Silver ions have long been known to have biocidal properties. The increasing use of silver for this purpose has led to greater silver concentrations in waste water, and there has been some concern about it. However, recent studies found that the silver was largely put back into the environment as Ag₂S. The solubility of this sulfide is 1.4 × 10⁻⁴ g/L.
(a) Estimate the K′_sp for Ag₂S. (See Table 18b in Appendix J.)
(b) How does the solubility of Ag₂S change as the pH decreases?

Data given in Table 18b

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TABLE 18B Modified K'sp Values* for Some Metal Sulfides at 25 °C Substance HgS (red) HgS (black) CuS PbS CdS SnS FeS K'sp 4 x 10-5 2 x 10-53 6 x 10-37 3 x 10-28 8 x 10-28 1 x 10-26 6 x 10-19