Question

Write the balanced chemical equations when acidified \[\ce{K2Cr2O7}\] reacts with \[\ce{H2S}\].

Answer 1

When \[\ce{H2S}\] gas is passed through acidified \[\ce{K2Cr2O7}\] 

\[\ce{K2Cr2O7 + 4H2SO4 + 3H2S -> K2SO4  + Cr2(SO4)3 + 7H2O + 3S}\], the orange colour changes to green, indicating reduction of \[\ce{K2Cr2O7}\] to chromic sulphate and oxidation of \[\ce{S^{2-}}\] to sulphur.

\[\ce{K2Cr2O7 + 3H2S + 4H2SO4 -> K2SO4 + Cr2(SO4)3 + 7H2O + 3S↓}\]