Two sparingly soluble fluoride salts—strontium fluoride, SrF

CHEMISTRY · Multi-part · AP · Chemistry · Equilibrium · Equilibrium

Problem

Two sparingly soluble fluoride salts—strontium fluoride, SrF2_2, and barium fluoride, BaF2_2—are separately brought to equilibrium in both pure water and in 0.10  M0.10\;\text{M} NaF at 25 °C. KspK_{sp} values at 25 °C are: SrF2_2: 2.5×10−92.5\times10^{-9} BaF2_2: 1.5×10−61.5\times10^{-6} Assume that activity coefficients are unity and that the volume remains unchanged. (a) Derive an algebraic expression for the molar solubility ss of a generic salt MF2_2 in a solution that already contains a fluoride ion concentration F0F_0. (b) Use your expression to calculate the molar solubility of SrF2_2 in (i) pure water and (ii) 0.10  M0.10\;\text{M} NaF. (c) Repeat the calculations in part (b) for BaF2_2. (d) For each salt, compute the percentage decrease in solubility caused by the added fluoride ion. (e) Rank the two salts in order of magnitude of percent decrease and justify your ranking, referring explicitly to numerical results and the relationship between KspK_{sp} and common-ion concentration.

Related theory

Browse the problem library