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April 18, 2015

April 18, 2015

Posted by **Stein** on Sunday, August 26, 2007 at 7:58pm.

Triiodide ions are generated in a solution by the following reaction in acidic solution.

IO3- (aq) + I- ----> I3-

Triiodie ion is determined by titration with a thiosulfate solution (Na2S2O3). The products are iodide ion and tetrathionate ion (S4O6 2+).

a. Balance the equation for the reaction of IO3- with I- ions.

b. Write and balance the equation for the reaction of S2O3 -2 with I3- in acidic solution.

c. A 25.00 mL sample of a .01000 M solution of KIO3 is reacted with excess KI. It requires 32.04 mL of Na2S2O3 to titrate the I3- ions present. What is the molarity of the Na2S2O3 solution?

d. how would you prepare 500.0 mL of the KIO3 solution in part c, using pure dry solid KIo3.

- Chemistry -
**DrBob222**, Sunday, August 26, 2007 at 8:59pmLet's do this bit by bit.

The IO3^-/I^- is an oxidation/reduction reaction. Do you know how to balance that type? The I in IO3^- has an oxidation state of +5 and the I^- is -1.

- Chemistry -
**Anonymous**, Monday, August 27, 2007 at 10:08amYes, I know you must use the half reaction method to balance the equation. I put a 2 as the coefficient of I- but I'm not sure how to divide the equation into two reactions since there are only 3 parts.

- Chemistry -
- Chemistry -
**DrBob222**, Monday, August 27, 2007 at 11:10amPersonally, I think using I3^- complicates a relatively easy equation to write. So let's use I2 and we can add I^- to it later if that's what the professor wants.

6H^+ + IO3^- + 5I^- ==> 3I2 + 3H2O Then the liberated I2 is titrated with thiosulfate in this reaction.

I2 + 2S2O3^-2 ==> S4O6^-2 + 2I^-

This gets part a and b EXCEPT if the prof wants I3^-, then just add I^- to make it work. For example, the iodate equation, replace 3I2 with 3I3^- and balance that by using 8I^- on the left instead of 5I^-. For the second one use 3I^- on the right and I3^- on the left.

For part c. calculate mols IO3^-, use the equation to convert to mols I2 and use the titration equation to convert to mols thiosulfate. Then L x M = mols. You have mols thiosulfate and L thioulfatre and you can calculate M thiosulfate.

For part d. remember M = mols/L. You want 0.01 mols in 1 L so you will need -.005 mols in 500 mL. grams = mols x molar mass.

- Chemistry -
**Anonymous**, Monday, August 27, 2007 at 6:24pmthank you so much!

- Chemistry -
- Chemistry -
**Anonymous**, Monday, August 27, 2007 at 6:59pmwait, i'm sorry, do i get the moles of IO3 by divinding 174.9 (molar mass of IO3) by 1196.16g (the mass of the IO3, hydrogen and I3 combined?) (the whole left side of the equation?)

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