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प्रश्न
Aluminium trifluoride is insoluble in anhydrous HF but dissolves on the addition of NaF. Aluminium trifluoride precipitates out of the resulting solution when gaseous BF3 is bubbled through. Give reasons.
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उत्तर
Hydrogen fluoride (HF) is a covalent compound and has a very strong intermolecular hydrogen-bonding. Thus, it does not provide ions and aluminium fluoride (AlF) does not dissolve in it. Sodium fluoride (NaF) is an ionic compound and when it is added to the mixture, AlF dissolves. This is because of the availability of free F–. The reaction involved in the process is:
\[\ce{AlF_3 + 3NaF -> \underset{Sodium hexafluoroaluminate (III)}{Na3[AlF6]}}\]
When boron trifluoride (BF3) is added to the solution, aluminium fluoride precipitates out of the solution. This happens because the tendency of boron to form complexes is much more than that of aluminium. Therefore, when BF3 is added to the solution, B replaces Al from the complexes according to the following reaction:
\[\ce{Na3[AlF6] + 3BF3 -> 3Na[BF4] + AIF3}\]
संबंधित प्रश्न
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(i) The two birdged hydrogen atoms and the two boron atoms lie in one plane;
(ii) Out of six B – H bonds two bonds can be described in terms of 3 centre 2-electron bonds.
(iii) Out of six B – H bonds four B – H bonds can be described in terms of 3 centre 2 electron bonds;
(iv) The four-terminal B – H bonds are two centre-two electron regular bonds.
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BCl3
When BCl3 is treated with water, it hydrolyses and forms [B[OH]4]– only whereas AlCl3 in acidified aqueous solution forms [Al(H2O)6]3+ ion. Explain what is the hybridisation of boron and aluminium in these species?
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PbX2 is more stable than PbX4.
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Pb4+ acts as an oxidising agent but Sn2+ acts as a reducing agent.
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\[\ce{X ->[Δ][370 K] HBO2 ->[Δ][> 370 K] Z}\]
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Describe the general trends in the following properties of the elements in Groups 13 and 14.
Metallic character
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Nature of halides
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Though fluorine is more electronegative than chlorine yet BF3 is a weaker Lewis acid than BCl3
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TlCl3, TlCl
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InCl3, InCl
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