Why is My Free Energy Calculation from Ksp Incorrect?

[elitespart]

Okay so I'm confused. In my book it says that ksp for Ca(OH)2 = 6.5E-6 and $$\Delta G=-898.5$$ yet when I use the equation $$\Delta G=-RTln(Ksp)$$ the value I get is 29.59KJ/mol. I used R=8.314 and T=298K. What's up with that? Thanks.

 

[lluviata]

Hint: Consider the implications of the solubility constant versus the
\Delta G\
of formation (which is the value you have given), specifically the reactions involved.