JEE Main 2014 — Chemistry Inorganic Chemistry

2014mcqhard

In the following sets of reactants which two sets best exhibit the amphoteric character of Al $_{2}$ O $_{3}$ . xH $_{2}$ O ?

$\begin{matrix} \text{Set I} & {\text{Al}}_{2} {\text{O}}_{3} \cdot {\text{xH}}_{2} {\text{O}}_{( \text{s} )} + {\text{OH}}_{( \text{aq} )}^{-} \\ \text{Set II} & {\text{Al}}_{2} {\text{O}}_{3} \text{x} \cdot {\text{H}}_{2} {\text{O}}_{( \text{s} )} + {\text{H}}_{2} {\text{O}}_{( \text{l} )} \\ \text{Set III} & {\text{Al}}_{2} {\text{O}}_{3} \text{x} \cdot {\text{H}}_{2} {\text{O}}_{( \text{s} )} + {\text{H}}_{( \text{aq} )}^{+} \\ \text{Set IV} & {\text{Al}}_{2} {\text{O}}_{3} \cdot {\text{xH}}_{2} {\text{O}}_{( \text{s} )} + {\text{NH}}_{ 3 ( \text{aq} ) } \end{matrix}$

Official previous-year question

Held on 9 Apr 2014 · Verified 6 Jul 2026.

Options

A
2 and 4
B
1 and 2
C
1 and 3
D
3 and 4

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Solution

For a substance to be called amphoteric, it should be able to react as a base as well as an acid. Hence, when it is reacted with a base, it should act as an acid, and when it is reacted with an acid, it should behave as a base.

The reactions for amphoteric nature of Al $_{2}$ O $_{3}$ . x H $_{2}$ O(s) are

${\text{Al}}_{2} {\text{O}}_{3} . x {\text{H}}_{2} \text{O} ( \text{s} ) \overset{{\text{OH}}_{\text{aq}}^{-}}{\rightarrow } \text{Al} { ( \text{OH} ) }_{4}^{-} aq$

Aluminate anion

${\text{Al}}_{2} {\text{O}}_{3} . x {\text{H}}_{2} \text{O} ( \text{s} ) \overset{{\text{H}}_{\text{aq}}^{+}}{\rightarrow } { [ \text{Al} { ( {\text{H}}_{2} \text{O} ) }_{6} ] }_{\text{aq}}^{ 3 + }$ .

[Al(H $_{2}$ O) $_{6}$ ] $^{3+}$ is octahedral complex ion

[Al(OH) $_{4}$ ] $^{-1}$ tetrahedral at pH = 13

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Solution

The reactions for amphoteric nature of Al $_{2}$ O $_{3}$ . x H $_{2}$ O(s) are

${\text{Al}}_{2} {\text{O}}_{3} . x {\text{H}}_{2} \text{O} ( \text{s} ) \overset{{\text{OH}}_{\text{aq}}^{-}}{\rightarrow } \text{Al} { ( \text{OH} ) }_{4}^{-} aq$

Aluminate anion

[Al(H $_{2}$ O) $_{6}$ ] $^{3+}$ is octahedral complex ion

[Al(OH) $_{4}$ ] $^{-1}$ tetrahedral at pH = 13

JEE Main 2014 — Chemistry Inorganic Chemistry

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JEE Main 2014 — Chemistry Inorganic Chemistry

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