Lời giải:\(\begin{array}{l} {\rm{K}}\mathop {\rm{I}}\limits^{ - 1} {\rm{ + }}{{\rm{H}}_{\rm{2}}}\mathop {\rm{S}}\limits^{ + 6} {{\rm{O}}_{\rm{4}}}{\rm{\;}} \to {{\overset{\text{0}}{\mathop{\text{I}}}\,}_{\text{2}}}{\rm{\; + }}{{\rm{H}}_{\rm{2}}}\mathop {\rm{S}}\limits^{ - 2} {\rm{ + }}{{\rm{K}}_{\rm{2}}}\mathop {\rm{S}}\limits^{ + 6} {{\rm{O}}_{\rm{4}}}{\rm{\; + }}{{\rm{H}}_{\rm{2}}}{\rm{O}}\\ \left\{ \begin{array}{l} 4 \times \\ 1 \times \end{array} \right.\left| \begin{array}{l} 2\mathop {\rm{I}}\limits^{ - 1} \to {{\overset{\text{0}}{\mathop{\text{I}}}\,}_{\text{2}}} + 2\\ \mathop {\rm{S}}\limits^{ + 6} + 8e \to \mathop {\rm{S}}\limits^{ - 2} \end{array} \right.\\ {\rm{8K}}\mathop {\rm{I}}\limits^{ - 1} {\rm{ + 5}}{{\rm{H}}_{\rm{2}}}\mathop {\rm{S}}\limits^{ + 6} {{\rm{O}}_{\rm{4}}}{\rm{\;}} \to 4{{\overset{\text{0}}{\mathop{\text{I}}}\,}_{\text{2}}}{\rm{\; + }}{{\rm{H}}_{\rm{2}}}\mathop {\rm{S}}\limits^{ - 2} {\rm{ + 4}}{{\rm{K}}_{\rm{2}}}\mathop {\rm{S}}\limits^{ + 6} {{\rm{O}}_{\rm{4}}}{\rm{\; + 4}}{{\rm{H}}_{\rm{2}}}{\rm{O}} \end{array} \)
Vậy hệ số cân bằng của H2SO4 là 5.
