In the reaction, As2S3+xNO−3+yH+⟶2AsSO4+zNO2+aS+2H2O Find the coeffieicnts x , y, z and a (Respectively)
10, 4, 10, 3
This is a very special case of redox reaction. Note that the given reaction involves two oxidations and one reduction.
a. Two oxidation half reactions are
i. As3+⟶AsO3−4
ii. S2−⟶S
First, balancing these two half reduction reactions:
i. 2As3++8H2O⟶AsO3−4+16H++4e−
ii. 3S2−⟶3S+6e−
Now add the two equations to get
2As3++3S2−+8H2O⟶AsO3−4+3S+16H++10e− ...(i)
b. Reduction half reaction :NO−3⟶NO2
Now let us balance the reduction half reaction and proceed as usual.
NO3 + 2H++1e− ⟶ NO2+H2O ...(ii)
Adding the two reactions (i) and 10×(ii), we get
As2S3+10NO−3+4H+⟶2AsO3−4+10NO2+3S+2H2O