[Big-Daddy]

ii) Using these oxidation states, a balanced equation for the formation of ClO2 from HClO3.

What is the application of oxidation states here? Without knowing what the other products are how can I work out what the equation will look like? (I know the oxidation state of Cl is +4 in ClO₂, +5 in ClO₃^-, +7 in ClO₄^-, etc.)

For safety reasons, chlorine dioxide is usually generated where it is to be used. For pulp
bleaching, ClO2 is made by the partial reduction of NaClO3 under acidic conditions using a
variety of reducing agents, for example, sulfur dioxide.

(c) Write a balanced equation for the formation of ClO2 by this reaction, using sulfuric acid
for acidification (there is only one other product).

In the laboratory, ClO2 is produced by the reaction between NaClO3 and oxalic acid,
(COOH)2, again in the presence of sulfuric acid. This also generates CO2, which dilutes the
ClO2.

(d) Write a balanced equation for the formation of ClO2 by this reaction.

Can I predict in all these cases that the equation balanced will not involve anything from H2SO4? If that were the case then it's unclear why acidic conditions are needed at all ...

[Hunter2]

The H⁺ are used in these reactions from the sulfuric. The sulfate will not changed and is not necessary to mention in the equation.

Half reaction: HClO₃ + H⁺ + e^- => ClO₂ + H₂O

Now your work to get the Oxidation

[Big-Daddy]

The H⁺ are used in these reactions from the sulfuric. The sulfate will not changed and is not necessary to mention in the equation.

Half reaction: HClO₃ + H⁺ + e^- => ClO₂ + H₂O

Now your work to get the Oxidation

I have no idea what's involved in the oxidation reaction. That's why I wrote, I need to know the other products or reactants surely to even begin to write the balanced equation...

[Borek]

for example, sulfur dioxide

[Big-Daddy]

No you've got it wrong ...

Question 1 refers to "Using these oxidation states, a balanced equation for the formation of ClO2 from HClO3." Hunter1's post also refers to this formation. The question here is, once I write the half-equation for HClO3 into ClO2, what is the other half-equation and how should I know?

Question 2 has nothing to do with that. Question 2 is the formation of ClO2 from NaClO3. The questions then are 1) can I be confident that H2SO4 plays no role except providing H+, and 2) how do I know what SO2 is reduced into?

[Hunter2]

If you have HClO₃. What is the next oxidation number of chlorine and which compound is it?

[Dan]

Hint: Disproportionation

[Big-Daddy]

If you have HClO₃. What is the next oxidation number of chlorine and which compound is it?

Hint: Disproportionation

Ah ... so the other reaction just involves oxidation of HClO₃ to the next oxidation state of Cl.

If Cl is being reduced from +5 to +4 in the reaction we already wrote, then the other product will be HClO₄? So we write:

HClO₃ + H₂O -> HClO₄ + 2H⁺ + 2e^-

Then combining with HClO₃ + H⁺ + e^- -> ClO₂ + H2O, we get:

3HClO₃ -> HClO₄ + 2ClO₂ + H₂O. Thanks!

What about question 2? a) I be confident that H2SO4 plays no role except providing H+, and b) how do I know what SO2 is reduced into?

[Borek]

SO₂ is not reduced.

[Big-Daddy]

SO₂ is not reduced.

Oops sorry, into which SO2 is oxidized is what I meant. This is clear because we've already got the half-reaction:

ClO₃^- + 2H⁺ + e^- -> ClO₂ + H₂O

In which Cl is reduced from +5 to +4 oxidation state. So SO₂ must be oxidized. Into what, and how do we know?

[Hunter2]

Which oxidation states of sulfur do you know?

[Big-Daddy]

Which oxidation states of sulfur do you know?

Well it can't be H₂S or S as the charge would have gone from +4 to 0 or -2 which is a reduction. Thus it has to be either SO₄^2- or one of the various other sulphur ions. SO₄^2- is probably the best guess anyway.

With disproportionation, do I always write out two ionic equations (one reduction, one oxidation) and then combine them? And the same when a reducing agent or oxidizing agent is involved? (Sorry if this is basic, I'm a bit confused ATM)

[Hunter2]

Yes sulfate is correct. Redox reaction you develop oxidation and reduction reaction everytime seperate.

A disproportionation you have only if one element is involved. Like the Chlorine acid goes to chlorine dioxide and Perchlorine acid.