Question

For parts of the free-response question that require calculations, clearly show the method used and the steps involved in arriving at your answers. You must show your work to receive credit for your answer. Examples and equations may be included in your answers where appropriate.

Pbl₂(s) ⇄ Pb2²⁺ (aq) + 21⁻ (aq) Ksp=7x10⁻⁹

The dissolution of Pbl₂(s) is represented above.

(a) Write a mathematical expression that can be used to determine the value of S, the molar solubility of Pb1₂(s). (Do not do any numerical calculations.)

Answer 1

The mathematical expression to determine the value of S, the molar solubility of PbI₂(s), is Ksp = S(2S)², which takes into account that the concentration of I⁺ ions is twice that of Pb²⁺ ions in a saturated solution.

Step-by-step explanation:

To write a mathematical expression that determines the value of S, the molar solubility of PbI₂(s), you would start by setting up the equilibrium expression based on the solubility product constant (Ksp) for the dissolution of PbI₂(s).

Given the dissolution equation PbI₂(s) ⇄ Pb²⁺ (aq) + 2I⁺ (aq), the expression for its solubility product constant, Ksp, would be Ksp = [Pb²⁺][I⁺]². The molar solubility S would then represent the concentration of Pb²⁺ in a saturated solution, and 2S would represent the concentration of I⁺, because there are two moles of iodide ions for every mole of lead (II) ions that dissolve.

Thus, the mathematical expression to determine the value of S is:

Ksp = S(2S)²

It is important to understand that S represents the molar solubility of PbI₂, the concentration of Pb²⁺ ions in a saturated solution, and 2S reflects the stoichiometry of the iodide ions in the balanced dissolution equation.