# Homework Help: Help with redox equation.

1. Oct 6, 2012

### Themaster711

1. The problem statement, all variables and given/known data

C2H5OH(aq) + I3-(aq) → I-(aq) + CO2(g) + CHO2-(aq) + CHI3(aq)

2. Relevant equations

3. The attempt at a solution

I am stuck on how to get C to combine with I in CHI3. Thanks.

2. Oct 6, 2012

### Staff: Mentor

You mean in terms of oxidation numbers? Which is more electronegative - carbon, or iodine?

3. Oct 6, 2012

### Themaster711

I am trying to balance it in acidic solution. Sorry I forgot to add that. I do not know which is more electronegative. We haven't learned that.

4. Oct 6, 2012

### Staff: Mentor

Please elaborate then on what your problem is - I don't understand what you mean by "how to get C to combine with I". Show - step by step - how you approach the problem.

5. Oct 6, 2012

### AGNuke

To be able to solve the problems of redox balancing, you need to know at least two things:

1.) Some prefixed rules in determining the oxidation number of some select few elements.

2.) Oxidation states and most stable oxidation states of various elements.

If you know these two things, balancing is an easy affair.

6. Oct 6, 2012

### Themaster711

Most redox problems are easy... But this one is different. I solved every other one with no problem but I'm not sure how to do the half reactions for this one.

7. Oct 6, 2012

### AGNuke

Can you see the structure of CHI3 - Iodoform. You can then apply the rules you may have learned to determine the oxidation number on C.

8. Oct 6, 2012

### Themaster711

How should I split the half reactions?

9. Oct 6, 2012

### AGNuke

HINT: Both half reactions uses Ethanol at reactant side.

HINT: Can you break this question into two different redox reactions? I am pretty sure there are multiple redox reactions going on. (Why???)

Last edited: Oct 6, 2012
10. Oct 6, 2012

### Themaster711

Thank you. I'll try that.

11. Oct 7, 2012

### Staff: Mentor

AGNuke is right - this reaction can't be balanced in an unambiguous way.

12. Oct 7, 2012

### Themaster711

I tried splitting this into:
C2H5OH + I3- > CO2 +I-
C2H5OH + I3- > CHO2- + CHI3

That didn't work, so I tried:

C2H5OH + I3- > CO2 + CHI3
C2H5OH + I3- > CHO2- + I-

I also couldn't solve it like this. Could someone show me what my half-reactions should be and I am sure I can take it from there. Thanks

13. Oct 7, 2012

### AGNuke

CHO2- = Formate ion?

From what I tried, this equation can't be solved. I tried very hard but I can't solve it.

14. Oct 7, 2012

### Themaster711

So have I. I also believe it can't be solved but it's in my textbook. I don't know what else to do.

15. Oct 7, 2012

### AGNuke

Is this is written CHO2- or CHO2-?

16. Oct 7, 2012

### Staff: Mentor

It can't be balanced because it is in fact sum of two reactions, each can be balanced separately:

2C2H5OH + 9I3- -> 18I- + CO2 + 3CHI3 + 9H+

2C2H5OH + 8I3- -> 15I- + HCOO- + 3CHI3 + 8H+

Now, you can add them side by side:

4C2H5OH + 17I3- -> 33I- + CO2 + HCOO- + 6CHI3 + 17H+

Technically this is a balanced reaction, but this approach doesn't yield unique equation, as any linear combination of these reactions will still look balanced, for example:

136C2H5OH + 595I3- -> 1173I- + 51CO2 + 17HCOO- + 204CHI3 + 595H+

but no real mixture will follow this stoichiometry.

17. Oct 7, 2012

### AGNuke

Ah. Infinite solutions. I made a silly mistake in determining the equation no. 1. XD

18. Oct 7, 2012

### Themaster711

I will post the equation in a different format to avoid confusion:

C2H5OH(aq) + I3-(aq) → I-(aq) + CO2(g) + CHO2-(aq) + CHI3(aq)

19. Jan 2, 2013

### Jshua Monkoe

cleared Borek! Couldn't see this up