\(\left\{ \begin{array}{l} N{a_2}O + {H_2}O \to 2NaOH\\ a\begin{array}{*{20}{c}} {}&{} \end{array}\begin{array}{*{20}{c}} {}&{} \end{array}\begin{array}{*{20}{c}} {\begin{array}{*{20}{c}} {}&{} \end{array}}&{} \end{array}2a\\ A{l_2}{O_3} + 2NaOH \to NaAl{O_2} + 2{H_2}O\\ a \to \begin{array}{*{20}{c}} {}&{} \end{array}2a \end{array} \right.\)

\(\\ Cu+2Fe^{3+}\rightarrow Cu^{2+}+2Fe^{2+}\\ \frac{a}{2} \ \ \leftarrow a\)

dư: \(\frac{a}{2}\)

\(BaCl_2+CuSO_4\rightarrow BaSO_4 \downarrow\)

\(\\Ba\rightarrow Ba(OH)_2 \\ a \hspace{40pt}a\)

\(\\ NaHCO_3+Ba(OH)_2\rightarrow BaCO_3 \downarrow + H_2O+NaOH \\ a \hspace{80pt}a\)