## Chemistry: The Central Science (13th Edition)

$LaF_3$ $solubility$ $\approx 2 \times 10^{-13}M$
$Kps (LaF_3) = 2 \times 10^{-19}$ 1. Find the inital concentration of $F^-$ in the solution: $[F^-]_{(initial)} = [KF] = 0.01M$ 2. Write the Kps equation: $Kps = [La^{3+}][F^-]^3$ $LaF_3 solubility = x$ $La^{3+} solubility = x$ $F^- solubility = 3x$ 3. Find x: $2 \times 10^{-19} = [x][x + 0.01]^3$ *Since x has a very small value compared to 0.01: $2 \times 10^{-19} = [x][0.01]^3$ $2 \times 10^{-19} = [x][10^{-6}]$ $\frac{2 \times 10^{-19}}{10^{-6}} = x$ $x \approx 2 \times 10^{-13}M$