The Ksp-Solubility Conundrum
Roy W. Clark, Judith M. Bonicamp · Journal of Chemical Education · 1998
The calculation of solubility from K sp values, and its converse have long been a part of general college chemistry textbooks. The agreement between actual solubility and simple calculations of solubility from K sp values has been questioned many times. Incomplete dissociation, hydrolysis reactions, complex ion formation, ion pair formation and activity coefficients conspire to make such calculations crude at best.The authors sought to find those cases of partly soluble substances for which simple calculations such as K sp =S 2, and K sp =4S 3 can realistically be used for computing solubility from K sp and the reverse calculation. Empirical solubility data are compared with solubilities calculated from reliable K sp values that have been adjusted for activity coefficients. A table of 18 substances is suggested for textbook use.