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Quick question: Molar solubility

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betterfuture

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Someone explain this first. Then I will ask my question to see if I get it. Thank you.
 
Because the saturated cobalt (III) itself already has higher concentration of [OH-], mixing it with the saturated thallium(III), which has lower [OH-], is equivalent to diluting [OH-].

Actually, the mixing itself will also dilute [Co] and [Tl] so you cannot really say anything about TI unless volumes are given, but [Co] will absolutely not precipitate. And that strikes out B, D.

Edit: A and C are both possible.

I don't think whoever wrote that question understood the concept very well.
 
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I just don't understand how we are supposed to figure out the answer. We aren't really given much to figure out anything. My guess would have been D because they both have very small Ksp values.

Does this mean Cobalt hydroxide will dissolve more than thallium hydroxide? And why does cobalt not precipitate?