO is poisonous.

How is excessive content of CO₂ responsible for global warming?

Explain structures of diborane and boric acid.

What happens when

(a) Borax is heated strongly,

(b) Boric acid is added to water,

(c) Aluminium is treated with dilute NaOH,

(d) BF₃ is reacted with ammonia?

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) CO is heated with ZnO;

(d) Hydrated alumina is treated with aqueous NaOH solution.

Give reasons:

Conc. HNO₃ can be transported in aluminium container.

Give reasons:

A mixture of dilute NaOH and aluminium pieces is used to open drain.

Give reasons:

Graphite is used as lubricant.

Give reasons:

Diamond is used as an abrasive.

Give reasons:

Aluminium alloys are used to make aircraft body.

Give reasons:

Aluminium utensils should not be kept in water overnight.

Give reasons:

Aluminium wire is used to make transmission cables.

Explain why is there a phenomenal decrease in ionization enthalpy from carbon to silicon?

How would you explain the lower atomic radius of Ga as compared to Al?

What are allotropes? Sketch the structure of two allotropes of carbon namely diamond and graphite. What is the impact of structure on physical properties of two allotropes?

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

CO, B₂O₃, SiO₂, CO₂, Al₂O₃, PbO₂, Tl₂O₃

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

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

When metal X is treated with sodium hydroxide, a white precipitate (A) is obtained, which is soluble in excess of NaOH to give soluble complex (B). Compound (A) is soluble in dilute HCl 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.

What do you understand by (a) inert pair effect (b) allotropy and (c) catenation?

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. H₂SO₄ 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 X, Y and Z.

Write balanced equations for:

(i) BF₃ + LiH →

(ii) B₂H₆ + H₂O →

(iii) NaH + B₂H₆→

(iv)

(v) Al + NaOH →

(vi) B₂H₆ + NH₃→

Give one method for industrial preparation and one for laboratory preparation of CO and CO₂ each.

An aqueous solution of borax is

Boric acid is polymeric due to

The type of hybridisation of boron in diborane is

Thermodynamically the most stable form of carbon is

Elements of group 14

If the starting material for the manufacture of silicones is RSiCl₃, write the structure of the product formed.