A chemical engineer must choose a calcium salt that will remain insoluble throughout…

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

Problem

A chemical engineer must choose a calcium salt that will remain insoluble throughout a production process in which the pH fluctuates between 3 and 11. Four candidate salts are listed below along with data for their conjugate acids.
SaltConjugate acidKaK_a of conjugate acid
CaCO3_3(s)H2CO3H_2CO_34.3×10−74.3\times10^{-7}
CaC2_2O4_4(s)HC2_2O4−_4^-5.6×10−55.6\times10^{-5}
CaSO3_3(s)HSO3−_3^-1.4×10−21.4\times10^{-2}
CaSO4_4(s)HSO4−_4^-1.0×10−21.0\times10^{-2} (stronger)
(a) Rank the four calcium salts in order of increasing sensitivity of their molar solubility to pH changes within the range 3 ≤ pH ≤ 11. Provide your ranking from least sensitive to most sensitive. (b) Using the numerical data, explain the reasoning that led to your ranking in part (a). Your answer should reference quantitative comparisons among the KaK_a values and any necessary qualitative deductions about the basicity of the anions. (c) Identify the salt that best meets the engineer’s requirement of remaining effectively insoluble across the stated pH range. Support your choice with a concise argument based on your analysis in parts (a) and (b).

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