Given: K_sp Values Are 2

Multiple Choice

Given: K_sp values are 2.32 × 10⁻⁹ for Ca(C₂O₄) and 2.5 × 10⁻²⁷ for La₂(C₂O₄) ₃; pK_a1 = 1.25 and pK_a2 = 3.81 for oxalic acid. If a solution contains 0.020M Ca²⁺ and 0.020M La³⁺, what concentration of HCl is needed to precipitate La₂(C₂O₄) ₃.9H₂O but not Ca(C₂O₄) .H₂O ?
The concentration of oxalic acid is 1.0 M.

A) 6.5 M
B) 9.7 M
C) 4.8 M
D) 2.9 M
E) 8.7 M