In the following sets of reactants which two sets best exhibit the amphoteric character of \(\mathrm{Al_2O_3\cdot xH_2O}\) ?
Set I: \(\mathrm{Al_2O_3\cdot xH_2O_{(s)}+OH^-_{(aq)}}\)
Set II: \(\mathrm{Al_2O_3\cdot xH_2O_{(s)}+H_2O_{(l)}}\)
Set III: \(\mathrm{Al_2O_3\cdot xH_2O_{(s)}+H^+_{(aq)}}\)
Set IV: \(\mathrm{Al_2O_3\cdot xH_2O_{(s)}+NH_{3(aq)}}\)
Set I: \(\mathrm{Al_2O_3\cdot xH_2O_{(s)}+OH^-_{(aq)}}\)
Set II: \(\mathrm{Al_2O_3\cdot xH_2O_{(s)}+H_2O_{(l)}}\)
Set III: \(\mathrm{Al_2O_3\cdot xH_2O_{(s)}+H^+_{(aq)}}\)
Set IV: \(\mathrm{Al_2O_3\cdot xH_2O_{(s)}+NH_{3(aq)}}\)
Show Hint
- 2 and 4
- 1 and 2
- 1 and 3
- 3 and 4
The Correct Option is C
Solution and Explanation
Set I: with \(\mathrm{OH^-}\), hydrated alumina dissolves as aluminate, \(\mathrm{Al_2O_3\cdot xH_2O+2OH^-\rightarrow2[Al(OH)_4]^-}\) (acts as an acid).
Set III: with \(\mathrm{H^+}\), it dissolves to give \(\mathrm{Al^{3+}}\) (\(\mathrm{[Al(H_2O)_6]^{3+}}\)), acting as a base.
Water (set II) and aqueous ammonia (set IV, a weak base) do not dissolve alumina.
So sets 1 and 3 show amphoterism.
Answer: (3) 1 and 3
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