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Topic: Redox tritation curve  (Read 338 times)

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Redox tritation curve
« on: June 23, 2022, 09:02:56 AM »
Hi!!
I have a doubt about the titration curve of a redox reaction

I have as titrand  a 50ml solution of Cr3+ 0.02M and as titrant a Sn2+ 0.1M solution in HCl 1M

I know that E°(Cr3+/2+)=-0.40V while E°(Sn4+/2+) = 0.14V

I've calculated the potential E gpr phi=0.001 using thos formula
Phi<1

E=E°(Cr3+/2+) +RT/nF ln( 1-phi / phi)

I get E= -0.577V for phi=0.001

But the tritatipn curves I usually see have always positive vute for "E"

Can a negative value be possibile? Can the tritation occour anyway?
Thanksss!

Hunter2

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Re: Redox tritation curve
« Reply #1 on: June 23, 2022, 09:48:39 AM »
In this reaction chromium get reduced and tin oxidised. The opposit is not possible.

E = Eox- E red

Use for E the Nernst  equation and the concentration of both ions.

The value should be positive.

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Re: Redox tritation curve
« Reply #2 on: June 23, 2022, 10:05:44 AM »
In this reaction chromium get reduced and tin oxidised. The opposit is not possible.

E = Eox- E red

Use for E the Nernst  equation and the concentration of both ions.

The value should be positive.

You mean I have to calculatw E(Cr3+/2+ us8ng the nersy equation??

And do the same thing for Tin?

Because using the standard potential I have: -0.40 + 0.14 = negqtive value

Using the nernst equation will be ok?
Thanks v)

Hunter2

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Re: Redox tritation curve
« Reply #3 on: June 23, 2022, 10:16:10 AM »
No it's opposit 0,14V -(-0,4V) = 0,54 V for E0 if both have same concentration.

But you have to develop E = E0  + RT/zF ln cox/cred for both elements

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Re: Redox tritation curve
« Reply #4 on: June 23, 2022, 01:43:12 PM »
No it's opposit 0,14V -(-0,4V) = 0,54 V for E0 if both have same concentration.

But you have to develop E = E0  + RT/zF ln cox/cred for both elements

But if Cr3+ is reduced it means it's the catodhe  so the correct formula should be:

E cathode - E anode= E(Cr3+/2+) - E(Sn4+/2+)= -0.40 -(0.14)

The opposite!!...
« Last Edit: June 23, 2022, 05:30:25 PM by xshadow »

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Re: Redox tritation curve
« Reply #5 on: June 24, 2022, 05:19:59 AM »
In this reaction chromium get reduced and tin oxidised. The opposit is not possible.

E = Eox- E red

Use for E the Nernst  equation and the concentration of both ions.

The value should be positive.
Am I missing something? otherwise your equation should be E = E(red) - E(ox)

Hunter2

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Re: Redox tritation curve
« Reply #6 on: June 24, 2022, 05:38:46 AM »
You are right it is the opposit E = Ered- Eox

What means this reaction cannot take place. The opposit would be the case Chromium II will be oxidised by tin IV to chromium III and tin II.