Question

Balancing the following redox reaction in an acidic solution. How many electrons are transferred in this reaction? Cr2O7 2-(aq) + Cl- (aq)  Cr3+ (aq) Cl2 (g)

Answer 1

at anode
Cl- --> Cl2

for balancing Cl multiply Cl- cofficient by 2
2Cl- --> Cl2

for balancing charge add 2e- to product side
2Cl- --> Cl2 + 2e-

at cathode
Cr2O7-2 --> Cr+3

for balancing Cr multiply cofficient of Cr+3 by 2
Cr2O7-2 --> 2Cr+3

for balancing O add 7 H2O to product side
Cr2O7-2 --> 2Cr+3 + 7H2O

for balancing H add 14H+ to reactant side
Cr2O7-2 + 14H+ --> 2Cr+3 + 7H2O

for balancing charge add 6e- to reactant side
Cr2O7-2 + 14H+ + 6e- --> 2Cr+3 + 7H2O

now multiply anode reaction by 3 and add to cathode reaction
Cr2O7-2 + 14H+ + 6Cl- --> 3Cl2 + 2Cr+3 + 7H2O

so, total 6 electron transfer