4 KCr2O7 + 28 H2SO4 + 14 SnCl2 → 7 Sn(SO4)2 + 7 SnCl4 + 4 Cr2(SO4)3 + 2 K2SO4 + 28 H2O
This is an oxidation-reduction (redox) reaction:
14 SnII - 28 e- → 14 SnIV (oxidation)
8 Cr13/2 + 28 e- → 8 CrIII (reduction)
SnCl2 is a reducing agent, KCr2O7 is an oxidizing agent.