The pH of of my Kalkwasswer is 12.5. Is it fully saturated?

[Mono]

Can the pH of a Kalkwasswer solution tell you it's degree of saturation?

(I know, a dumb question. And I'll probably feel embarassed when I read the answer and realize how dumb a question it was.)

 

[Dkeller_nc]

In theory, yes. In practice, no. That's because the pH scale is logarithmic, and very small changes in pH mean a rather large change in the hydronium ion concentration in the solution. The hydronium ion is H3O+, and is what actually exists in an aqueous solution rather than the H+ ion more commonly described in posts about pH.

However, you can accurately assess the saturation of a kalkwasser solution by conductivity. Here's a 2003 article by Randy that describes his measurements of the degradation of kalkwasser by conductivity.

 

[Randy Holmes-Farley]

With pH (crude for the reasons mentioned above, a 0.3 pH unit difference is 50% drop in saturation), I would measure truly saturated limewater (say, 2 teaspoons solids in a cup of RO/DI) and compare that to the fluid you are measuring.

 

[Mono]

Thank you very much gentlemen. I'm ok with a "rough estimate." I just plopped my nicely calibrated probe into the Kalk and it read 12.5. So, I guess that's somewhat useful information. It's better than a taste test and at least I'm not dosing RODI.