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Chapter 11 The p Block Elements Solutions

Question - 11 : -

What is the state of hybridisation of carbon in
(a) CO32- (b) diamond (c) graphite?

Answer - 11 : -

(a) CO32- (sp2) (b) Diamond (sp3) (c) Graphite (sp2)

Question - 12 : - Explain the difference in properties of diamond andgraphite on the basis of their structures.

Answer - 12 : -

  1. Sincediamond exists as a three dimensional network solid, it is the hardestsubstance known with high density and high melting point.
  2. Whereas in graphite, any two successive layers are held together by weak forcesof attraction. This makes graphite soft.
  3. Ingraphite, carbon atom is sp2 hybridized whereas in diamond,carbon atom is sp3 hybridized.
  4. Unlikediamond, graphite is good conductor of heat and electricity.

Question - 13 : -

  1. Rationalise the given statements and give chemicalreactions:
  2. Lead (II) chloride reacts with Cl2  togive PbCl4 .
  3. Lead (IV) chloride is highly unstable towards heat.
  4. Lead is known not to form an iodide Pbl4.

Answer - 13 : -

·        PbCl2  + Cl2 ———>PbCl4.
This is because Pb can show +2 oxidation state more easily than +4 due to inertpair effect.
heat

·        PbCl4 ———> PbCl2 +Cl2
Because Pb2+ is more stable than Pb4+ due to inert pair effect.

·        Pbl4 does not existbecause I- ion being a powerful reducing agent reduces Pb4+ ionto Pb2+ ion in solution.

·        Pb4+ + 2I– ——->Pb2+ + l2
Pb(IV)                      Pb(II)

Question - 14 : - Suggest reason why the B-F bond lengths in BF3 (130pm) and BF– (143 pm) differ.

Answer - 14 : -

In BF3 ‘B’ is sp2 hybridisedand in BF4– ‘B’ is sp3 hybridised.Thus, the difference in bond length is due to the state of hybridisation.

Question - 15 : - If B-Cl bond has a dipole moment, explain why BCl3 moleculehas zero dipole moment.

Answer - 15 : -

B-Cl bond has dipole moment becauseof polarity. In BCl3 since the molecule is symmetrical(planar). Thus the polarities cancel out.

Question - 16 : - Aluminiumtrifluoride 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 reason.

Answer - 16 : -

Since,anhydrous HF is covalent compound and weak acid due to high bond dissociationenergy. AlF3 doesnot dissolve in HF.
Whereas NaF is ionic compound.
3NaF + AlF3 ———>Na3[AlF6]
Na3[AlF6] + 3BF3(g) ——-> AlF3 + 3Na+ [BF]–

Question - 17 : - Suggesta reason as to why CO is poisonous.

Answer - 17 : -

COreacts with haemoglobin to form carboxyhaemoglobin which can destroy the oxygencarrying capacity of haemoglobin and the man dies of suffocation.

Question - 18 : - Howis excessive content of C02 responsiblefor global warming?

Answer - 18 : -

Excessof C02 absorbsheat radiated by the earth. Some of it is dissipated into the atmosphere whilethe remaining part is radiated back to the earth. As a result, temperature ofthe earth increases. This is the cause of global warming.

Question - 19 : - Explainstructures of diborane and boric acid.

Answer - 19 : - Boric acid contains planar BO33- ionswhich are linked together through hydrogen bonding shown in the fig.

Question - 20 : - Whathappens when
(a)Borax is heated strongly
(b)Boric acid is added to water
(c)Aluminium is treated with dilute NaOH
(d)BF3 is reactedwith ammonia?

Answer - 20 : -

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