Chemical Forums
Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: sebmista on November 01, 2006, 12:28:37 PM
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Ok - I remember when I took this in general chemistry but for some reason now its kickin' my ass.. Here are some questions I would like some help on if you guys dont mind.
So.. Ecell follows the basic equation : Ecell = EnotCell - (.059/n) log(Keq) Correct? And this is for half reactions
The total Ecell = Eright - Eleft ..
Now I get confused when I have to pick which half reaction is the right and which one is the left?
Appart from this I'm working on a question that goes like this.
--Consider the titration of 25mL of 0.01M Sn2+ by 0.05M TI3+ in 1M HCl, using Pt saturated calomel electrodes to fin the end point..
a) Write a balanced titration reaction
b)Write the nernst equation for the two different half reactions occurring at the indicator electrode.
c) Calculate E at the following volumes of TI3+ 4.90, 5.00 and 5.10mL
To be honest I'm like a deer in headlights i have no clue what to do.. I dont even know what its asking.. I'm usually good at chemistry I just recieved an A on my most recent Analytical Chemistry exam.. I just need someone to please explaine these things and I can then probably carry myself from there, PLEASE *delete me*
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when dealing with the Nernst equation I normally like to use
delta G = delta G° + RT ln Q
if you know how to use that equation you just have to put in
delta G = -n F Ecell
delta G° = -n F Enotcell
and you get the Nernst equation and you should know which way to plug values in
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Ok, I think I figured out how to do this problem...
First of all theres not a right or left cell, theres a Reaction ---
--The two half reactions are --
Tl3+ + 2e- = Tl+
Sn4+ + 2e- = Sn2+
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Now we need to react Sn2+ with Tl3+ so we have to add the top half reaction and subtract the bottom half reaction.. and after we do that we get
Rxn
Sn2+ + Tl3+ = Sn4+ + Tl+
This is the answer to part (a)
Now for part (b) we just do the two half reaction cell potentials
Ept = 1.280 - (.059/2) log ([Tl+/Tl3+)
Ept = .130 - (.059/2) log ([Sn2+/Sn4+)
For part (c) we just then add the Moles to the reaction in part (a) and then use the equations in part (b) with the new concentrations to find E cell...
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that should do it