I have a problem with measuring $\mathrm{pH}$ in ferric oxalate solutions ($\sim 5~\text{to}~\pu{10 g L-1}$ $\ce{Fe},$ $\pu{0.8 M}$ oxalic acid, $\pu{25 °C}$). While I am sure about the $\mathrm{pH}$-meter device and buffer solutions ($4$ and $7$) and also the good function of my electrode (Sentek) in other solutions, the $\mathrm{pH}$ value does not stabilize at all in such a way that it continuously decreases as far as the pH becomes negative and eventually, under-ranged.

Is there any interference or any requirements for $\mathrm{pH}$ measurement in oxalate solution?

  • $\begingroup$ What is your $\ce{Fe^3+}$ source? $\endgroup$ – Mathew Mahindaratne May 27 '19 at 22:29
  • 1
    $\begingroup$ Can be interfering eventual draging out calcium ions from the electrode glass ? $\endgroup$ – Poutnik May 28 '19 at 5:25

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