SO2 gas and BrO3-

Sulfur dioxide gas is generated by reacting dilute hydrochloric acid with solid sodium sulfite.

2HCl(aq) + Na2SO3(s) →

SO2(g) + H2O(l) + 2NaCl(aq)

Is this reaction a redox reaction? Why/why not?

This reaction is not a redox reaction. Sulfur is in the +4 oxidation state in both SO3

2- and SO2.

2HCl(aq) + Na2SO3(s) → SO2(g) + H2O(l) + 2NaCl(aq)

This reaction is an acid-base reaction.

The SO2 tube is placed in a beaker of potassium bromate solution, which is colourless.

At this stage no SO2 is being produced.

As the SO2 begins to bubble through the solution, the bromate solution starts to change colour.

As SO2 continues to bubble through, the colour intensifies to a deep orange.

SO2 continues to bubble in, and the orange colour slowly fades.

The final solution is colourless.

Sulfur dioxide is a reducing agent (also known as an antioxidant in the food and beverage industries). It is oxidised to SO4

2-.

Bromine is in the +5 oxidation state in BrO3-.

It is reduced, first to Br2 (which is orange in dilute solution),

which is further reduced to colourless Br-.

Br-Br2BrO3

-

SO2(g) + 2H2O(l) → SO42-(aq) + 4H+(aq) +

2e-

2BrO3-(aq) + 12H+(aq) + 10e- → Br2(aq) + 6H2O

5SO2 + 4H2O + 2BrO3- → 5SO4

2- + 8H+ + Br2

Br2(aq) + 2e- → 2Br-

Br2 + SO2 + 2H2O → 2Br- + SO42- + 4H+

SO2(g) + 2H2O(l) → SO42-(aq) + 4H+(aq) +

2e-

Potassium bromate and potassium iodate are important oxidising agents because they are available in very pure form.

In most reactions involving bromate or iodate it is necessary to add acid.

2BrO3-(aq) + 12H+(aq) + 10e- → Br2(aq) + 6H2O