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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: maakii on June 15, 2007, 04:06:06 AM

Title: Potentiometric titration
Post by: maakii on June 15, 2007, 04:06:06 AM

Hey everyone,

I was doing a redox question on potentiometric titration when I realised that it was quite hard to answer without any knowledge of potentiometric titrations..

For one question, we have a solution of Sn²⁺ being oxidised by Fe³⁺ to give Sn⁴⁺ and Fe²⁺ using lets say a saturated calomel electrode(SCE) as reference. There are a few things I wish to know..

1)If we are connecting the reference electrode wth the Sn²⁺ half cell, then won't they react? Since E^o>0 for this pair of reference and indicator electrodes. But the answer says that it reacts with the Sn⁴⁺ produced.

2)What is at the equivalence point? It should have a sharp curve of voltage and is that when [Sn⁴⁺]>[Sn²⁺]?

Thanks a lot!

Title: Re: Potentiometric titration
Post by: DevaDevil on June 17, 2007, 02:00:25 PM

ok, let me get this straight: You have a single compartment cell with a Pt electrode and a SCE reference?
Or a double compartment with the Iron/Tin couple in one and the calomel in the other, connected by a salt bridge?

And:

Quote

1)If we are connecting the reference electrode wth the Sn2+ half cell, then won't they react? Since Eo>0 for this pair of reference and indicator electrodes. But the answer says that it reacts with the Sn4+ produced.

this is unclear to me. "they" won't react? and "it" reacts? What are those referring to?


The equivalence point is observed when all the Sn²⁺ has been reacted to Sn⁴⁺. At that point the iron you keep adding will dominate the cell potential, as you cannot further reduce the Sn⁴⁺. So at the moment the potential you measure stops reflecting the Sn couple and changes into the value for the iron couple you have your equivalence point.