What reactions will occur at the anodes and electrodes of two iron electrolytic cells: both with iron metal electrodes, one with an iron(II) sulphate electrolyte, the other with an iron(III) sulphate electrolyte?

I set up an experiment with both types of cells connected in series, which yielded the following qualitative data:

  • Both cathodes saw vigorous bubbling--to me implying hydrogen gas evolution.
  • Also, there appeared to be a darkish iron plating on the cathode, implying two reactions occurring here.
  • Some bubbling at anodes.
  • Large quantity of dark green precipitate formed in Iron(II) electrolyte, I would assume $\ce{Fe(H2O)4(OH)2}$ precipitate.
  • A deepening orange in iron(III) solution and a relatively small quantity of orange precipitate, I would assume $\ce{Fe(H2O)3(OH)3}$ precipitate.
  • pH of electrolytes remained constant (measured with a pH probe). Conductivity of iron(III) solution remained constant, whilst conductivity of iron(II) solution--which was almost 20 times higher--steadily fell.

It seems to me that similar things are happening at the respective cathodes of the iron(II) and iron(III) cells: both hydrogen gas and iron metal are evolving. The hydrogen gas evolution momentarily increases pH, pushing equilibrium of iron complexes towards the precipitates--thus keeping pH constant.

I'm less sure about the anodes. But I think iron is entering solution as Fe(II) and Fe(III), respectively, with some oxygen evolution.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.