SO 2 gas and BrO 3 -. Sulfur dioxide gas is generated by reacting dilute hydrochloric acid with solid sodium sulfite. 2HCl(aq) + Na 2 SO 3 (s) → SO 2.

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Presentation transcript:

SO 2 gas and BrO 3 -

Sulfur dioxide gas is generated by reacting dilute hydrochloric acid with solid sodium sulfite. 2HCl(aq) + Na 2 SO 3 (s) → SO 2 (g) + H 2 O(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 SO 3 2- and SO 2. 2HCl(aq) + Na 2 SO 3 (s) → SO 2 (g) + H 2 O(l) + 2NaCl(aq) This reaction is an acid-base reaction.

The SO 2 tube is placed in a beaker of potassium bromate solution, which is colourless. At this stage no SO 2 is being produced.

As the SO 2 begins to bubble through the solution, the bromate solution starts to change colour.

As SO 2 continues to bubble through, the colour intensifies to a deep orange.

SO 2 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 SO Bromine is in the +5 oxidation state in BrO 3 -. It is reduced, first to Br 2 (which is orange in dilute solution), which is further reduced to colourless Br -. Br - Br 2 BrO 3 -

SO 2 (g) + 2H 2 O(l) → SO 4 2- (aq) + 4H + (aq) + 2e - 2BrO 3 - (aq) + 12H + (aq) + 10e - → Br 2 (aq) + 6H 2 O 5SO 2 + 4H 2 O + 2BrO 3 - → 5SO H + + Br 2 Br 2 (aq) + 2e - → 2Br - Br 2 + SO 2 + 2H 2 O → 2Br - + SO H + SO 2 (g) + 2H 2 O(l) → SO 4 2- (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. 2BrO 3 - (aq) + 12H + (aq) + 10e - → Br 2 (aq) + 6H 2 O