Determining the pH of a solution by knowing the weight of its components

[Marco Buonocore]

Probably a bit naive, but please consider that I only have grade 10 chemistry, and that was many years ago!

If I were to say that a solution was 7% potassium carbonate and the rest water, could I determine the pH based on that alone? Is there an online calculator of sorts for this sort of thing?

Thanks!

 

[Prof_Pixel]

I don't know that this will help you, but it will give you an idea of the complexity of what you are asking: http://chemwiki.ucdavis.edu/Physica...s/Buffers/Henderson-Hasselbalch_Approximation

 

[Marco Buonocore]

I don't know that this will help you, but it will give you an idea of the complexity of what you are asking: http://chemwiki.ucdavis.edu/Physica...s/Buffers/Henderson-Hasselbalch_Approximation

Thanks for that link - it certainly puts things in perspective! I can tell when I'm in over in my head. On to plan B!

 

[Marco Buonocore]

I have access to a pH meter, which is great. The idea was to be able to get information from formulas without having to make them, do you follow? I guess for what I'm doing, it's not critical, so I won't pursue that line of thought any more. Thanks!

 

[Rudeofus]

Marco, I tried to pursue such a prediction tool at the initial stages of my venue into photo chemistry: it failed miserably. Poorly buffered solutions are extremely sensitive to minor environmental changes, and pH will be all over the place. Many solutions will also change pH over time, because aerial Carbon Dioxide would dissolve and lower pH, because some compounds oxidize and thereby change pH, or because somewhat volatile parts go away over time.

If you don't believe me: try to find a tool which correctly predicts pH of 1% Sodium Sulfite. There exists a range of online pH calculators, and since you have access to a pH meter, you can easily check which pH estimate works (hint: none will). None of the tools I found back then account for ionic strength phenomena, and the formulas which would account for ionic strength would rely on many constants which I was unable to find in published literature.

Your best bet is sticking to well established buffers if you want to reach some pH without a meter. Once you add extra stuff to these buffers (like other compounds found in photographic recipes), all bets are off.

 

[RalphLambrecht]

Probably a bit naive, but please consider that I only have grade 10 chemistry, and that was many years ago!

If I were to say that a solution was 7% potassium carbonate and the rest water, could I determine the pH based on that alone? Is there an online calculator of sorts for this sort of thing?

Thanks!

There is .Have you googled for 'ph calculator?:confused:

 

[RalphLambrecht]

Marco, if you have a relatively simple solution (eg. xg sodium carbonate anhydrous in a volume of water) it isn't too bad, and for some common substances there are some good online resources (carbonate for example). However once you add even one more compound it becomes difficult and gets far more complex as you continue to add things.

That's right;all the online calculators I've seen are limited to one compound,sorry

 

[Gerald C Koch]

For a simple solution of 1 or 2 components it is possible to describe the pH in closed form. You must know the pka value for each component. Once you get to more than 2 components you must resort to the method of successive approximations. This requires some programming and the use of a computer. The required computational time goes up exponentially with the number of components.

 

[sfaber17]

aqion.onl/show_ph is quite nice and does 3 components.

 

[Marco Buonocore]

Thank you Rudeofos for the buffer reference, and sfaber17 for the calculator - both very useful references. Just what I was looking for!