A chemist must remove from a water sample that also contains

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

Problem

A chemist must remove

Pb^{2+}

from a water sample that also contains

Ca^{2+}

. Initially, the solution is 0.020 M in each cation and is at 25 °C. Solubility-product constants are

K_{sp}(Pb(OH)_2)=1.2\times10^{-15}

and

K_{sp}(Ca(OH)_2)=4.7\times10^{-6}

. The chemist chooses to add solid NaOH slowly while monitoring pH. (a) Calculate the minimum pH at which

Pb(OH)_2

just begins to form a solid in the solution. (b) At the pH you found in part (a), determine the percentage of

Ca^{2+}

that would precipitate, if any. Show all work. (c) Using your results, state whether selective removal of

Pb^{2+}

is feasible under these conditions and support your conclusion with quantitative evidence.