CHEMISTRY · Multi-part · AP · Chemistry · Acids and Bases · Acids and Bases
Problem
Zinc sulfide, ZnS(s), is placed in 1.00 L of water at 25 °C. The solubility product constant is Ksp=2.0×10−25. The first and second acid-dissociation constants of hydrogen sulfide are Ka1=9.1×10−8 and Ka2=1.3×10−13, respectively.
(a) A chemist must dissolve 0.0150 mol of ZnS completely in the 1.00 L sample. Derive an algebraic relationship that links the concentrations of all aqueous species to the equilibrium constants given.
(b) Calculate the minimum hydrogen-ion concentration required to dissolve the entire 0.0150 mol of ZnS. Report both [H+] and the corresponding pH.
(c) Concentrated HCl is supplied at 12.0 M. Determine the least volume (in millilitres) of this acid that must be added to reach the [H+] calculated in part (b), assuming the solution volume change is negligible.
(d) If instead the solution is buffered at pH 4.00, calculate the maximum mass (in grams) of ZnS that could remain completely dissolved in the 1.00 L sample at 25 °C.