What is the Ksp for mercury (I) carbonate (Hg2CO3) if a saturated solution of Hg2CO3 has a concentration of Hg2+ equal to 4.2×10−6 M?

Question

What is the Ksp for mercury (I) carbonate (Hg2CO3) if a saturated solution of Hg2CO3 has a concentration of Hg2+equal to 4.2×10−6 M?

Hg2CO3(s)↽−−⇀2Hg+(aq)+CO2−3(aq)

Answer 1

Hg2CO3

Hg2Co3 → 2Hg+ + CO3-

Ksp = [Hg+]^2[CO32-] = [4.2 x 10^-6]^2[2.1 x 10^-6] = 39.7 x 10

^-18

= 3.97 x 10^-17 = Ksp

Answer 2

Your question is a little misleading and/or incorrect because you have written Hg²⁺ = 4.2x10^-6 M and you also have 2Hg⁺ as a product of the solubility reaction. These are inconsistent with each other. Further, you have written CO₂^3- which is not correct, as it should be CO₃^2-. Ignoring these issues, and assuming that the dissolution process is Hg₂CO₃(s) <==> 2Hg⁺(aq) + CO₃^2-(aq) we can write the Ksp expression as:

Ksp = [Hg⁺]²[CO₃^2-]

Since [Hg+] = 4.2x10^-6 M, the [CO₃^2-] will = 1/2 * 4.2x10^-6 M = 2.1x10^-6 M

Ksp = [4.2x10^-6]²[2.1x10^-6] = 3.7x10^-17