Question

Molten ${\mathrm{AlCl}}_3$is a poor conductor of electricity while hydrated ${\mathrm{AlCl}}_3$is a very good conductor. How do you account for this? Also, explain the nature of bonding in the product.

Answer 1

Covalent compound - Covalent compounds are formed by the sharing of electrons between atoms. Example: ${\mathrm{O}}_2,{\mathrm{N}}_2,{\mathrm{Cl}}_2$

${\mathrm{AlCl}}_3$is covalent because of its small size and high nuclear charge${\mathrm{Al}}^{+3}$. But when ${\mathrm{AlCl}}_3$is dissolved in water, ${\mathrm{Al}}^{+3}$ ions get surrounded by water molecules using coordinate covalent bonds in which a lot of energy is liberated.

${\mathrm{AlCl}}_3\left(\mathrm{s}\right)+6{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\left[\mathrm{Al}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{+3}\left(\mathrm{aq}\right)$

Thus, ${\mathrm{AlCl}}_3$ gets dissolved in an aqueous medium in which mobile hydrated aluminium and chloride ions are present, and hence, it conducts electricity due to the mobility of these ions. However, molten ${\mathrm{AlCl}}_3$exists as a molecule, and thus, is a bad conductor of electricity.