Amphoteric substances are those that can react with both acids and bases. Aluminium reacts with HCl to liberate $\mathrm{H}_2$ gas as : $\mathrm{2Al}_{(s)} + \mathrm{6HCl}_{(aq)}$ → $\mathrm{2Al}^{3+}_{(aq)} + \mathrm{6Cl}^{-}_{(aq)} + \mathrm{3H}_{2(g)}$ Aluminium can react with aqueous alkali and liberate hydrogen gas. $\mathrm{2Al}_{(s)} + \mathrm{2NaOH}_{(aq)} + \mathrm{6H_2O}_{(l)}$ → $\underset{\text{Sodium tetrahydroxoaluminate (III)}}{\mathrm{2Na}^{+}[\mathrm{Al(OH)}_4]^{-}_{(aq)}} + \mathrm{3H}_2$ ↑