finding [OH]

[joonkimdds]

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Find the concentration of OH in X(OH)2 if Ksp of this is 4 x 10 ^-18?

find pH from above.

find concentration of each ions in a saturated solution of PbBr2. Ksp = 2.1 x 10^-6

Thank you~ it would be great if you could show me every step 😉

 

[pbure9]

So for the first one...

Ksp = [X][OH]^2 = 👎(2n)^2 = 4n^3 = 4x10^-18
divide both sides by 4 and you have n^3 = 1x10^-18
now take the cube root of 1x10^-18 and you get 1x10^-6 which is equal to X.
OH- however, is double that (2n), so its concentration is 2x10^-6.
This means pOH is approximately 5.8 or so and pH is 14-5.8 = 7.2.

That looks right to me 🙂

As for the second one its pretty much the same thing its just that the numbers don't seem too friendly when you work it out.

 

[alanan84]

So for the first one...

Ksp = [X][OH]^2 = 👎(2n)^2 = 4n^3 = 4x10^-18

Why do you make the OH 2n?

 

[pbure9]

So for the first one...

Ksp = [X][OH]^2 = 👎(2n)^2 = 4n^3 = 4x10^-18

Why do you make the OH 2n?

well since the reaction would be as follows:

X(OH)2 --> X2+ + 2OH-, therefore the concentration of OH- will be twice that of X