Question

Write out the balanced equation for the following Reduction Reactions (If there is one)

1. VO2^(+)+ Na2SO3

2.VO2^(+) + H2O

3. VO2^(+) + NaBr

4. VO2^(+) + NaNO2

5. VO2^(+) + H2C2O4

Answer 1

The question is incomplete as without values of redox potentials, the feasibility of the complete reduction reactions cannot be predicted.

However, we can still qualitatively balance the equations.

   (1)

Here vanadium (V) is reduced from an oxidation state of +5 to +3.

To balance the half-reaction in (1), we need to add water and electrons.

(2)

1. Now sodium sulfite, the sulfur is in an oxidation state of +4 and will be oxidised to sulfate with oxidation state of +6. The relevant half-reaction will be

   (3)

Since, there are 2 electrons involved in the oxidation half-reaction, we need to multiply the reduction half-reaction with 2,

   (4)

Now, we can add equations (3) and (4) to get the complete reaction

   (5)

Cancelling out the electrons, adding the spectator ions and rearranging, we obtain

(6)

2. This reaction of vanadate with water is not feasible as water cannot act as a reducing agent to reduce the vanadium from +5 to +3. In water at neutral pH, oxygen in water is at its optimal oxidation state, in that it is already at -2 and it can only undergo oxidation to oxygen gas, with oxidation state 0. This oxidation step is not feasible without external influence and change of pH. And as no more information is provided as to the conditions of the reaction, this reaction is not feasible.

3. In this case, the oxidation half reaction is

   (7)

Here, bromine is oxidized from oxidation state -1 to oxidation state of 0.

Adding equations (4) and (7) and re-arranging, we get the completed reaction,

   (8)

4. Nitrites can be oxidized to nitrates with oxidation state of nitrogen (N) going from +3 to +5. The oxidation half reaction then becomes,

(9)

Adding equations (4) and (9) and re-arranging, we get the completed reaction,

   (10)

5. Oxalic acid acts as the reducing agent and undergoes oxidation where the oxidation state of carbon (C) goes from +3 to +4. The oxidation half reaction is

   (11)

Again combining the reduction half reaction from equation (4) and the oxidation of oxalic acid from equation (11) and re-arranging, we get

   (12)

Once again, it must re-iterated that there can be no prediction as to the feasibility of the above balanced and completed reactions without further information about reduction potentials of the half-reactions.