a) $$2Mg + O_2 \rightarrow 2MgO$$
$$MgO + 2HCl \rightarrow MgCl_2 + H_2O$$
$$MgCl_2 + 2NaOH \rightarrow Mg(OH)_2\downarrow + 2NaCl$$
б) $$CuO + H_2SO_4 \rightarrow CuSO_4 + H_2O$$
$$CuSO_4 + 2NaOH \rightarrow Cu(OH)_2\downarrow + Na_2SO_4$$
$$Cu(OH)_2 \xrightarrow{t^o} CuO + H_2O$$
в) $$AlCl_3 + 3NaOH \rightarrow Al(OH)_3\downarrow + 3NaCl$$
$$2Al(OH)_3 \xrightarrow{t^o} Al_2O_3 + 3H_2O$$
$$Al_2O_3 + 6HCl \rightarrow 2AlCl_3 + 3H_2O$$
г) $$Na_2O + H_2O \rightarrow 2NaOH$$
$$2NaOH + H_2SO_4 \rightarrow Na_2SO_4 + 2H_2O$$
$$Na_2SO_4 + Ba(NO_3)_2 \rightarrow 2NaNO_3 + BaSO_4\downarrow$$