[noreen]

Cadmium(II) chloride is added to a solution of potassium hydroxide with pH of 9.62. (ksp Cd(OH)2=2.5x10-14)
At what concentration of Cd2+ does a precipitate first start to form?
The equation is Cd(Cl)2 + KOH -> Cd(OH)2, so the ksp expression would be Ksp=[Cd][OH]2. since the pH is 9.62, subtract it from 14 to get pOH which is 4.38. then take the inverse, 10^-4.38 to get 4.2x10-5 and then plug it into the ksp expression to get the concentration of Cd to be 2.5x10-5. is this correct, or am I missing a step?

[Borek]

Haven't check the math, but the general idea is correct.

[noreen]

thank you, i guess my math is incorrect then because the book says its concentration 1.4x10-5.

[Borek]

And my calculator says so

[taterpie14]

Keep in mind that when you use the Ksp for Cd(OH)2 the OH is squared because the reaction is: Cd(OH)2  Cd ²⁺+2OH^-.It should be set up like this: 2.5x10^-14=[Cd²⁺]x[4.17x10^-5]²
With that you should get 1.4x10^-5 as your answer.