Ph calculator

RalphLambrecht · Jun 20, 2016

I once had but lost a link to a great ph calculator where you could select a chemical from a list such as boric acid plus any amount of water such as 100ml and it would give you the ph value,which I used to test my ph meter.Does anybody have a link like that?

JW PHOTO · Jun 20, 2016

RalphLambrecht said:
I once had but lost a link to a great ph calculator where you could select a chemical from a list such as boric acid plus any amount of water such as 100ml and it would give you the ph value,which I used to test my ph meter.Does anybody have a link like that?

No help here, but I'd love to see that list too. Hope somebody comes up with it.

DarkroomExperimente · Jun 20, 2016

was it something like this?

http://www.wolframalpha.com/widget/...oncentration&showAssumptions=1&showWarnings=1

DarkroomExperimente · Jun 20, 2016

ok that one seems a little unpredictable...it choked on sodium carbonate and said sodium bicarbonate has a pH of 5.6 ?...

this seems to work http://www.endmemo.com/chem/phcal.php

here's another http://www.webqc.org/phsolver.php

and another http://www.sensorex.com/ph-calculator/

this one allows 3 chemicals in solution http://www.aqion.onl/

sfaber17 · Jun 20, 2016

I think the www.aqion.onl was what you were looking for, but it is quite difficult to predict pH to very good accuracy. aqion handles temp and activity coefficients but still is off on predicting a carbonate buffer by more than 0.1 unit. You can lookup NIST/NBS standard buffers and get the formulas. Then you need to watch out for CO2 absorption from air, especially for pH=10 carbonate/bicarbonate.

Rudeofus · Jun 20, 2016

I have tried to calculate pH with quite a few of these online pH calculators, and sadly, they won't get you anywhere near the real pH. BTDT. All these pH solvers reduce the ion equilibrium equations into a set of non-linear equations and calculate its solution. They do not account for ionic strength, and will therefore give wildly inaccurate results. Since it is very difficult to account for ionic strength, and requires knowledge of many constants which are nowhere to be found in publicly available literature, it is unlikely that a reliable pH calculator will ever exist.

And yes, just like I didn't believe a word I read about "can't calculate pH reliably with these" back then, many here won't believe me either. All these non-believers are encouraged to grab a pH meter and measure pH of some developer concentrate as they dilute it. In most cases, a pH increase will be observed until at some dilution pH will finally start to drop. No pH solver I am aware of will predict this type of behavior.

RalphLambrecht · Jun 20, 2016

DarkroomExperimente said:
was it something like this?

http://www.wolframalpha.com/widget/...oncentration&showAssumptions=1&showWarnings=1

similar but no chemical name was required;the compound was selected from a list.

RalphLambrecht · Jun 20, 2016

silveror0 said:
Google search of "ph calculators" came up with quite a few options:
http://www.sensorex.com/ph-calculator/
Hope this helps.

Yes,tried that;too many choices; none very good

RalphLambrecht · Jun 20, 2016

DarkroomExperimente said:
ok that one seems a little unpredictable...it choked on sodium carbonate and said sodium bicarbonate has a pH of 5.6 ?...

this seems to work http://www.endmemo.com/chem/phcal.php

here's another http://www.webqc.org/phsolver.php

and another http://www.sensorex.com/ph-calculator/

this one allows 3 chemicals in solution http://www.aqion.onl/

that was it!Thanks

sfaber17 · Jun 20, 2016

Rudeofus said:
In most cases, a pH increase will be observed until at some dilution pH will finally start to drop. No pH solver I am aware of will predict this type of behavior.

aqion does model changes due to ionic strength per activity coefficients with Debye-Huckle, but not sure if it can show an increase and then a drop. He is a German guy and did a good job IMO. I'll send him a note and see what he says about accuracy. He added some chemicals to his list for me before.

Alan Johnson · Jun 21, 2016

The usual test method is to make up or buy some buffer solutions, not to do calculations.

Rudeofus · Jun 21, 2016

sfaber17 said:
aqion does model changes due to ionic strength per activity coefficients with Debye-Huckle, but not sure if it can show an increase and then a drop. He is a German guy and did a good job IMO. I'll send him a note and see what he says about accuracy. He added some chemicals to his list for me before.

aqion seems to do the right thing with regard to ionic strength, but appears very limited in their selection of compounds. Except for stop bath and HCA I am unable to formulate a photographic bath with these compounds, and even for stop bath I'd have to improvise.

sfaber17 · Jun 21, 2016

It has more compounds than the others mentioned, but trying to model a developer is a lot to ask. Maybe we could request our usual compounds be added. It does have ascorbic acid/ascorbate now. Need HAS and CD-4

sfaber17 · Jun 24, 2016

According to the author, Harald, the sodium carbonate system forms sodium complexes which make it more complicated. The potassium salts do not, so if you model a .025 molal K2C03/KHCO3 system, curiously, you get the 10.01 pH assigned to the standard sodium buffer. I modeled the standard phosphate buffer .025 molal KH2PO4/Na2HPO4 and it predicted the correct pH of 6.86. Now maybe I can get him to add Borax and acid pthalates.

dpgoldenberg · Jun 25, 2016

In addition to the various complications mentioned above, there is a fundamental reason that these calculators are unlikely to be reliable. In order for a solution to have a predictable and stable pH, that is for it to be an effective pH buffer, it must contain both a weak acid and its conjugate weak base, with no more than about a ten-fold excess of one or the other. An example of such a pair is acetic acid and acetate. If a weak acid or base alone is dissolved in water, only a tiny amount of it is converted to the other form, which means that it won't be an effective buffer.

There are recipes for preparing well-behaved buffer pairs, including ones designed specifically for calibrating pH meters. But making these solutions requires an accurate balance, high-quality reagents and purified water. As others have suggested, it is much easier to buy calibration buffers.

David

kreeger · Jun 26, 2016

Ralph, have you ever come across something that shows the starting proper PH of fresh developers? Assuming distilled water was used to eliminate variations in tap water, it would seem this could be helpful for commonly used developer solutions? I started doing it for myself with my PH meter so i could monitor when perhaps a stock solution like Xtol or D-76 might be bad to eliminate the variables, and to measure PH of things I was making 1-shot like HC-110 Dil E or Rodinal 1:50. I have a Beckman Zeromatic IV I use in my darkroom for these things, and I use readily available PH buffer solutions for the calibration - I only wish good probes weren't so stupid expensive for these things.

Thanks for any insight on that.

Alan Johnson · Jun 26, 2016

For example, manufacturer's data sheet p2 gives developer pH:
http://www.ilfordphoto.com/Webfiles/200621612182416.pdf

kreeger · Jun 26, 2016

Alan, I have not seen this before, thanks for sharing. I wish all the manufacturers went to that level of detail - even given specific gravity (SG) readings. It's been years since I had a hydrometer in my hand !!!

sfaber17 · Jun 27, 2016

sfaber17 said:
Now maybe I can get him to add Borax and acid pthalates.

Actually the Borax was already there and also the phthalic acid in the full version. Maybe some posters should re-read the OP.
The point is to get a program to help make buffer solutions. This one does that well. One reason why you would want to is because the NBS solutions are rather dilute, and suppliers of buffers typically boost the concentration for better buffer capacity and less sensitivity to dissolved CO2. This program has the capability to accurately predict the pH at varied concentrations and temperatures in most cases. The NBS Borax solution was modeled correctly by the program at pH 9.17, and the KHphthalate buffer at ph 4.01. You could use it to make a phosphate pH 7.00 buffer, which is hard to find a recipe for. It can do some citrate buffers and has ascorbic acid/ascorbate also, but in the full version.

Hexavalent · Jun 28, 2016

RalphLambrecht said:
I once had but lost a link to a great ph calculator where you could select a chemical from a list such as boric acid plus any amount of water such as 100ml and it would give you the ph value,which I used to test my ph meter.Does anybody have a link like that?

Perhaps http://www.hyperquad.co.uk/hyss.htm

Ph calculator

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