[Sev3reD]

To what final concentration of NH3 must a solution be adjusted to just dissolve 0.15 mol of NiC2O4 (Ksp = 4 × 10-10) in 1.0 L of solution? The formation constant for the formation of Ni(NH3)6 2+ is Kf = 1.2 × 10^9

So I set up some equations:
Ni2+ + 6NH3 ---> Ni(NH3)6 2+
NiC2O4 -----> Ni2+ + C2O4 2-

NiC2O4 + 6NH3 -----> Ni(NH3)6 2+
.15           x                  0
-.15        -.15(6)           +.15
0              x-.9              .15

then using k = kf*ksp i set up the equation for k.. but i am not getting the right answer.  Can someone help?!

[Borek]

Once the salt has been dissolved - what is concentration of oxalate anion?

What is concentration of free Ni²⁺? (Hint: it is limited by solubility of oxalate)

What is concentration of the complex?

If you have concentration of the complex and free Ni²⁺, can you calculate concentration of ammonia?