What is the scandium ion concentration for a saturated solution of Sc(OH)₃ if the K_sp for Sc(OH)₃ is A)3.00 × 10^-8 M B)1.31 × 10^-8 M C)3.22 × 10^-10M D)3.76 × 10^-8 M

Question

Quizplus · Accepted Answer

First, write out the balanced equation for the dissociation of Sc(OH)3:
Sc(OH)3 <=> Sc3+ + 3OH-
The Ksp expression for this reaction is:
Ksp = [Sc3+][OH-]^3
We are given that Ksp = 1.1 x 10^-18. 
At saturation, the concentration of Sc3+ and OH- are equal, so we can assume that [Sc3+] = [OH-]. Let x be the concentration of Sc3+ in mol/L. Then:
Ksp = x(x)^3 = x^4
1.1 x 10^-18 = x^4
x = 1.31 x 10^-5 M = [Sc3+]
Answer: B

What Is the Scandium Ion Concentration for a Saturated Solution