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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: kdbmvp on April 12, 2019, 07:57:23 AM

Title: Calculate concentration ratio
Post by: kdbmvp on April 12, 2019, 07:57:23 AM

Hello,

If we have the half-reactions:

Fe³⁺+e^- -> Fe²⁺
and
2H⁺ + 2e^- -> H₂

Calculate the ratio [Fe³⁺] / [Fe²⁺] at pH 2. Any hint? I was immediately thinking standard electrode potentials as we have two half reactions, but not sure exactly how to go on..

Title: Re: Calculate concentration ratio
Post by: kdbmvp on April 13, 2019, 03:20:52 AM

Anyone?

Title: Re: Calculate concentration ratio
Post by: isears on April 14, 2019, 11:09:48 AM

I think you're going to need the Nernst equation for this. The Nernst equation relates standard electrode potentials and Q, which is a function of the concentrations, to include the concentration of H⁺, which will eventually finally yield pH if you take -log.

Check out this khan academy vid!

https://www.khanacademy.org/test-prep/mcat/physical-processes/intro-electrochemistry-mcat/v/nerst-equation-edited