How do I solve this? A generic salt, AB3, has a molar mass of 297 g/mol and a solubility of 7.30 g/L at 25 °C. What is the Ksp of this salt at 25 °C? AB3(s) <--> A^(3+) + 3B^(-)

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My teacher hasn't taught us anything about Ksp, so I'm not even sure where to start here. Am I supposed to convert to molarity first? I'm lost...

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Answer 1 · 2018-02-18T18:53:56

We address the solubility equilibrium....

#K_"sp"=27xx(0.0246)^4=9.89xx10^-6#..

We address the solubility equilibrium....

#AB_3(s) stackrel("solvent")rightleftharpoonsA^(3+) + 3B^(-)#..

..for which #K_"sp"=[A^(3+)][B^-]^3#

Now #S_"solubility"=[A^(3+)]#...clearly...

And so #K_"sp"=Sxx(3S)^3=27S^4#...where #S# is the GIVEN molar solubility...

And so we gots #S="moles of solute"/"volume of solution"#

#=((7.3*g)/(297.0*g*mol^-1))/(1*L)=0.0246*mol*L^-1#..

And so #K_"sp"=27xx(0.0246)^4=9.89xx10^-6#..

If you can't follow my tracks, raise an objection, and I will try to expand.