ion exchange column

[DeFused]

I'm hoping someone can help clarify how an ion exchange column works. I thought I understood it but I think I might have some concepts misinterpreted. I attached an image of a problem that I got confused on.

From what I got, AgS precipitates into the tube <--- this is column where Ag and Zn basically swap. When I read the explanation for the answer (B) it made sense to be because since Ag2S precipitates into the tube ZnS has to be more soluble.

What I was confused about is what I read from TBR, "The column is filled with an ion
exchange resin. The cation to be precipitated must have a lower molar solubility with the anion of the resin than the salt in the resin."

Isn't this saying that Zn's solubility with S has to be less than Ag2S in order for Zn to precipitate out? Or is this actually referring to the cation that is precipitated in the column?

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[Incontrol]

I think your confusion comes from "Isn't this saying that Zn's solubility with S has to be less than Ag2S in order for Zn to precipitate out"

Zn does not precipitate out, it becomes an ion (Zn+2) and leaves. The precipitate kinda mean that you will form a solid salt in a solution (not the exact definition).

So TBR explanation "The column is filled with an ion
exchange resin. The cation to be precipitated [Ag+] must have a lower molar solubility with the anion of the resin[S-2] than the salt in the resin [ZnS]."
in other words. Ag2S should be less soluble than ZnS, which is why it can displace(not precipitate) the Zn+2 out.

 

[BerkReviewTeach]

Great systematic explanation Incontrol.

Note to the OP: As a courtesy to people who haven't taken that exam, you should list the source of the question in the title of the thread, so that people who plan to take that exam can avoid the thread and not spoil the answer to a future question. Thank you.

 

[DeFused]

Thanks that really helped. I was thinking the same thing when I was looking at the question.

Also changed the title!

 

[dudewheresmymd]

for #55 p.209 (related to ion exchange) why does [H3O+] = 2[Sr2+] ? A bit confused.. from answer explanation on page 228.