How Do You Calculate Expected Cell Voltage in Electrochemistry?

[leaf345]

Hey guys, I just did a lab on electrochem but we haven't started learning this in our lectures so I'm not too confident on it. One of the lab question asks us to calculate the expected cell voltage. From reading the textbook, this is what I did:
The reaction was 2Ag+ + Cu -> 2Ag + Cu2+
I added reduction potentials of Ag and Cu to get 0.46V for the standard voltage. Then I used the nersnt eq'n
E= 0.46 -(0.05915/n)*logQ
What I'm not sure about is...
We used 0.1 M AgNO3 and Cu(NO3)2, so would n be 2 or 0.2?
And would Q= [0.1 Cu2+][1]/[0.1 Ag+]^2*[1]=10?
Help would be appreciated!

 

[leaf345]

Also, we did another cell that is giving me trouble too.
One 1/2 cell was:
Ag electrode
0.1 M AgNO3 solution

The other was:
Pt electrode
0.1 M Fe2+ and 0.1 M Fe3+

I think the overall redox rx'n was Ag+ + Fe2+ --> Fe3+ + Ag
so I calculated the expected cell voltage. But I get a value that is opposite to the sign of the voltage we observed.
What I did was
E=Eo -(0.05915/n)*logQ
where Eo= 0.8-0.77 because that is the difference between the redox potentials of Ag and Fe.
n=1 electron
Q= [Fe3+]/[Fe2+]*[Ag+] = 0.1/(0.1*0.1)=10
so E= negative something

Am I doing this one correct?

 

[Blueshift5]

Hello,

It's great that you're taking the initiative to learn and apply electrochemistry in your lab work. As for your question, n in the Nernst equation represents the number of electrons exchanged in the reaction. In this case, since 2 Ag+ ions are reduced to 2 Ag atoms, n would be 2. Additionally, Q represents the reaction quotient, which is the ratio of the product concentrations to the reactant concentrations. In this case, since the concentrations of both Ag+ and Cu2+ are 0.1 M, Q would be 1. So, your calculations seem to be correct.

However, it's important to note that the Nernst equation is only applicable to cells at equilibrium. If your lab experiment was not performed under equilibrium conditions, then the calculated cell voltage may not accurately represent the expected value. I would recommend discussing this with your instructor to ensure that your calculations are valid.

Overall, it seems like you have a good understanding of the concepts and equations involved in electrochemistry. Keep up the good work and continue to ask questions and seek clarification when needed. Best of luck with your studies!