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September 2, 2014

September 2, 2014

Posted by **fenerbahce** on Friday, July 20, 2012 at 10:02am.

1) Zn|Zn^+2 (1M)| Cu|Cu^+2 (1M)

okay so by looking at example this example

Calculate the emf (voltage) for the following reaction:

Zn(s) + Fe2+ → Zn2+ + Fe(s)

Write the 2 half reactions:

Zn(s) → Zn2+ + 2e

Fe2+ +2e → Fe(s)

look up the standard electrode potentials in the table above

Zn2+ + 2e → Zn Eo = -0.76V

This equation needs to be reversed, so the sign of Eo will also be reversed.

Zn(s) → Zn2+ + 2e Eo = +0.76V

Fe2+ +2e → Fe(s) Eo = -0.41V

Add the two equations together:

Zn(s) → Zn2+ + 2e Eo = +0.76V

Fe2+ + 2e → Fe(s) Eo = -0.41V

Zn(s) + Fe2+ → Zn2+ + Fe(s) Eocell = +0.76 + (-0.41) = +0.35V

I came up with the answer: 1.11

So am I on the right track?

AND ALSO VERY VERY IMPORTANT**

for the first one they more have 1 M

but for this question:

Cu|Cu^+2 (1M) Cu|Cu^+2(0.1 M)

see how one has 1M and the other 0.1M will that make a difference in the calculation thank you.

- chemistry -
**fenerbahce**, Friday, July 20, 2012 at 10:03amNOTE I calculates by using the above example

- chemistry -
**fenerbahce**, Friday, July 20, 2012 at 11:03am******HOW DO YOU CALCULATE THE REDUCTION POTENTIAL OF 1 M CuSO4 AND 0.1 M CuSO4?

NOTE: THE REDUCTION POTENTIAL OF 1M Zn(NO3)2 IS -0.76 V. I'M REALLY STUCK.

- chemistry -
**DrBob222**, Friday, July 20, 2012 at 10:39pmYou have done the Zn/Cu cell right. The Ecell = 0.35 v.

For the same element (Zn/Zn^2+) and (Zn/Zn^2+) but with the Zn^2+ different concentrations, it is

Ecell = Eocell -(0.0592/n)log(dil soln/concnd soln). Eocell is always 0 since we have th same element. n is fairly obvious and the dilute and concd solns are obvious. Substitute and solve for Ecell.

If you want to do them separately (calc E reduction potential for the 1M then E reduction potential for the 0.1M) you can use

E = EoCell - (0.0592/n)log(Cu/Cu^2+)

For 1M, you substitute 1 for Cu and 1 for Cu^2+, log 1 = 0 and Ehalf cell for 1 M is just Eo. For 0.1M, substitute 1 for Cu and 0.1 for Cu^2+ and Ehalf cell is E = 0.34 -(0.0592/2)log 0.1

E = 0.34 -(0.0296)(-1) = 0.34+0.0296 = about 0.37.

- chemistry -
**fenerbahce**, Sunday, July 22, 2012 at 1:09pmThank you very much..And I posted another question, the most important ones that I don't know how to do.

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