Please: Calculating the emf of a cell, how do I know if a cell is non standard?

Discussion in 'Chemistry' started by Cat_with_no_eyes, Oct 30, 2010.

  1. Cat_with_no_eyes Registered Senior Member

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    The question says:

    Calculate the standard e.m.f. of the cell at 298 K?

    1) Ni (s) | Ni 2+^ (aq)|| Sn 2+^ (aq), Sn 4+^ (aq) |pt

    .....

    Will I have to use the Nernst equation? The questi does not even state if its standard or non standard? do i ignore the 298 K??

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    Last edited: Oct 30, 2010
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  3. Green Destiny Banned Banned

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    Are you aware you have to calculate the reduction and oxidation? For instance, you would have \(E_0=E_{red}+E_{oxi}\) and will measure the voltage of the cell.
     
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  5. Cat_with_no_eyes Registered Senior Member

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    yes I know I need to calculate E cell which is E cathode - E anode

    I'm not entirely sure of the next steps I must take alltogether and how? Please could you guide me on this? thanks
     
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  7. Green Destiny Banned Banned

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    Well, this is never easy stuff - atleast I never found it very easy. I even had to look it up again: here is an example:

    \(Zn(s) + Fe^2+ -----> Zn^2+ + Fe(s)\)

    To calculate the cell voltage, you need to split the equation (hopefully your are aware of how to do this, which gives us:

    \(Zn(s) -----> Zn2+ + 2e\)
    \(Fe^2+ +2e -----> Fe(s)\)

    Which are the two half-reactions as we have gathered you know about. You need to know the potentials required, so

    \( Zn^2+ + 2e -----> Z^n\) where
    \(E_0 = -0.76V\)

    This equation needs to be reversed, so \(E_0\) will be reversed also.

    \(Zn(s) -----> Zn^2+ + 2e\)
    \(E_0 = +0.76V\)
    \(Fe^2+ +2e -----> Fe(s)\)
    \(E_0 = -0.41V\)

    You then add the two equations together.

    ps. this is just an example. You will need to work this out yourself.
     
  8. arfa brane call me arf Valued Senior Member

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    298K is a standard temperature so the question is about standard potentials. Pt is a standard "inert" electrode too--it doesn't get reduced or oxidized, but acts as a source or sink of electrons.

    Your answer might be found here
     
  9. Green Destiny Banned Banned

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    Yes, that's right. I've just explained that.
     
  10. arfa brane call me arf Valued Senior Member

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    The Wiki page I referenced has a link to a list of standard electrode potentials, which will probably also be useful. These are often located in Chemistry textbooks, in the chapters that cover electrochemistry.
     
  11. Green Destiny Banned Banned

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    Ah yes, that is helpful.
     

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