What you are referring to is the solubility equilibria, specifically the carbonic acid equilibrium,
Not sure what you mean by 'solubility equilibria'. The solubility of calcium carbonate is dictated by
-log[Ca++] - log[CO3--] >= pKs
where pKs = -log(Ks) = 8.45 (calcite, 20 °C)
...which certainly affects the pH of the solution.
The inequality is the same regardless of pH. What does change with pH is the proportion of total carbo, Ct, that is CO3--: [H2CO3] = f1(pH)*Ct, [HCO3-]=f2(pH)*Ct, [CO3--] = f3(pH)*Ct.
Defining r1 = 10^(pH-pK1), r2 = 10^(pH-pK2) where pK1 = 6.38 and pK2 = 10.38 are the two pKs for cabonic acid at 20°C and d = 1/(1 + r1 + r1*r2) then f1 = d, f2 = r1*f1 and f3 = r2*f2. Ct can be determined from the alkalinity, the original pH of the sample and the end point pH to which it is titrated in determining the alkalinity.
Thus water chemists prefer to think of pH as the 'master variable' i.e. everything else depends on it. You can ask the question 'what happens if I add x grams of calcium carbonate to a solution or what happens if I add acid?' and in some cases there may be a pH shift but in others there won't be. For example, if a water (typical surface water) is in equilibrium with limestone and atmospheric CO2 adding more limestone (chalk) will not cause a pH shift. Neither will adding acid. In the former case nothing happens. In the latter case some more limestone will dissolve and the water will become more alkaline but it is still in saturation WRT atmospheric CO2 and limestone. No pH change. But if you add enough acid to dissolve all the limestone then the pH will change. In solving problems like this the approach is to write out all the equations and try pH values in them until you find the one that causes them to be consistent (electronic neutrality or proton condition). Hence the 'master variable' designation.
When you physically change the pH of the solution (not leave it at equilibrium state) by adding other acids, which occurs in the mash, you drive the equilibrium and thus the solubility of the constituents of CaCO3 and other solutes (to more or less of a degree)
If you are trying to say that acid dissolves limestone
CaCO3 + 2H+ --> Ca++ + 2HCO3-
that is true but adding acid doesn't necessarily change the pH as noted above. And even if you change the pH the solubility is still governed by
-log[Ca++] - log[CO3--] >= pKs
One of the (many) problems with adding chalk to mash is that the system never really comes to equilibrium. If one drops a piece of limestone into 10 N hydrochloric acid then the reaction proceeds very quickly. If one drops a piece of limestone into water acidified to pH 5.2 it will take a very very long time for it to dissolve. Thus the addition of chalk to mash is unpredictable because by the time equilibrium would be reached we would be putting away our brew gear. One is better off using calcium hydroxide. In neither case can there be any pretense that any particular water profile has been emulated.
But as noted there should never be any reason to add carbonate or bicarbonate as mash water at pH 5.2 contains very little of it (6 % of the total carbo) not to mention that it doesn't taste very good.
What brewers are most interested in is the molar solubility or solubility product (Ksp; equilibrium constant).....the actual amount of moles of solute (brewing salts) per liter of solution (brewing liquor, or mash, or wort). This is also dependent upon pH of the solution.
What brewers are interested in is particular levels of ion concentration expressed in mg/L or mEq/L though there is no real reason why mmol/L couldn't be used. After all, mEq/L is practically speaking the same thing. It's just that in water chemistry and brewing we use mg/L and mEq/L (or, in North America, the ppm as CaCO3 = 0.02 mEq/L). Brewer's don't care a fig about solubility products though they care about knowing that the solubility of gypsum is about 2.4 grams per liter in cold water and less in warm. Unless they are doing the kind of calculations I alluded to earlier they would have no use for the Ksp of caclium carbonate (most spreadsheets and calculators do not contain this constant nor ask about pH) but it does appear in one of the 6 equations that must be simultaneously solved if pH is to be predicted in an equilibrium carbonaceous water. One would do this if one wanted to simulate a natural water. One cannot do this for the chalk added to mash situation as the math only predicts what would happen at equilibrium if equilibrium were reached and it isn't.
The other case where brewers should be concerned about a Ksp is for that of hyroxyl appatite which, by precipitating in the mash when the water is high in calcium reduces mash pH through the release of hydrogen ions. This can be a factor where pH is controlled with phosphoric acid and the hardness is high.
Now, calculate all this for the other brewing salts and the combined solution and its equilibrium state, and I'd say it's pretty complex. Luckily we don't have to do this every Saturday!
It's not really complex - it's easily done in a spreadsheet where the difficulties are more related to the bookkeeping aspects than the hairiness of the math or chemistry. Excel has a very powerful feature called the Solver which tries values for pH until balance is found.
There really isn't much point in doing all this each brew day though as the proper amount of bicarbonate in brewing water is 0. Getting proper chloride, sulfate, magnesium, calcium and sodium levels from the salts of strong acids and strong bases is trivially done with a simple spreadsheet that does not need to know anything about pH's or pK's.
You just have to use more. I have a 130 TA and don't have any trouble getting conversion with the addition of just a little CaCl2 (calcium chloride), and if I"m brewin' English I add some gypsum.. And dang, I just remembered I'm bring something very yellow this week and need some lactic acid I don't have... grrrrr... Roasted malts help the pH go low to some extent (depending upon other factors but usually) and when brewing blonde ale (Beirmuncher's Blonde is OMG!) there is no dark grain involved...
