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Topic: Oxidation Questions;;;HELP  (Read 8455 times)

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Oxidation Questions;;;HELP
« on: November 21, 2006, 04:40:36 PM »
Alright, so I need some help for these questions...
I got most of them, I just want to confirm it because these questions are pretty much variations of the basics we learned with the textbook. So no reference to anything at all.

You dont need to answer all quesitons if its time consuming. I dont want to scare people away. Even if you can answer one question i'll be happy.

THANKS for ALL help in advance
1) Use half reactions to explain whether or not you would, in an aluminum container, store a solution of zinc nitrate.

I said no, because it'll be a redox reaction and aluminum will take the place of zinc so the solution will no longer be zinc nitrate, but aluminum nitrate


2) Using the half rxn method, balance the following reaction which occurs in basic conditions

Ag(s) + CN- (aq) + O2 (g) > Ag(CN)2-(aq)


3)For the following situations, write balanced ionic and net ionic eqns to describe the situations. If it is a redox sitatuion, write oxidation and reduction half rxns. Refer to activity series and solubility guidelines if necessary.

a) Soln of Lead(II) nitrate is mixed with soln of potassium iodide

b) Liquid sodium chloride is electrolyzed

Electrolyzed means + H2O right?
c) Aqueous gold (III) chloride is stirred with cadmium rod

d) Zinc nitrate soln placed in solid silver cup


Offline Dan

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Re: Oxidation Questions;;;HELP
« Reply #1 on: November 21, 2006, 05:01:15 PM »
1) I agree

2) Please show attempt, as required by forum rules

3a) Please show attempt, as required by forum rules

Will there be a reaction? If so what could it be? (hint: solubility)

3b) No, electrolysis is when a voltage is applied accross the liquid or solution.

3c) Please show attempt, as required by forum rules

Will there be a reaction? If so what could it be?

3d) Please show attempt, as required by forum rules

Will there be a reaction? If so what could it be?
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Re: Oxidation Questions;;;HELP
« Reply #2 on: November 21, 2006, 05:41:02 PM »
For #1, how would I use the half reactions to explain it.
What exactly does it mean when something is oxidized / reduced, other than the loss/gain of electrons?


I tried all the other questions, honestly, but I doubt I did it right. Just now I found some of my mistakes, but I doubt I'd get the right answer anyways.
i.e for 3a the solubility
So since a precipitate will form, then a reaciton will occur. Even without looking at the solubility table, why wouldn't a reaction occur. Everything would just cancel out in the net ionic equation, is that why? And in the net ionic equation we would determine if it is redox or not, correct?

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Re: Oxidation Questions;;;HELP
« Reply #3 on: November 21, 2006, 05:49:14 PM »
Also, if we have a balanced equation and we break it down to half reactions, do we use the same co-efficients for the half reaction, or do we reduce them or do we just ignore the co efficients.

Eg. 3Ag2S + 2Al> 6Ag + Al2S3

Half Reactions:

- I have to break it down into net ionic eqation and then the numbers should balance right?
Ag+ (aq) + e- > Ag (s)
Al(s) > Al+3(aq) + 3e

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Re: Oxidation Questions;;;HELP
« Reply #4 on: November 21, 2006, 06:11:48 PM »
For #1, how would I use the half reactions to explain it.
What exactly does it mean when something is oxidized / reduced, other than the loss/gain of electrons?
In this context, that is all it really means.
Are you familiar with reduction potentials (sometimes called electrode potentials)?
Using the potentials of the half reactions, you can determine the potential of the (whole) reaction, and whether it will happen spontaneously or not.

Quote
I tried all the other questions, honestly, but I doubt I did it right. Just now I found some of my mistakes, but I doubt I'd get the right answer anyways.
By posting your own attempts, we can guide you to the answer by looking at how you are approaching the problem. Nobody here is likely to just give you the answer, we aren't meant to.

Quote
i.e for 3a the solubility
So since a precipitate will form, then a reaciton will occur. Even without looking at the solubility table, why wouldn't a reaction occur. Everything would just cancel out in the net ionic equation, is that why? And in the net ionic equation we would determine if it is redox or not, correct?
Exactly right,  if all the possible salts were soluble then there would be no net ionic equation, because as you rightly said, the terms would cancel if all the possible salts were soluble. You can see whether it will be redox or not by looking at your equation.

So,

What is the precipitate? Is it redox? What are the relavent chemical equations?

In your second consecutive post,

The half reactions you have written are correct like that. For the net ionic, you will have to balance it fully by scaling the half reactions' coefficients.
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Re: Oxidation Questions;;;HELP
« Reply #5 on: November 21, 2006, 08:45:05 PM »
Balancing this eqation under acidic conditions:

HBIO3 + Mn2+ > MnO4- + Bi3+

I got

Mn2+ + 7H+ + 3HBiO3 >> 3Br3+ + MnO4

Is that correct?
No wait,

I found a mistake in what I did..
Now I got
2Mn2+ + 9H+ + 5HBiO3 >> 5Bi3+ + 2MnO4- + 7H2O

But now I'm wondering, Why did my first (incorrect) answer still balance in terms of charges...even though it was wrong..
Can anyone confirm my answer for me as well?
« Last Edit: November 21, 2006, 08:52:59 PM by lankan_ice_405 »

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Re: Oxidation Questions;;;HELP
« Reply #6 on: November 21, 2006, 08:58:05 PM »
Yep, your answer is right, good job.

In your first attempt, your atoms didn't balance. You can balance charges without balancing atoms, and vice versa, but the equation is not fully balanced until both atoms and charges match on both sides.
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Re: Oxidation Questions;;;HELP
« Reply #7 on: November 22, 2006, 04:55:07 PM »
Another question, I have to balance Cu +H2SO4 -> CuSO4 + H2O + SO2
The thing is thoough that on the left I get S with a oxidation umber of 6...but on the right, there are 2 S's...one of them has a charge of 6 and the other a charge of 4.
How do I get around that?

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Re: Oxidation Questions;;;HELP
« Reply #8 on: November 22, 2006, 05:35:29 PM »
Go for the net ionic equation, then it will become clear.
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Re: Oxidation Questions;;;HELP
« Reply #9 on: November 22, 2006, 10:56:10 PM »
Thanks a LOT for all of your help. You've all be very helpful.

I'll be back though! A couple more months before the semester ends, and then Engineering Science at U of T next year =)

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