6 SnSO4 + 2 K2Cr2O7 + 14 H2SO4 → 3 Sn2(SO4)4 + 2 Cr2(SO4)3 + 2 K2SO4 + 14 H2O
This is an oxidation-reduction (redox) reaction:
6 SnII - 12 e- → 6 SnIV (oxidation)
4 CrVI + 12 e- → 4 CrIII (reduction)
SnSO4 is a reducing agent, K2Cr2O7 is an oxidizing agent.