Question

The ks there is 1.0 l of 1.0 m HF solution. when SaF₂(s) precipitates form in this solution, how many grams of Ca(NO₃)₂ should be added to grow? (ksp of CaF₂ = 4.0 × 10⁻¹¹, ka of HF = 7.2 × 10⁻⁴)

Answer 1

To assess whether CaF₂ will precipitate upon adding NaF to a Ca(NO₃)₂ solution, calculate the ion product ([Ca²⁺][F¯]²) and compare it to the Ksp. The NaF concentration is high compared to Ca²⁺, suggesting a likely precipitation of CaF₂ based on Ksp values.

Step-by-step explanation:

To determine whether CaF₂ will precipitate when NaF is added to a Ca(NO₃)₂ solution, you must calculate the ion product of the concentration of Ca²⁺ and F¯ ions.

If this ion product exceeds the Ksp, precipitation will occur. For a solution where 0.10 M NaF is added to a 2.0 × 10⁻⁵ M solution of Ca(NO₃)₂, you would first determine the final concentrations of Ca²⁺ and F¯ in the new total volume.

The final concentration of Ca²⁺ is (128 mL × 2.0 × 10⁻⁵ M) / (130 mL), and the final concentration of F¯, contributed by NaF, is (2.0 mL × 0.10 M) / (130 mL). The new ion products are calculated and compared to the Ksp.

Practically, in this scenario, the student should be able to see that since NaF is present at a much higher concentration than the Ca²⁺, and the Ksp of CaF₂ is quite low, there is a high likelihood that the F¯ concentration will be sufficient to precipitate CaF₂ even after accounting for dilution.