I have solution containing 18g/L V(X) + 4g/L Ni(II) and 4g/L Fe(III).
solution is acidic and contains about 0.02M of H2SO4. I expect that pH probe will show pH around 0.5, however this valu is observed for less then 2 minets. Next is it's growing fast to 11.
I assume it is the adsorption of ions V (III) or V (IV) or V (V) on the electrode. How to solve prolem and mesure pH constantly.
pH of 0.02M H2SO4 is about 1.6. Try to use 0.1 M sulfate buffer with pH 1.6
Well, the pH of pure sulfuric acid, in fact, should be about 1.6, unfortunately vanadate ions form vanadium acid, which significantly lowers the pH of the solution (probably).
My problem is the instability of a typical glass pH electrode which shows that the environment is alkaline. I tested two different electrodes with the same effect each time.
Of course, I tested the solution with universal straps. The pH is between 0 and 1.
There is no mistaking, the solution is acidic. Otherwise, the iron ions would precipitate in the form of hydroxide.
I always prefer to work in buffered solution. I guess that when you add vanadates into acidic media, they form polyoxovanadates via condensation reactions. Protons are consumed in this process. The increase of pH in synthesis of polyoxometalate is very common. Therefore, I advised you to use a buffered solution.
Thank you for your help. I also prefer to work in systems that are stable, especially if we talk about pH.
Thank you again.
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