Moderators: Chem_Mod, Chem_Admin

Ryan Chang 1C
Posts: 105
Joined: Sat Aug 24, 2019 12:17 am


Postby Ryan Chang 1C » Sat Feb 22, 2020 12:59 pm

Calculate Ecell for each of the following concentration cells:
(b) Pt(s)|H2(g, 1 bar)|H1(aq, pH 5 4.0)||H1(aq, pH 5 3.0)|H2(g, 1 bar)|Pt(s)

When I wrote the half reactions, I got (2H+) + (2e-) -> H2 and H2 -> (2H+) + (2e-)
I would assume that n=2 based on the half reactions, but the answer key says that n=1. Why is that?

Posts: 19154
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 824 times

Re: 6N.7b

Postby Chem_Mod » Sun Feb 23, 2020 10:38 pm

In the answer key, they simplified the reaction to H+ (pH 3) --> H+ (pH 4). This is because H2 (g) is on the reactants and products side and can be cancelled out, and the rest of the reaction can be halved. This results in only 1 electron being transferred. You can also just keep your redox reaction as is--n will be 2 and the value of Q will be different--but you will still get to the same answer.

Hailey Kim 4G
Posts: 110
Joined: Sat Jul 20, 2019 12:16 am

Re: 6N.7b

Postby Hailey Kim 4G » Tue Feb 25, 2020 2:28 pm

If you use n=2, make sure you square the concentrations of your products and reactants for your value of Q (due to the coefficient of 2 in the H+). E should equal 0.06 V.

Return to “Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)”

Who is online

Users browsing this forum: No registered users and 3 guests