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Topic: REDOX and Iodometry *delete me*  (Read 2216 times)

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Offline twomblyhero

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REDOX and Iodometry *delete me*
« on: June 18, 2014, 05:45:03 AM »
We completed a redox titration of Iodine (25cm3)
(formed from 1M Potassium Iodide (KI), 0.1M Potassium Iodate (KIO3) and excess Hydrochloric acid (KCl)


against Sodium thiosufate (Nas2O3)

It took 25.8cm3 of 0.1 M Nas2O3 to get rid of the formed Iodine.

The question asks:

Use the equation below to calculate the amount of iodide ions that reacts with each mole of iodate ions in aqueous solution

2S2O32- (aq)+ I2 (aq)   :rarrow:  2I- (aq) + S4O62-(aq)

and determine the concentration of iodide ions in moldm-3

I am not sure what this is asking me! Do I need to calculate how the Iodine is originally formed?
I am really stuck on this one! Please help.


« Last Edit: June 18, 2014, 08:07:23 AM by twomblyhero »

Offline Hunter2

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Re: REDOX and Iodometry *delete me*
« Reply #1 on: June 18, 2014, 06:39:41 AM »
They want to know how much iodide was in the solution.

You have a sample of Iodide it reacts with iodate to iodine. Develop here the equation as well. The iodine is titrated. So you can calculate back.

Offline twomblyhero

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Re: REDOX and Iodometry *delete me*
« Reply #2 on: June 18, 2014, 07:32:24 AM »
Thanks for your answer; i'm still unsure of what to do.

I know
5KI + KIO3 + 6HCL  :rarrow: 3H2O + 6KCl + 3I2

and the ratio of 2S2O32- (aq)+ I2 (aq) is 2:1 I can work out the concentration of I2 but then how do I work the rest out?

Any ideas folks?

Offline Hunter2

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Re: REDOX and Iodometry *delete me*
« Reply #3 on: June 18, 2014, 07:41:36 AM »
Simple mathematics. You see how much iodide creates iodine.  And youn see how much thiosulfate is used for Iodine. You have to calculate the relation Iodide Thiosulfate.

Offline twomblyhero

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Re: REDOX and Iodometry *delete me*
« Reply #4 on: June 18, 2014, 07:51:58 AM »
So 5 moles of Iodide ions (from KI) will react with 1 mole of Iodate ions (from KIO3)?

concentration= moles         =  5   x 25/1000 = 0.0002mols dm-3
                     _____         
                      volume       

....still stuck!

Offline Hunter2

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Re: REDOX and Iodometry *delete me*
« Reply #5 on: June 18, 2014, 09:09:12 AM »
5 mol iodide create 3 mole iodine.

2 mol  thiosulfate correspond to 1 mol iodine

how many mole iodide correspond to thiosulfate?

Offline twomblyhero

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Re: REDOX and Iodometry *delete me*
« Reply #6 on: June 18, 2014, 09:22:05 AM »
1?

Offline Hunter2

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Re: REDOX and Iodometry *delete me*
« Reply #7 on: June 18, 2014, 09:24:43 AM »
No it is 6 mol Thiosulfate correpond to 5 mol Iodide.

With his knowledge calculate how many mole 25.8 ml of 0,1 M thiosulfate is.  If you have this then you can calculate the content of iodide. This you have to get in relation to your 25 ml sample.

Offline twomblyhero

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Re: REDOX and Iodometry *delete me*
« Reply #8 on: June 18, 2014, 09:36:11 AM »
Thanks for you help, I understand the ratios now. Just got to do the calculations now.

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