[ronmar5693]

Thanks for that.

Would it be possible for you to outline the calculation with SO4 please so that I am able to calculate ammonium sulphate solution pH in a practical way? It is for an agricultural application.

Do you have any opinion of the combined effect of bicarbonates and ammonium sulphate in water? Usually we predict resulting pH by ignoring everything but bicarb, and calculating effect of various added acids on bicarb equivalents per litre. I'm guessing this is too simplistic?

[Borek]

It is not a trivial thing to do manually, all I can suggest is using a specialized software.

See for example http://www.chembuddy.com/?left=Buffer-Maker&right=pH-calculator

[Brian Lin]

Is it possible use mass and charge balance to calculate pH accurately in this question too (instead of using ice charts)

[SO₄^2-] (initial)= [SO₄^2-] (final) +[HSO₄^2-] + [H2SO4] where you can assume [h2so4] to be negligible

[NH₄+] (initial)= [NH₄+] (final) + [NH₃]

[NH₄⁺] + [H⁺] = 2[SO₄^2-] + [HSO₄^1-] + [OH-]

[Borek]

Is it possible use mass and charge balance to calculate pH accurately in this question too (instead of using ice charts)

Sure, go ahead. I would love to see you solving manually a 6^th degree resulting polynomial. Even make it 5^th, neglecting H₂SO₄ as you (correctly) suggested.

[ronmar5693]

Thanks for ideas.

I have tried a complex solution pH calculator before and I found I couldn't work it- was too complex and more suited to preparation of buffer solutions in a lab than natural waters. Is this one user friendly enough in a kind of bucket chemistry approach?

Application is fertiliser solutions in agriculture with different borehole water starting alkalinity. Typically fertilisers are added at pretty low concentrations and resulting concentrations in fertigation water are mM or less. We usually use nitric, sulphuric, or phosphoric acid to reduce bicarb to 20-40ppm which generally gives acceptable pH. Usually the approach is to ignore anything but milliequivalents of bicarb, treat acids like H2SO4 as complete single H dissociation only, and work out a rough approximation. pH is usually in the right ballpark but never correct. I was wondering about the effect of ammonium and whether we should be trying to take account?

Or any different ideas about what might be throwing it off? Waters I am using typically have a fair bit of HCO3 which we do take account of but usually also some silicates which we do not. EC predictions we make are usually about right which makes me think we have most of the important ions involved.

[Borek]

For more complicated solutions you have programs like MINTEQ or PHREEQC (and some others). Last time I checked none of these was what I would call "user friendly". Hardly surprising, these calculations are not easy and require tons of parameters.

Ammonium ion is definitely one of important acids present in the solution.