Kb the same as KsP?

[kfcman289]

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When you have a salt such as ba(oh)2, does the ksp value equal the kb value since hydroxide ions are being donated to the solution?

 

[azor ahai]

What context is this being asked in? Yes, in this case since Ba(OH)2 is both a solid and a strong base which means you only consider the numerator when applying the law of mass action.

 

[erythrocyte666]

I would expect them to be different.
Ksp = [Ba2+][OH-]2 but Kb = [Ba2+][OH-]2/[Ba(OH)2], where Ba(OH)2 is the dissolved complex not the solid.
I would expect [Ba(OH)2] to be very small, and hence Kb would be very large but Ksp is still very small - explains why BaOH2 is a strong base but won't necessarily cause super high pH in solution due to its low solubility.
In other words, the high Kb tells us BaOH2 is a strong electrolyte (in comparison to NH3 which has much lower Kb) but with poor solubility