I was just trying to see the effect of concentration on adsorption in solutions, i.e. I was trying to verify the Freundlich isotherm. I used oxalic acid and a batch of homemade activated charcoal (using this site).
First I prepared solutions of different concentrations. Then I added the activated charcoal, stirred it for 5 minutes and filtered the solution. When I titrated the filtrate using KMnO4, after calculating the concentration, I found that the concentration of the solution had been increased!
I tried the same process with different concentrations of oxalic acid solution and the result was the same. Can anyone tell me where did I go wrong?
Note: I used the same batch of activated charcoal in all the experiments. (Even then, how did the concentration of the solution increase? Shouldn't it be the same or lower than the initial concentration?)
For titrating oxalic acid, I heated the solution to about 60 degrees C.( After filtering the solution)