[jay]

Hey, im having trouble with the below problem, i know which formulas must be used and understand how to calculate the ionic strength, which is equal to 0.25, but am stuck calculating the activity coefficient.

Problem : The permanganate ion activity in a
              0.05M KMnO4 solution is
              a)0.616
              b)0.066
              c)0.023
              d)0.31
              e)0.040

Any help would be great
                thanks

[Demotivator]

It would be nice if you provide the equation you're using to calculate activity coefficient. If it's the extended equation:

-Log(f) = [(0.51 x Z² x SQRoot(I)) / (1 + (3.29 x d x SQRoot(I))] - (0.1 x Z² x I)
Where: Z = the ionic charge, I = the ionic strength of the solution, d = the ionic radius in nanometres.
Then for a value of d = .35 (an educated guess for mno4-):
I get f = 0.73
activity = .73(.05M) = .036