Homework Help: AP CHEMISTRY

Posted by DAN on Wednesday, April 11, 2012 at 5:57pm.

A solution is prepared in which a trace or small amount of Fe2+ is added to a much larger amount of solution in which the [OH-] is 1.0 x 10^-2 M. Some Fe(OH)2 precipitates. The value of Ksp for Fe(OH)2 = 8.0 x10^-10.

A. Assuming that the hydroxide is 1.0 x 10^-2 M, calculate the concentration of Fe2+ ions in the solution.

B. A battery is prepared using the above solution with an iron wire dipping into it as one half-cell. The other half-cell is the standard nickel electrode. Write the balanced net ionic equation for the cell reaction.

c. use the nerst equation to calculate the potential of the above cell.

I don't know how to do B & C
For (A) i got 8.0*10^-6M. if not please help
Thank You!

AP CHEMISTRY - DrBob222, Wednesday, April 11, 2012 at 6:10pm
A is right.
What values are you using for Eo Ni and Eo Fe? My best table for those is over 50 years old.
AP CHEMISTRY - DAN, Wednesday, April 11, 2012 at 6:14pm
For Ni its -0.28V
& for Fe its -.440V
Is it right?
AP CHEMISTRY - DrBob222, Wednesday, April 11, 2012 at 7:45pm
EFe = EoFe -(0.0592/2)log(Fe/Fe^2+)
Substitute 1 for Fe and 8E-6 for Fe^2+, solve for EFe. Then reverse the sign and the half equation and add to the Ni reduction equation.
Fe + Ni^2+ ==> Fe^2+(8E-6M) + Ni

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