Calculating E(cell) and Ratio of [Ni^2+]/[Zn^2+] in a Zn-Ni Cell

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SUMMARY

The discussion focuses on calculating the cell potential (E(cell)) for the electrochemical reaction Zn(s) + Ni2+(aq) → Ni(s) + Zn2+(aq) using the Nernst equation. The standard potential (Ecell) was determined to be 0.51V, and the Nernst equation was applied with concentrations [Ni2+] = 0.05M and [Zn2+] = 0.85M, resulting in an E(cell) calculation of 0.47V, which was noted to be incorrect as the expected value is 0.49V. The second part of the problem, which involves finding the ratio of [Ni2+]/[Zn2+], was also miscalculated due to the initial error in E(cell).

PREREQUISITES
  • Understanding of the Nernst equation and its application in electrochemistry.
  • Knowledge of standard electrode potentials for Zn and Ni half-reactions.
  • Familiarity with logarithmic calculations, specifically log base 10.
  • Basic principles of electrochemical cells and their reactions.
NEXT STEPS
  • Review the Nernst equation and its derivation for various electrochemical reactions.
  • Study standard electrode potentials for common half-reactions, particularly for Zn and Ni.
  • Practice calculating cell potentials with varying concentrations to reinforce understanding.
  • Explore the concept of equilibrium in electrochemical cells and how it affects cell potential.
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Students in chemistry or electrochemistry courses, educators teaching electrochemical concepts, and anyone involved in laboratory work related to electrochemical cells and their calculations.

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Homework Statement



For a cell in which the reaction Zn(s)+ Ni^2+(aq)->Ni(s)+ Zn^2+(aq) calculate the E(cell) when [Ni^2+]=0.05M, [Zn^2+]=0.85M.

Then, find the ratio of [Ni^2+]/[Zn^2+], when the cell is "flat"


Homework Equations



The simplified nernst equation ; E(cell)=E*(cell)-(0.0592V/n)xlogQ, log=log base 10

The Attempt at a Solution



Well I worked out the standard potential by adding half equations

Ecell=ENi-Ezn=0.51V

than because two electons are transferred, n in the nernst equation is 2.

Ecell= 0.51V-0.0592V/2log[0.85/0.05]

I plug that into my calculator, and I get 0.47V; the answer is 0.49V?
I tried doing the second part, and I got it wrong obviously, because I got the first part wrong
 
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I got 0.48V (0.477), it probably depends on values of standard potentials used and/or rounding errors.

But I don't see how the second part depends on the first, looks to me like these are completely separate problems.
 

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