Determining ion charge using rate constants and ionic strength

I am given the following data:



> 
> The rate constant $k$ at $\pu{25 ^\circ C}$ in a reaction of persulfate ions and iodide ions in a water solution is assumed to vary with the total ionic strength of the solution which follows:
> $$
> \begin{array}{l|cccccccc}
> \hline
> I/\pu{mol dm^-3} & 2.45 & 3.65 & 4.45 & 6.45 & 8.45 & 12.45 &\\
> \hline
> k/\pu{dm^3 mol^-1 s^-1} & 1.05 & 1.12 & 1.16 & 1.18 & 1.26 & 1.39 \\
> \hline
> \end{array}
> $$
> Determine the value of the product of the ion charges $(z\_Az\_B)$ for the two ions in the reaction.
> 
> 
> 


From previous problems I thought this would be a straight forward problem solved by using the equation:
$$\log k = \log k\_0 + 1.02z\_Az\_B(I)^\frac{1}{2}$$


So I plotted $\log k$ against $I^\frac{1}{2}$ and got that the slope is $0.0584$. This is not the correct answer, the correct slope should be around $2$ but how this slope is obtained is not given to us. I was wondering if anyone here sees what I am doing wrong? All help is appreciated!


