3.
\(2Al_2O_3\underrightarrow{^{^{đpnc,criolit}}}4Al+3O_2\)
\(2Al+3H_2SO_4\rightarrow Al_2\left(SO_4\right)_3+3H_2\)
\(Al_2\left(SO_4\right)_3+3BaCl_2\rightarrow2AlCl_3+3BaSO_4\)
\(AlCl_3+3NaOH\rightarrow Al\left(OH\right)_3+3NaCl\)
\(2Al\left(OH\right)_3\underrightarrow{^{^{t^0}}}Al_2O_3+3H_2O\)