EXERCISES
11.1 Discuss the pattern of variation in the oxidation states of
11.1 Discuss the pattern of variation in the oxidation states of
(i) B to Tl and (ii) C to Pb.
11.2 How can you explain higher stability of BCl3 as compared to
TlCl3 ?
11.3 Why does boron triflouride behave as a Lewis acid ?
11.4 Consider the compounds, BCl3 and CCl4. How will they behave
with
water ? Justify.
11.5 Is boric acid a protic acid ? Explain.
11.6 Explain what happens when boric acid is heated .
11.7 Describe the shapes of BF3 and BH4
–. Assign the hybridisation of boron in
these species.
11.8 Write reactions to justify amphoteric nature of aluminium.
11.9 What are electron deficient compounds ? Are BCl3 and SiCl4 electron
deficient species ? Explain.
11.10 Write the resonance structures of CO3
2–and HCO3
– .
11.11 What is the state of hybridisation of carbon in (a) CO3
2– (b) diamond
(c) graphite?
11.12 Explain the difference in properties of diamond and
graphite on the basis
of their structures.
11.13 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.
11.14 Suggest reasons why the B–F bond lengths in BF3 (130 pm)
and BF4
–
(143 pm) differ.
11.15 If B–Cl bond has a dipole moment, explain why BCl3 molecule
has zero
dipole moment.
11.16 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.
11.17 Suggest a reason as to why CO is poisonous.
11.18 How is excessive content of CO2 responsible for global
warming ?
11.19 Explain structures of diborane and boric acid.
11.20 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 ?
11.21 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) CO is heated with ZnO;
(d) Hydrated alumina is treated with aqueous NaOH solution.
11.22 Give reasons :
(i) Conc. HNO3 can be transported in aluminium container.
(ii) A mixture of dilute NaOH and aluminium pieces is used to
open
drain.
(iii) Graphite is used as lubricant.
(iv) Diamond is used as an abrasive.
(v) Aluminium alloys are used to make aircraft body.
(vi) Aluminium utensils should not be kept in water overnight.
(vii) Aluminium wire is used to make transmission cables.
11.23 Explain why is there a phenomenal decrease in ionization
enthalpy from
carbon to silicon ?
11.24 How would you explain the lower atomic radius of Ga as
compared to Al ?
11.25 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?
11.26 (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.
11.27 In some of the reactions thallium resembles aluminium,
whereas in others
it resembles with group I metals. Support this statement by
giving some
evidences.
11.28 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.
11.29 What do you understand by (a) inert pair effect (b)
allotropy and
(c) catenation?
11.30 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. 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.
11.31 Write balanced equations for:
(i) BF3 + LiH →
(ii) B2H6 + H2O →
(iii) NaH + B2H6 →
(iv) H3BO3 ⎯→Ä
(v) Al + NaOH →
(vi) B2H6 + NH3 →
11.32. Give one method for industrial preparation and one for
laboratory
preparation of CO and CO2 each.
11.33 An aqueous solution of borax is
(a) neutral (b) amphoteric
(c) basic (d) acidic
11.34 Boric acid is polymeric due to
(a) its acidic nature (b) the presence of hydrogen bonds
(c) its monobasic nature (d) its geometry
11.35 The type of hybridisation of boron in diborane is
(a) sp (b) sp2 (c) sp3 (d) dsp2
11.36 Thermodynamically the most stable form of carbon is
(a) diamond (b) graphite
(c) fullerenes (d) coal
11.37 Elements of group 14
(a) exhibit oxidation state of +4 only
(b) exhibit oxidation state of +2 and +4
(c) form M2– and M4+ ion
(d) form M2+ and M4+ ions
11.38 If the starting material for the manufacture of silicones
is RSiCl3, write the
structure
of the product formed.