Question

AsO2-(aq) + ClO-(aq) → AsO3-(aq) + Cl- (aq)

How do I balance this in basic conditions using half reactions?

Answer 1

at anode,
AsO2- --> AsO3-
for balancing O add H2O to reactant side
AsO2- + H2O --> AsO3-

for balancing H add 2H+ to product side
AsO2- + H2O --> AsO3- + 2H+

for balancing th charge add 2e- to reactant side
AsO2- + H2O + 2e- --> AsO3-

at cathode
ClO- --> Cl-
for balancing O add H2O to product side
ClO- --> Cl- + H2O

for balancing H add 2H+ to reactant side
ClO- + 2H+ --> Cl- + H2O

for balancing charge add 2e- to product side
ClO- + 2H+ --> Cl- + H2O + 2e-

now add anode and cathode reaction
we get
AsO2-(aq) + ClO-(aq) → AsO3-(aq) + Cl-AsO2-(aq) + ClO-(aq) → AsO3-(aq) + Cl-