Answer:
0.0895 wt%
Explanation:
To treat a diffusive process in function of time and distance we need to solve 2nd Ficks Law. This a partial differential equation, with certain condition the solution looks like this:
[tex]\frac{C_{s}-C_{x}}{C_{s}-C{o}} =erf(x/2\sqrt{D*t})[/tex]
Where Cs is the concentration in the surface of the solid
Cx is the concentration at certain deep X
Co is the initial concentration of solute in the solid
and erf is the error function
First we need to solve the x/2sqrt(D*t) on the right to search the corresponding value later on a table.
[tex]\frac{2*10^{-3}m}{2*\sqrt{2.8*10^{-11}m^{2}/s*25h*3600s/h} } =0.6299[/tex]
We look on a table and we see for z=0.42 erf(z)=0.5525
Then we solve for Cx
[tex]C_{x}=C_{s}-(0.5525*(C_{s}-C_{o}))=(0.2-(0.5525*0.2))wt=0.0895wt[/tex]
Assuming Co=0
