In the purification of bauxite ore, a preliminary step in the production of aluminum, \(\left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}(\mathrm{aq})\) can be converted to \(\mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s})\) by passing \(\mathrm{CO}_{2}(\mathrm{g})\) through the solution. Write an equation for the reaction that occurs. Could HCl(aq) be used instead of \(\mathrm{CO}_{2}(\mathrm{g}) ?\) Explain.

Convert \(\left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}(\mathrm{aq})\) into \(\mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s})\) using \(\mathrm{CO}_{2}(\mathrm{g})\). The balanced chemical equation for this is: \[ \mathrm{CO}_{2}(\mathrm{g}) + \left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}(\mathrm{aq}) \rightarrow \mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s}) + \mathrm{H}_{2}\mathrm{O}(\mathrm{l}) + \mathrm{CO}_{3}^{2-} (\mathrm{aq})\] The reaction implies that the \(\mathrm{CO}_{2}(\mathrm{g})\) provides \(\mathrm{H}^{+}\) ions which combines with the OH groups of \(\left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}(\mathrm{aq})\) to form \(\mathrm{H}_{2}\mathrm{O}(\mathrm{l})\) and \(\mathrm{CO}_{3}^{2-} (\mathrm{aq})\), leaving behind \(\mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s}).\)

\(\mathrm{HCl}(\mathrm{aq})\) could be used as a substitute for \(\mathrm{CO}_{2}(\mathrm{g})\) as it would also provide H^+ ions to combine with the OH groups of \(\left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}(\mathrm{aq})\) to form \(\mathrm{H}_{2}\mathrm{O}(\mathrm{l})\), leaving behind \(\mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s})\) and \(\mathrm{Cl}^{-} (\mathrm{aq})\) . It should however be noted that this might change the pH and other properties of the resulting solution, and may also affect the overall process of bauxite purification, depending on the specific industrial process used.