Question

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^(-)

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...

Answer 1

We address the solubility equilibrium....

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

Explanation:

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.