Question

Aluminum chloride exists as dimer$\text{A}{{\text{l}} _ {2}} \text{C}{{\text{l}} _ {6}}$in the solid state as well as in solution. anhydrous aluminum chloride is hydrolyzed partly with the moisture in the atmosphere to give HCl gas. This HCl combined with the moisture in the air appears white in color of non-polar solvents such as benzene. When dissolved in water, it gives:
(a) ${{\text {} \! \! [\! \! \text {Al (OH} {{\text {)}} _ {6}} \text {} \! \!] \! \! \text {}} ^ {3-}} \text{+3HCl}$
(b) ${{\text {} \! \! [\! \! \text {Al (} {{\text{H}} _ {2}} \text{O} {{\text {)}} _ {6}} \text {} \! \!] \! \! \text {}} ^ {3+}} \text{+3HCl}$
(c) $\text{A}{{\text{l}} ^ {+3}} \text{+3C} {{\text{l}} ^ {-}}$
(d) $\text{A}{{\text{l}} _ {2}} {{\text{O}} _ {3}} \text{+6HCl}$

Answer 1

Hint: Aluminum chloride being unable to accommodate the large sized chlorine atoms around themselves so exists as dimer in solid state and in the solutions form and when it is dissolved in the water, it gets hydrolyzed to form ion which consist of the hydroxyl group i.e. -OH group.

Complete step by step solution:
Aluminum trichloride or the aluminum chloride is made up of the element’s aluminum and the chlorine and its chemical formula is $\text {Alca}{{\text{l}} _ {3}}$ and it is generally white in colour but it sometimes it appears yellow in color because of the impurity of Fe present in it.
Aluminum chloride is not present as such but it exists in the form of dimer having the chemical formula as $\text{A}{{\text{l}} _ {2}} \text{C}{{\text{l}} _ {6}}$. It is so because the size of both the aluminum and the chlorine atoms are very large and the aluminum atom cannot easily accommodate the four large sized chlorine atoms around themselves and hence, they exist in the form of dimer of aluminum chloride as $\text{A}{{\text{l}}_{2}}\text{C}{{\text{l}}_{6}} $both in the solid state as well as in the form of solutions too in the non-polar solvents such as benzene, ether etc.
The aluminum chloride is somewhat hydrolyzed to the HCl due to the moisture present in the air and when the aluminum chloride is dissolved in water, the following reaction occurs in the water:
$\text{A}{{\text{l}}_{2}}\text{C}{{\text{l}}_{6}}\text{+12}{{\text{H}}_{2}}\text{O}\to \text{2 }\!\![\!\!\text{ Al(OH}{{\text{)}}_{6}}{{\text{ }\!\!]\!\!\text{ }}^{3-}}\text{+12HCl}$
i.e. it gives ${{\text {} \! \! [\! \! \text {Al (OH} {{\text {)}} _ {6}} \text {} \! \!] \! \! \text {}} ^ {3-}} \text{+3HCl}$.

Hence, the option (a) is correct.

Note: Don’t write ${{\text{H}}_{2}}\text{O}$ in place of the -OH group in the brackets, otherwise the product formed would be wrong because the aluminum chloride dimer hydrolyses in water to give hydroxide ion i.e. ${{\text{ }\!\![\!\!\text{ Al(OH}{{\text{)}}_{6}}\text{ }\!\!]\!\!\text{ }}^{3-}}$and not ${{\text{ }\!\![\!\!\text{ Al(}{{\text{H}}_{2}}\text{O}{{\text{)}}_{6}}\text{ }\!\!]\!\!\text{ }}^{3+}}$ this.