Xác định số oxi hóa:

$\rm K\mathop{Mn}\limits^{+7}O_4+H_2\mathop{S}\limits^{-2}+H_2SO_4\dashrightarrow K_2SO_4+ \mathop{Mn}\limits^{+2}SO_4+\mathop{S}\limits^{0} +H_2O$

Quá trình trao đổi electron:

$\begin{array}{c|cc} \rm{\times \;5}&\rm{\mathop{S}\limits^{-2}\xrightarrow\ \mathop{S}\limits^{0}+2e}\\\rm {\times\;2}&\rm{\mathop{Mn}\limits^{+7}+5e\xrightarrow\ \mathop{Mn}\limits^{+2}}\\\end{array}$

Cân bằng:

$\rm 2KMnO_4+5H_2S+3H_2SO_4\to K_2SO_4+2MnSO_4+5S+8H_2O$