Qvault Equilibrium shift question

[Toadesque]

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Can someone explain this one to me? I may be remembering this concept wrong, but I thought when a precipitate forms there is a shift to the left in the equilibrium (Ksp < Qsp as more solid formed). The explanation says the opposite. I feel like I might be interpreting the question incorrectly...

 

[starnova]

a + b <<>> c + d
if you remove c, the equilibrium will shift to the right to compensate for it
think of the removal of c as something like the formation of insoluble starch from sugar

 

[Toadesque]

Ok thanks

so was the way I thinking of it completely wrong? I'm pretty certain that what I said was true, but I guess it has no application to what this problem was asking?

 

[starnova]

your do have a valid point, and it's true that when Q > K, it shifts left
but for this question, I think it means a (aq) + b (aq) <> c (aq) + d (aq)
and you add whatever to remove c completely or turn it into solid, this way you have less product and it will shift to the right by "forming insoluble product" due to le chatelier's principle

what you're thinking is if you have 1 M K2CO3 and 1 M AgNO3, will a precipitate form if Ag2CO3 has ksp of 2 for example, that's when you compare its ksp to your qsp that you calculate
if your qsp is 3, precipitate will form and will shift left in order to reach the equilibrium