Question

Ionization energy of $Al =5137\, kJ\, mol ^{-1}(\Delta H)$ hydration of $Al ^{3+}=-4665\, kJ\, mol ^{-1}.(\Delta H)_{\text {hydration }}$ for $Cl ^{-}=-381\, kJ$ $mol ^{-1} .$ Which of the following statement is correct

• A. $AlCl _{3}$ would remain covalent in aqueous solution
• B. Only at infinite dilution $AlCl _{3}$ undergoes ionization
• C. In aqueous solution $AlCl _{3}$ becomes ionic
• D. None of these

Answer 1

Answer: (C)

If $AlCl _{3}$ is present in ionic state in aqueous solution, therefore it has $Al ^{3+}$ and $3 Cl ^{-}$ ions

Standard heat of hydration of $Al ^{3+}$ and $3 Cl ^{-}$ ions $=-4665+3$ $\times(-381)\, kJ \,mol ^{-1}$

$=-5808 \,kJ \,/ mol$

Required energy of ionization of $Al =5137\, kJ \,mol ^{-1}$

$\therefore $ Hydration energy overcomes ionization energy

$\therefore AlCl _{3}$ would be ionic in aqueous solution