[medianji]

I need help with this problem...
Compute pH of the saturated solution of La(OH)₃ in the 2x 10^-4 M aqueous solution of La(NO3)₃. Ksp of La(OH)3 is 1.00x10^-19 M^4

I know that La(NO₃)₃ = La³+ + 3NO₃

then I make an ICE table, but I am not sure wich one gets the -x or the +x.

Is this right? or is it the other way

    La(OH)₃ == La⁺³    +   3OH^-
I   0               2x10^-4          0
C  -x              +x                 +3x
E  -x              2x10^-4+x      +3x

THANKS!

[Borek]

La(OH)₃ is solid, so you don't have to deal with its concentration. Other than that it looks OK.

[ooosh]

It's will be easy if you know how to use the equation of Ksp,for La(OH)3

 Ksp[La(OH)3]=[La3+]*([OH-]^3)

 pH=14-pOH

pOH=-log [OH-]

when you have the three equations above you only need to find the concentration of La3+ in the solution.