1.

Give reasons for the following:(i) CCl4 is immiscible in water, whereas SiCl4 is easily hydrolysed.(ii) Carbon has a strong tendency for catenation compared to silicon.

Answer»

(i) CCl4 is a covalent compound while H2O is a polar compound. Therefore, it is insoluble in water. Alternatively, CCl4 is insoluble in water because carbon does not have orbitals to accommodate the electrons donated by oxygen atom of water molecules. As a result, there is no interaction between CCland water molecules and hence CCl4 is insoluble in water. On the other hand, SiCl4 has d-orbitals to accommodate the lone pair of electrons donated by oxygen atom of water molecules. As a result, there is a strong interaction between SiCl4 and water molecules. Consequently, SiClundergoes hydrolysis by water to form silicic acid.

(b)  The bond dissociation energy decreases rapidly as the atomic size increases. Since the atomic size of carbon is much smaller (77 pm) as compared to that of silicon (118 pm), therefore, carbon-carbon bond dissociation energy is much higher (348 kJ mol-1) than that of silicon-silicon bond (297 kJ mol-1). Hence, because C - C bonds are much stronger as compared to Si-Si bonds, carbon has a much higher tendency for catenation than silicon.



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