First slide

Atomic and physical properties

Question

The aqueous solution of AlCl₃ contains Al³⁺ ions because

Moderate

A

Its higher hydration energy compensates its high ionisation energy
B

Its higher ionisation energy compensates its higher hyhdration energy
C

Its hydration energy is same as its ionisation energy
D

Al is amphoteric metal

Solution

${AlCl}_{3} + 6 H_{2} O \to [Al {(H_{2} O)}_{6}] {Cl}_{3} \approx {[Al {(H_{2} O)}_{6}]}^{+ 3} + 3 {Cl}^{-}$
In $[Al {(H_{2} O)}_{6}] {Cl}_{3}$ the oxidation state of Al is +3 .
$Al\xrightarrow[{ + I{E_1}}]{{ - {e^ - }}}A{l^{ + 1}}\xrightarrow[{ + I{E_2}}]{{ - {e^ - }}}A{l^{ + 2}}\xrightarrow[{ + I{E_3}}]{{ - {e^ - }}}A{l^{ + 3}}\xrightarrow[{ - H.E}]{{n{H_2}O}}A{l^{ + 3}}$
Ionisation energy is absorbed energy for the removal of three electrons.
Where as hydration energy is released energy during hydration of one mole of Al⁺³ ions.
In the above reaction both the processess are involved but hydration energy is greater than that of ionisation energy.
Hence removal of three electrons easily takes place and gives Al⁺³ ion in solution.

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