Redox Relapse

airheadan

We need to know what the products of KI + H2O in ionic form.

dextercioby

The reaction should be

[tex] 2KI+H_{2}O\rightleftharpoons K_{2}O+2HI [/tex]

which in ionic form

[tex] 2K^{+}+2I^{-}+H^{+}+OH^{-}\rightleftharpoons 2K^{+}+O^{2-}+2H^{+}+2I^{-} [/tex]

I don't see any redox here...

Daniel.

airheadan

THe labis on oxidation reduction. It says that ppt turns pink in the presence of hyrdroxide ions and the starch will turn black/blue in the presence of molecular iodine. We figured that this meant that in the equation that this meant in the products their will be a hydroxide ions and an I molecule. We thought that the answer you gave us was right but our teacher said that we were closer when we showed him KI + H2O--> OH + K + I2 + H

dextercioby

Yes,i didn't think of that option.There it is.Can u find the coefficients by accomplishing the electron transfer ?

[tex] aK^{+}+bI^{-}+cH^{+}+dOH^{-}\rightleftharpoons eK^{+}+fOH^{-}+gI_{2}+h H_{2}\uparrow [/tex]

Daniel.

airheadan

yeah we should be able to, um what are the a,b,c,d,e,f,g for?

dextercioby

Coefficents,like 1,2,1/2,3/2,3.

So who's getting oxidated and who's getting reduced...?

Daniel.

airheadan

umm I havent done it yet;P

dextercioby

It's not funny.If u haven't done redox reactions in school,why do you bother with this problem...?

Daniel.

DrMark

Me thinks something is a miss here. Was it hydroxide or peroxide ?

airheadan

it was hydroxide

DrMark

OK what is ppt ?

Borek

Short for precipitate.

dextercioby: no O(2-) in solution! NEVER!

airheadan: what exactly was in the solution (list everything)? What was the pink precipitate?

Best,
Borek
--
Chemical calculators for labs and education
http://www.chembuddy.com
BATE - pH calculations, titration curves
CASC - concentration conversions, solution preparation

airheadan

the ppt is phenalthailene...and the reaction is K + I + H2O --> KOH + I + H

GCT

Alright, I would imagine that this is a simple dissociation reaction, [tex]KI_{(s)}+H_2O \rightarrow K^{+}_{(aq)}+I^{-}_{(aq)} [/tex]

The starch test will not work without molecular iodide however, I2. You'll need both I2 and I-, for the iodine complex involving I3-.

DrMark

OK I'm highly dyslexic, but did you mean phenolphthalein ? There still is something a miss here (like what would oxidize the I^-).

GCT

potassium reacts with water??? Never actually encountered this before, I though it would be a spectator ion. I've read about this and it seems that KI is dissolved in water to provide I-, subsequently I2 is added to form I3-, which can form complexes with starch conterparts to form a colored solution.

I'm somewhat sensitive about the way some high schools deal with redox reactions as at times they are completely misleading and inaccurate. I've had a post in my forum a couple of months ago regarding a high school chemistry competition of which one of the answers provided turned out to be completely inaccurate. I couple of students decided to seek help online for references and quotes.