text: Your question is not very clear to me.\nWhat are alphaNi and alphaY ?\nAlpha can be used for lots of different things like activity, dissociation degree, coefficient for chaning molarity to normality, etc but here I fail to see what it represents, especially alphaY (what is Y?).\n\nIf the complexation equilibrium constant is truly 10^18.6 then the reaction is practically quantitative and at 100% and 200% [Ni+2] will practically approximate zero and the pNi will be huge. If you want us to help you find exact values please clarify your question and send me an email to edit my answer accordingly.