Question

Using the Nernst equation if needed and the original diluted [Pb2+] and [I^-] to calculate the [I^-] in solution.

Mixed 9 mL of 0.050 M KI solution with 3 mL of 0.050 M Pb(NO₃)₂.

Answer 1

Total volume = 12 mL = 0.012 L

Here, Initial concentration of I^- = 0.05 M

Initial volume of I^- = 9 mL

Initial concentration of Pb²⁺ = 0.05 M

Initial volume of Pb²⁺ = 3 mL

Therefore, concentration of the I^- in mixture = (0.05 x 9)/(12) = 0.0375 M

Concentration of Pb²⁺ in mixture = (0.05 x 3)/12 = 0.0125 M

We have, Ksp of PbI2 = 1.4x10^-8

Also, Q = [Pb²⁺][I^-]² = [0.0125][0.0375]² = 1.76 x 10^-5

Since, Q >> Ksp precipitate will be formed and Pb²⁺ will be consumed.

Therefore,

Concentration I^- left in the solution = 0.0375 – [(2 x 0.0125)] = 0.0125 M