Question

K2Cr2O7 + SnCl2 + HCl --> CrCl3 + SnCl4 + KCl + H2O How many electrons are transferred?

Answer 1

Consider the half equations. We need to ignore spectator ions while balancing half equations. Spectator ions are those ions which undergo no change in oxidation number during a redox reaction.

Cr₂O₇^2- is reduced to Cr³⁺ while Sn²⁺ is oxidized to Sn⁴⁺. The half equations are

Oxidation: Sn²⁺ (aq) ----------> Sn⁴⁺ (aq) + 2 e^-

Reduction: Cr₂O₇^2- (aq) + 14 H⁺ (aq) + 6 e^- ---------> 2 Cr³⁺ (aq) + 7 H₂O (l)

In order to balance the number of electrons, we need to multiply the oxidation half by 3 and add to the reduction half. The balanced redox equation is

3 Sn²⁺ (aq) + Cr₂O₇^2- (aq) + 14 H⁺ (aq) -------> 3 Sn⁴⁺ (aq) + 2 Cr³⁺ (aq) + 7 H₂O (l)

The number of electrons transferred in the redox reaction is 6 (ans).