Hi,

Did you run the experiments with or without oxygen ? If dissolved O2 was availbale (open system) the oxidation of Fe(II) consumes protons, and this increases pH, but the subsequent hydrolisis of Fe(III) then realeaes acidity, and lowers the pH (there is a long list of papers and textbooks where you can find these reactions). A pH of 2.85 is very typical of ferric solutions where Fe(III) is hydrolized and precipitating under various mineral forms (ferric hydroxide, ferrihydrite, etc...depending on the chemistry of your solutions).

I hope this can help,

Cheers

You'd better describe more clearly. Is it a stocking solution or diluted solution, or some else after reduction of ferric?

Hi Nidesh,

To above comments the following reaction might help you in understanding what's going on:

4 Fe(II) + O2 + 10 H2O = 4 Fe(III)(OH)3 + 8H(+)

Best,

Krzysztof

All the response are appreciated and your question need to be clear as it is diluted one or what, because value get differ as per your type of solution.

Dear Researchers

I got the answer from Swatantra Singh ·and Javier España very clearly. The drop in pH of ferrous and ferric solutions is mainly due to the complex formation reactions of Fe species.

Thank you for supporting me.

Nidheesh P V