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REDOX titration, iodmetry HELP!

(sorry, no subscript or superscript)
We completed a redox titration of Iodine
(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.

Reply 1

SilverNight

Ahahahaha...I hate this type of question.

As I understand it, you have you work out the concentration of iodide ions in the beginning. This means the concentration of the potassium iodide.

The starting point for this would be to write the ionic equation for reaction 1 (Potassium iodide with potassium iodate) then work backwards using the information you have been given about sodium thiosulfate.

For all of these, working with ionic equation is much more easier so don't try and write out the whole equation. It is important that you balance the equation correctly.

It is better for you to figure it out yourself though, as this is a type of question which regularly comes up in the actual exam.

If you still can't do it, post again and I'll help you again ^^
Good luck!

Reply 2

twomblyhero

Thanks for you advice. I don't have an exam on this, just an assignment...i'll need to know it eventually at Uni though! I have posted my answer in another thread to be checked, it would be great if you could check it for me!