Lab Report Nernst Equation Problem

[BI Duck]

Hello!!

So I am working on my IA lab reports x_x, and I had a problem relating to the Nernst Equation. E = E° - (RT/nF) ln Q

I was asked to investigate factours that affect a certain variable in a galvanic cell

I chose the concentration affecting the voltage of a whole galvanic cell; and my plan was to prepare solutions of AgNO3 and CuSO4 in 1M, 0.75M and 0.5 M; and measure the voltage of all the 9 diferent probabilities of the galvanic cell.

The problem is that in my lab, the room temperature was not 25°C, so I coulnd't establish a temperature of 298.3 K in my equation. (the room remperature and the solutions were at 22°C).

But when I tried to apply the data in the formula (as I understood it ) with the 1M against 1M of the compounds, Nersnt equation's "ln (Q)" cancelled the "RT/nF" part; so I got in the end that E = E° with any change in the temperature X_X (I am really sure I didn't acuatlly understand it well ¬¬).

My question is. If you prepare a solution of AgNO3 1M; the number of ions Ag+ and ions NO3- will also be 1M ?

Hope I am now screwing things up...

[Drake Glau]

Ideally yes they should equal.

But using this equation isn't really solving that question as much as it is solving how much voltage you can get from solutions A and B at X concentration O.o

And that's all I got. i'm confused where you're pulling data from. How did you find Q? The data booklet electrode potential values are at 25C also, not 22. Not sure if the 3C will have a huge effect or not though. Also how did they cancel? Since they are multiplied the only way for it to cancel was one of the two values was zero which doesn't make sense because I'm assuming something happened during the actual lab doing

Mind refreshing what R and F mean again please? =/

Edit: Wikipedia, forgot they were constants...

The only way your equation could have cancelled to E=E^o is if nothing happened. No electrons moved, no voltage made, nothing happened...

For the 1M:1M trial I see how you ended up with E=E^o and it'll happen 2 more times when your ratios=1. But for the other 6 you should get a better result. The reason you're getting the E=E^o is like since the constants that are used in the equation are also at an assumed 25C and standard conditions even though yours were not. This is something for the evaluation on the credibility of your results more than anything for those 3 specific trials where you get Q=1 because it just doesn't make any sense really

Edited February 25, 2011 by Drake Glau

[BI Duck]

Ideally yes they should equal.

But using this equation isn't really solving that question as much as it is solving how much voltage you can get from solutions A and B at X concentration O.o

And that's all I got. i'm confused where you're pulling data from. How did you find Q? The data booklet electrode potential values are at 25C also, not 22. Not sure if the 3C will have a huge effect or not though. Also how did they cancel? Since they are multiplied the only way for it to cancel was one of the two values was zero which doesn't make sense because I'm assuming something happened during the actual lab doing

Mind refreshing what R and F mean again please? =/

Edit: Wikipedia, forgot they were constants...

The only way your equation could have cancelled to E=E^o is if nothing happened. No electrons moved, no voltage made, nothing happened...

For the 1M:1M trial I see how you ended up with E=E^o and it'll happen 2 more times when your ratios=1. But for the other 6 you should get a better result. The reason you're getting the E=E^o is like since the constants that are used in the equation are also at an assumed 25C and standard conditions even though yours were not. This is something for the evaluation on the credibility of your results more than anything for those 3 specific trials where you get Q=1 because it just doesn't make any sense really

First, Temperature SHOULD change the voltages, even if it doesn't vary a lot.

Data comes from stoichiometry, and precisely I was asking if 1M of AgNO3 has 1 M of Ag+ ions dilutes, so that I could establish the value of Q x_x.

Data booklet gives the standard fem, but you need this in order to calculate my 1M:1M non ideal galvanic cells at 22°C

And correct me if I am mistaken, but aren't constants like R and F suitable for not only the ideal conditions? (ideal gases for example use the R constant even when the temperature is not 25°C)

And they cancel because IF 1M of AgNO3 has 1M of Ag+ ions, and 1 M of CuSO4 has 1M of ions CU, then you would calculate natural logarithm of 1 which is 0 (therefore cancelling the part I just said.), so there is not only one way to have a E° = E (and there IS an electron transfer)

I kno' that calculating the E of a 1M:1M galvanic cell doesn't really makes sense since I have the data in the data booklet, but my friends are investigating the temeprature as a factour of the voltage; and the voltage gets affected by it :B

[Drake Glau]

Yes 1M of AgNO3 should give you 1M of both ions since the reaction boils down to a 1:1 mole ratio.

Sorry if my post seemed to be in a really random and contradicting order, I was typing while thinking

Why are there different concentrations if they are testing the change in temperature...?

Anyway, I think there is something wrong with Q, either it's not 1M of the salt=1M of the ions or there's something else to it because anytime Q=1 then nothing affects E and that's just wrong =/

After more thinking. Your copper is forming Cu²⁺ and silver is going from Ag⁺ to Ag so for one mole of the copper to be used would be 1 half equation of CuSO4 and 2 AgNO3 because of the charge differences. With stoichiometry this would cause the Ag and NO3 ions to have double the concentration of the Cu and SO4 ions giving a 1:2 ratio for Q so Q would = 0.5 (for the 1M:1M thing, it'll change for the others of course).

I'm hoping that was right somewhere, it's late and that's all I can think about. I'm pretty sure the charge difference has something to do with it though and I'm fairly sure there is a problem with only Q...

Edited February 25, 2011 by Drake Glau