Three 0.10 M aqueous solutions—Pb(NO3)2, SrCl2, and K2CrO4—are mixed in equal volumes in a beaker maintained at 25 °C. Two sparingly soluble lead-containing salts, PbCrO4 and PbCl2, could potentially precipitate. The tabulated molar solubility products at 25 °C are Ksp(PbCrO4) = 2.8×10−13 and Ksp(PbCl2) = 1.7×10−5.
(a) Calculate the initial ion concentrations immediately after mixing but before any precipitation occurs.
(b) Using the Ksp data, determine which lead-containing solid, if any, will precipitate first. Show all reasoning steps.
(c) Qualitatively discuss how the presence of Sr2+ affects the extent of precipitation for the lead salts, even though Sr2+ itself does not enter into either solid phase.
(d) Predict whether any additional precipitation would occur if the beaker were cooled to 0 °C, assuming the Ksp values remain unchanged while ion solubility in water generally decreases with temperature. Provide justification.