Calculate the molar concentration of CaOH2 in a solution tha

Calculate the molar concentration of Ca(OH)₂ in a solution that has a pH of 10.05.

Solution

use:
pH = -log [H+]
10.05 = -log [H+]
[H+] = 8.913*10^-11 M

use:
[OH-] = Kw/[H+]
Kw is dissociation constant of water whose value is 1.0*10^-14 at 25 oC
[OH-] = (1.0*10^-14)/[H+]
[OH-] = (1.0*10^-14)/(8.913*10^-11)
[OH-] = 1.122*10^-4 M

Ca(OH)2   <—>   Ca2+   +   2OH-

[Ca(OH)2] = [OH-]/2
= (1.122*10^-4)/2
= 5.61*10^-5 M
Answer: 5.61*10^-5 M