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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: mystreet123 on May 17, 2016, 07:16:23 AM

Title: Concentration of ions in half-cell for measuring standard electrode potential
Post by: mystreet123 on May 17, 2016, 07:16:23 AM
Should we use 1moldm-3 or 2moldm-3 of H+ ion in the VO2(+)|VO(2+) half-cell? and why?

Thanks in advance!
Title: Re: Concentration of ions in half-cell for measuring standard electrode potential
Post by: Hunter2 on May 17, 2016, 07:32:21 AM
Please write the Nernst equation for this case.
Title: Re: Concentration of ions in half-cell for measuring standard electrode potential
Post by: mystreet123 on May 17, 2016, 07:40:29 AM
Quote from: Hunter2 on May 17, 2016, 07:32:21 AM
Please write the Nernst equation for this case.

We didn't learn this in high school...
Title: Re: Concentration of ions in half-cell for measuring standard electrode potential
Post by: Hunter2 on May 17, 2016, 07:48:10 AM
Check here:

http://www.chemguide.co.uk/inorganic/transition/vanadium.html
Title: Re: Concentration of ions in half-cell for measuring standard electrode potential
Post by: Hunter2 on May 17, 2016, 08:36:06 AM
The Nernst equation is:

E = E0 + 0,059 V/1 * (cVO2+ *c2H+)/cVO2+

If E = E0 = 1 V what has to be the concentration of each component.
Title: Re: Concentration of ions in half-cell for measuring standard electrode potential
Post by: Borek on May 17, 2016, 09:49:06 AM
Nernst equation doesn't matter.

What is the definition of "standard electrode potential"? What is "standard" about?
Title: Re: Concentration of ions in half-cell for measuring standard electrode potential
Post by: mystreet123 on May 17, 2016, 10:05:03 AM
Quote from: Borek on May 17, 2016, 09:49:06 AM
Nernst equation doesn't matter.

What is the definition of "standard electrode potential"? What is "standard" about?

I know the standard condition means the components have to be in 1 moldm-3 but I thought as the vanadium ion used is already 1moldm-3, 2moldm-3 of H+ should be used to fit the equation above...
Title: Re: Concentration of ions in half-cell for measuring standard electrode potential
Post by: Borek on May 17, 2016, 02:00:37 PM
Quote from: mystreet123 on May 17, 2016, 10:05:03 AM
I know the standard condition means the components have to be in 1 moldm-3

And that's all that matters - all substances present must have their concentrations (or more precisely: activities) equal to 1. Doesn't matter what the reaction is.
Title: Re: Concentration of ions in half-cell for measuring standard electrode potential
Post by: mystreet123 on May 18, 2016, 03:34:44 AM
Quote from: Borek on May 17, 2016, 02:00:37 PM
Quote from: mystreet123 on May 17, 2016, 10:05:03 AM
I know the standard condition means the components have to be in 1 moldm-3

And that's all that matters - all substances present must have their concentrations (or more precisely: activities) equal to 1. Doesn't matter what the reaction is.

How about Al3+(aq)|Al(s) half-cell? Can I use 0.5moldm-3 Al2(S04)3 but it also means SO4 2- ions are in 1.5moldm-3 concentration?
Title: Re: Concentration of ions in half-cell for measuring standard electrode potential
Post by: Hunter2 on May 18, 2016, 04:20:53 AM
I think so. The Sulfate doesn't take place in the reaction.