Why did a fellow Yahoo Ans. Member put this as the answer to my question. Is it correct - Ionic equations?

Question

MY QUESTION:

The equations are redox displacement reactions:

a) Bromine water is added to a solution of potassium iodide and the mixture is shaken.

MY ANS: Br (aq) + KI (aq) ---> KBr (aq) + I (s)

Br(aq) + I-(aq) ----> Br-(aq) + I(s)

Br is reduced, I is oxidised. But is this correct?

I had an answer:

a) Bromine is Br2(aq) and Iodine in solution is I3-, or I2(aq). Bromine will be reduced as iodine is oxidized to I2. Potassium is indeed a spectator ion. The typical "molecular equaiton".

Br2(aq) + 2KI(aq) --> 2KBr(aq) + I2(aq)

or the ionic equation

Br2(aq) + 3I- --> Br- + I3-

First of all i never knew there was such thing as I3- (is this correct). Second, shouldnt I2 be a gas and be in the ionic equation and not I3-? I am not having a go at the answerer as he is well respected and knows much more than me! I would just like some guidance and whether this is correct or not as it doesnt seem to be for me.

10 points for best answer. Thanks in advance!

Answer 1

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Answer 2

Iodine is fairly insoluble in water, but does dissolve in aqueous potassium iodide solution because it forms the (I3)- ion*.

However, it would be a very pedantic examiner or teacher who expected the iodine to be included in the equation in that exact form.

Iodine would not be liberated as a gas in this reaction, though, and will often, in fact, separate as a dark solid.

*N.B.  this is three iodines covalently bonded with a single negative charge.  I3- might be taken to mean one iodine with a 'three minus' charge - which is not the case.

Answer 3

I was the one who wrote your answer.  I can assure you and "just browsin" that I have some experience in chemistry.  Two degrees and 35 years of teaching experience.

First of all, a bottle of iodine will contain solid iodine, I2.  If warmed it will sublimate to I2(g), but it will crystallize back to the solid form when it cools.  

More at http://en.wikipedia.org/wiki/Iodine

... from which I quote:

"Iodine under standard conditions is a dark-purple/dark-brown solid."

Secondly in solution where there are also iodide ions, molecular iodine, which isn't very soluble in water,  will combine with an iodide ion to form the "triiodide ion", I3-.

More at http://en.wikipedia.org/wiki/Triiodide

... from which I quote:

"The molecular iodine reacts reversibly with the negative ion, creating the triiodide anion, I3−, which dissolves well in water."

Yes, we know that Wikipedia is not the most authoritative source, but it makes a good first place to look.  Google I3- or "triiodide ion".  You will get over 14,000 hits.

http://www.google.com/search?hl=en&safe=...

And a word for "just browsin".  I don't mind being second guessed, but please get your facts straight before making snide, offhand statements.

======== Follow up ========

Pendantic?   That could be considered a bit insulting.  I don't think so.  Certainly my AP chemistry students would be expected to know about the triiodide ion, I3^-.  And anyone who has every done the iodine clock reaction or ever tested for iodine in solution with starch should have been exposed to the triiodide ion.

If you go back to my original post, I wrote a  "molecular equation" in which I wrote iodine as I2(aq).  Nothing too exotic about that.  When asked to write an ionic equation, I wrote it as I3^- because that is the way that it actually exists, and that is the whole point of an ionic equation.

Answer 4

pretty sure I is -1 valence

first, balance the equation:

Br(aq) + 2KI(aq) --> K2Br(aq) + 2I(s)

Br=2+

K=1+

I=1-

Answer 5

These Yahoo!  Answer members are just people like you.  Some of them make errors, and some of them are just plain wrong.  That's why you got that answer.

Answer 6

for your info, there is such a thing as I3-, its iodide.

the above looks correct to me, honestly, you can trust it.

hope this helps! (:

Answer 7

The answer you got is correct. About twenty years ago, there was a focus story in Popular Science concerning the triiodide ion, I3-. The details elude me, but there is such a thing. And for this particular situation, the products include both iodine I2 in suspension and the triiodide ion I3- in solution.

Answer 8

If the answerer gave you I3-, you should have been sure it was correct as I doubt that it was "inventing"! Now knowing who it was, you should have clicked on his Avatar! He does GOOD for his askers!!

Br2 would act as Cl2

Chlorine reacts with iodide anion:

Cl2 (aq) + 2 I- (aq)  

I2 (aq) + 2 Cl- (aq)

Triiodide ion is formed:

I2 (aq) + I- (aq)  ->   I3- (aq)

24+ hrs later: In the future you should simple say something like "I had a response to a question that had I3- in the answer. Can someone help me understand this?" Leave your opinions about the answerer to yourself.

When you have had enough answers, you are the only one who can close the issue. I suggest you give the original answerer "Best answer" and choose one for this Q.

Not sure why the original answerer and I deserve a thumbs down, but so be it!

Answer 9

i have no idea . but nobodys perfect! i quess he was just rushinq .