Chemistry - equation problem

[JPC]

Homework Statement

1) ok , first we have a solution of :
MnO2, C6H5COO- , OH-

we add Hydrochloric acid, the following reactions happen :
OH- + H3O+ = H2O
C6H5COO- + H3O+ = C6H5COOH + H2O

ok , now we are told that if we put in more Hydrochloric acid than needed, CO2 gas escapes, a question asks me for the equations of the reactions that produce this CO2

I am just told these Acid/Base couples :
HCO3- / CO3-2
CO2, H2O / HCO3-

2) No, with the same solution, with Hydrochloric acid being introduced in about the right proportions, we add a solution of (2Na+ +SO3-2)
Here, another question asks me for the equation of the reaction between MnO2 and SO2,H20

Here i am just told these Red/Ox couples :
MnO2 / Mn+2
SO3-2 / SO2, H2O

The Reaction environment is acid

Homework Equations

The Attempt at a Solution

1)
the semi equations :
HCO3- = CO3-2 + H+
CO2 + H2O = HCO3- + H+C6H5COOH + H3O(+) = C6H5 + CO3-2 + 3H+ + H (cannot be H alone so * 2) :
2C6H5COOH + 2H3O(+) = 2C6H5 + 2CO3-2 + 6H+ + H2

then
CO3-2 + H+ = HCO3-
then
HCO3- + H+ = H2O + CO2

(here, I am really not sure of my equations,and the paper doesn't even tell me that H2 gas escapes)2) The semi equations :

MnO2 + 4H+ 2e- = Mn+2 + 2H2O

SO3-2 + 2H+ = SO2 + H2O (no e- in the reactions !, how can it be an Ox/red reaction then ?)

 

[nate808]

SO2 + H2O + 2e- = SO3-2 + 2H+

Overall reaction:
MnO2 + SO2 + 2H2O + 2H+ = Mn+2 + SO3-2 + 4H+ + 2e-

In this reaction, the MnO2 is acting as an oxidizing agent, while the SO2 is acting as a reducing agent. The overall reaction is an oxidation-reduction (redox) reaction.

 

[Blueshift5]

For the first problem, the equations you have written are mostly correct. However, the final equation should be:
HCO3- + H+ = H2O + CO2

This is because in the original problem, we are told that CO2 gas escapes when excess Hydrochloric acid is added. So, the final equation should show CO2 as a product.

For the second problem, you are correct that there are no electrons involved in the reaction between SO3-2 and H+. This is because this is not a redox reaction. The red/ox couples given in the problem are not relevant to this particular reaction. The equation for the reaction between MnO2 and SO2, H2O would be:
MnO2 + SO2 + 4H+ = Mn+2 + SO3-2 + 2H2O

This reaction is taking place in an acidic environment, so the H+ ions are needed to balance the charges on both sides of the equation. The SO2 gas is produced as a product, which is why it is important to have the correct proportions of H+ ions in the solution.