Question $2$:

A potential step experiment was carried out in a solution containing $0\mathrm{.}05M$ ferrocyanide

$([Fe(CN{)}_6{]}^{4-})$ dissolved in a solution containing a large excess of inert electrolyte. Care was

taken to ensure that there was no stirring of the solution during the experiment, which

means that the mass transport resistance was entirely due to diffusion. The potential was

stepped from a value where there was no reaction to a potential at which the $[Fe(CN{)}_6{]}^{4-}$

was completely oxidised to $[Fe(CN{)}_6{]}^{3-}$ at a Diffusion$-$controlled rate, and the following

currents were recorded:

i$.$ Make a sketch of a concentration profile of $[Fe(CN{)}_6{]}^{4-}$ as a function of distance away

from the electrode, at time $=0,0\mathrm{.}001s,0\mathrm{.}01s,0\mathrm{.}1s$ within the range of the

experiment. How will the profiles look at $2$ different diffusivities of $0\mathrm{.}00005$cm$2/$s and $0\mathrm{.}000005$cm$2/$s $($You need $2$

approximate graphical sketches, on graph paper$)?$

$[20]$

ii$.$ Given that the area of the electrode is $0\mathrm{.}3c{m}^2,$ calculate the diffusion coefficient of

$[Fe(CN{)}_6{]}^{4-}$ in the solution.