Item 17 A voltaic cell utilizes the following reaction: 2Fe3+( a q )+H2( g )?2Fe

Question

Item 17

A voltaic cell utilizes the following reaction:
2Fe3+(aq)+H2(g)?2Fe2+(aq)+2H+(aq).

Part A

What is the emf of this cell under standard conditions?

Express your answer using three significant figures.

0.771

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Correct

Part B

What is the emf for this cell when [Fe3+]= 3.40M , PH2= 0.92atm , [Fe2+]= 7.0

Item 17

A voltaic cell utilizes the following reaction:
2Fe3+(aq)+H2(g)?2Fe2+(aq)+2H+(aq).

Part A

What is the emf of this cell under standard conditions?

Express your answer using three significant figures.

0.771

SubmitMy AnswersGive Up

Correct

Part B

What is the emf for this cell when [Fe3+]= 3.40M , PH2= 0.92atm , [Fe2+]= 7.0

Explanation / Answer

Since your emf is .771 and you are using the equation E=E-RT/nFlnQ
R=8.31 (given)
T=20+273=293 (given in problem)
n=2 since your Fe is going from +6 to +4 and the difference in electrons is 2 (found)
F= 96500 (given)
To find Q you use products/reactants
pH=3.5 so to find H+ you use 10^-3.5
Q= (10^-3.5)^2 x (.0012)^2 / (1.67)^2
you can ignore PH2
Therefore,
E= .771-(8.31)(293)/(2)(96500)lnQ
E= 1.156V = 1.2V

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