Question

Calculate the Qsp or Ksp, as indicated, and determine whether a precipitate will form when each of the following mixtures is prepared. (You may assume temperature is held constant, volumes are additive, and that the initial solutions, prior to mixing, are unsaturated.)

25.24 mL 1.30×10⁻⁴ M CaCl₂ is mixed with 25.34 mL 3.32x10⁻³ M NaF. (Ksp for CaF₂ = 3.5×10⁻¹¹)
Qsp = ___

Answer 1

To determine if a precipitate will form when solutions of CaCl₂ and NaF are mixed, calculate the final concentration of Ca²⁺ and F⁻ ions in the mixed solution, then determine the reaction quotient (Qsp). If Qsp is greater than the solubility product constant (Ksp) for CaF₂, a precipitate will form.

Step-by-step explanation:

To calculate whether a precipitate will form when 25.24 mL of 1.30×10⁻⁴ M CaCl₂ is mixed with 25.34 mL of 3.32x10⁻³ M NaF, we need to determine the Qsp (Reaction Quotient) and compare it with Ksp (Solubility Product Constant) for CaF₂, which is given as 3.5×10⁻¹¹.

First, we calculate the final concentrations of Ca²⁺ and F⁻ ions after mixing. The concentration of Ca²⁺ will be the initial concentration of CaCl₂ (1.30×10⁻⁴ M) because chloride ions do not participate in the relevant equilibrium. Since the volumes of the two solutions are almost equal, we can approximate the final concentration of Ca²⁺ as half its initial value. Similarly, the concentration of fluoride ions will be half the initial concentration of NaF.

Thus, we have Ca²⁺ concentration of (1.30×10⁻⁴)/2 M and F⁻ concentration of (3.32×10⁻³)/2 M.

Next, we calculate the Qsp:
Qsp = [Ca²⁺][F⁻]²
Qsp = ((1.30×10⁻⁴)/2)((3.32×10⁻³)/2)²

Once we have the Qsp value, we compare it with the Ksp:
- If Qsp < Ksp, no precipitate will form.
- If Qsp > Ksp, a precipitate of CaF₂ will form.