Question

Using a value of Ksp = 1.8 x 10-2 for the reaction PbCl2(s) Pb+2(aq) + 2Cl-(aq).

The concentration of the products yields a value of 2.1 x 10-2.

Select the TWO statements that are true.

a) Ions are recombining to form a solid precipitate.
b) The concentrations of Pb+2(aq) and Cl-(aq) are expected to decrease.
c) The concentrations of Pb+2(aq) and Cl-(aq) are expected to increase.
d) The concentration of PbCl2(s) is expected to increase.
e) It is not possible to have a system with Ksp > 1.8 x 10-2.

Answer 1

Option A and Option B

Step-by-step explanation:

The concentrations of Pb+2(aq) and Cl-(aq) are expected to decrease (because you have initially very high values of [Pb2+] and [Cl-], they should decrease so that you equilibrium is reestablished, so that Qsp = Ksp).

Solids aren't measured using concentrations but the AMOUNT of PbCl2(s) is expected to increase.

It IS possible to have a system with Ksp > 1.8 x 10^-2 -- if you increase the temperature, then solubility and Ksp are both increased. It is also possible to have a system with Qsp > Ksp (as is true in this case). However, if Qsp > Ksp, the system will shift so that reequilibrium is reestablished. Over time, Qsp will be come equal to Ksp.