Given that the K sp for CaF2 at 25°C is 3.9 × 10–11, will a precipitate form when 0.10 L of 2.3 × 10–4 M CaCl2 is added to 0.50 L of 5.0 × 10–3 M NaF? Assume volumes are additive.

Question

Given that the K sp for CaF2 at 25°C is 3.9 × 10–11, will a precipitate form when 0.10 L of 2.3 × 10–4 M CaCl2 is added to 0.50 L of 5.0 × 10–3 M NaF? Assume volumes are additive.
Please help me  I have no clue where to start.

Thanks!

DrBob222 · Answer

Calculate concentration of CaCl2 and NaF. Total volume is 0.1L + 0.5L = 0.6 L. Each salt is diluted from the initial volume to the final volume.
(CaCl2) = 2.3E-4 M x (0.1L/0.6L) = ?
(NaF) = 5E-3 x (0.5/0.6) = ?

Calculate Qsp = (Ca^2+)(F^-)^2 and plug in the values from above.
Compare Qsp with Ksp. If Qsp>Ksp a ppt forms. If Qsp<Ksp a ppt will not form.

Post your work if you get stuck.