When pH is Known

Many metal ions, in fact all but the alkali metal ions, form slightly soluble hydroxides. The concentration of [OH ], and hence the pH, required for 

Notice how the slopes vary with n. Many anions other than OH are Bronsted bases. Consider, for example, the solubility of CaC03 as a function of pH. 

When solid CaCOj is equilibrated with a buffered solution, how does its solubility vary with pH  

The variation of (the solubility) with pH can be easily plotted as a function of pH using the spreadsheet. First, label A1 as pH and B1 as log Ca- For A2 to A16, /EF /BF /F 0 to 14 in steps of 1. In cell B2, the formula for (K /a2) in spreadsheet format, which is +0.5 LOG (4.7E-9/(A2 2 + 10 -6.13 A2 + 10 6.13+10.33)). Then /EC(/BC /C from B2 to B2..B16. For the graph, use B2 to B16 as series 1, with A2 to A16 as the X series. A figure drawn from this spreadsheet shows that at pH values above pK2 of carbonic acid, the solubility is constant between pKj and pK2 where a2 decreases linearly with [H ] (slope of log 0L2 vs. pH is + 1) log C(3a increases by 0.5 for every unit decrease in pH at still lower pH values, log C a increases by 1 for every unit pH decreases. If the solution is acid rain at pH 4.0, the spreadsheet will help you find the solubility of a limestone statue (assume pure CaC03). 

When the pH of the solution is not given or when the pH of the solution is altered by the dissolution of the precipitate, the calculations cannot be carried out without the prior determination of the equilibrium pH. 

---