At three sparingly soluble salts are investigated under two different pH conditions

CHEMISTRY · Multi-part · AP · Chemistry · Acids and Bases · Acids and Bases

Problem

At 25 ∘C25\ ^\circ\text{C} three sparingly soluble salts are investigated under two different pH conditions. The salts and their equilibrium data are as follows: • CaF2\text{CaF}_2 Ksp=1.6×10−10K_{sp}=1.6\times10^{-10} Ka(HF)=6.6×10−4K_{a}(\text{HF})=6.6\times10^{-4} • AgCl\text{AgCl} Ksp=1.8×10−10K_{sp}=1.8\times10^{-10} • ZnS\text{ZnS} Ksp=2.0×10−25K_{sp}=2.0\times10^{-25} Ka(HS−)=1.0×10−7K_{a}(\text{HS}^-) =1.0\times10^{-7} For each salt, equal masses are separately added to 250 mL250\,\text{mL} of the following buffered media: (i) pH=2.00\text{pH}=2.00 and (ii) pH=12.00\text{pH}=12.00. Assume no volume change upon dissolution. (a) For each salt, calculate its equilibrium molar solubility in the pH=2.00\text{pH}=2.00 medium. (b) Repeat the calculations in part (a) for the pH=12.00\text{pH}=12.00 medium. (c) Using your results, construct two separate rankings (one for each pH) listing the salts from most to least soluble. (d) Identify any changes in the order of solubility between the two pH values and provide a detailed chemical explanation for the trend reversal or lack thereof.

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