Explain why is there a phenomenal decrease in ionization enthalpy from carbon to silicon.
Because there is increase in atomic size on moving from carbon to silicon, the screening effect increases. Thus the force of attraction of nucleus for the valence electron decreases as compared to carbon. Thus the ionization enthapy decreases from carbon to silicon.
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 cone.H2SO4is added to a hot solution of X, white crystal of an acid Z separates out.
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.
Give reasons:
(a) Why do Boron halides form addition compound with NH3?
(b) The tendency for catenation decreases down the group in Group 14.
(c) PbO2 is a stronger oxidising agent than SnO2.
Give one method for industrial preparation and one for laboratory preparation of CO and C02 each.
The+1 oxidation state in group 13 and +2 oxidation state in group 14 becomes more and more stable with increasing atomic number. Explain.
Match the species given in Column I with the properties mentioned in Column II.
| Column I | Column II |
| (i) BF4– | (a) Oxidation state of central atom is +4 |
| (ii) A1C13 | (b) Strong oxidising agent |
| (iii) SnO | (c) Lewis acid |
| (iv) Pb02 | (d) Can be further oxidised |
| (e) Tetrahedral shape |
Give reasons:
(i) Cone. 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.
What is meant by catenation? Why does ‘C show the property of catenation to maximum extent?
Give the chemical reactions as an evidence for each of the following observations.
(i) Tin (II) is a reducing agent whereas lead (II) is not.
(ii) Gallium (I) undergoes disproportionation reaction.
The reason for small radius of Ga compared to Al is_________ .
(a) poor screening effect of d and f orbitals
(b) increase in nuclear charge
(c) presence of higher orbitals
(d) higher atomic number
Which of the following statements are correct?
(a) Fullerenes have dangling bonds.
(b) Fullerenes are cage-like molecules.
(c) Graphite is thermodynamically most stable allotrope of carbon.
(d) Graphite is slippery and hard and therefore used as a dry lubricant in
Explain the following:
In some of the reactions thallium resembles aluminium, whereas in others it resembles with group 1 metals. Support this statement by giving some evidences.
(a) Why do Boron halides form addition compound with NH3?
(b) Assign appropriate reason for each of the following observations:-
(i) Anhydrous AlCl3 is used as a catalyst in many organic reactions.
(ii) No form of elemental silicon is comparable to graphite.
Give the chemical reaction as an evidence for each of the following observations.
(i) Tin (II) is a reducing agent whereas lead (II) is not.
(ii) Gallium (I) undergoes disproportionation reaction.
Boric acid is an acid because its molecule
(a) contains replaceable H+ ion
(b) gives up a proton.
(c)accepts OH–from water releasing proton.
(d) combines with proton from water molecule.
In the structure of diborane
(a) all hydrogen atoms lie in one plane and boron atoms lie in a plane perpendicular to this plane.
(b) 2 boron atoms and 4 terminal hydrogen atoms lie in the same plane and 2 bridging hydrogen atoms lie in the perpendicular plane.
(c) 4 bridging hydrogen atoms and boron atoms lie in one plane and two terminal hydrogen atoms lie in a plane perpendicular to this plane.
(d) all the atoms are in the same plane.
Explain the following:
(i) C02 is a gas whereas Si02 is a solid.
(b) Silicon forms SiF62- ion whereas corresponding fluoro compound of carbon is not known.
Carbon and silicon both belong to the group 14, but in spite of the stoichiometric similarity, the dioxides (i.e., carbon dioxide and silicon dioxide) differ in their structures. Comment.
What are electron deficient compounds? Are BCl3 and SiCl4 electron deficient species? Explain.
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.
Ionisation enthalpy (∆ tH1 kJ mol-1) for the elements of Group 13 follows the order.
(a) B > A1 > Ga > In > T1
(b) B < A1 < Ga< In
(d) B > A1 < Ga > In < T1
Which of the following statements are correct? Answer on the basis of figure.
(a) The two bridged hydrogen atoms and the two boron atoms lie in one plane.
(b) Out of six B – H, bonds two bonds can be described in terms of 3 centre 2-electron bonds.
(c) Out of six B – H bonds four B – H bonds can be described in terms of 3 centre 2 electron bonds.
(d) The four terminal B – H bonds are two centre-two electron regular bonds.
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 reason.
Explain why is there a phenomenal decrease in ionization enthalpy from carbon to silicon.
Boric acid is polymeric due to
(a) its acidic nature (b) the presence of hydrogen bonds
(c) its monobasic nature (d) its geometry
Thermodynamically the most stable form of carbon is
(a)diamond (b) graphite (c) fullerenes (d) coal