Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: twomblyhero on June 18, 2014, 05:45:03 AM
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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.
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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.
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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?
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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.
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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
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volume
....still stuck!
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5 mol iodide create 3 mole iodine.
2 mol thiosulfate correspond to 1 mol iodine
how many mole iodide correspond to thiosulfate?
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1?
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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.
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Thanks for you help, I understand the ratios now. Just got to do the calculations now.