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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: AhmedEzatAlzawalaty on March 03, 2007, 03:34:34 PM

Title: precipitimetry
Post by: AhmedEzatAlzawalaty on March 03, 2007, 03:34:34 PM

why AgCN dissolves AgCl AgBr AgI but not .

Title: Re: precipitimetry
Post by: Borek on March 03, 2007, 03:46:41 PM

Try to reword your post, it doesn't make any sense now.

Title: Re: precipitimetry
Post by: english on March 04, 2007, 03:49:09 PM

I think he may be asking why AgCN dissolves, but the silver halides do not?

Title: Re: precipitimetry
Post by: Borek on March 04, 2007, 07:12:51 PM

Could be.

Title: Re: precipitimetry
Post by: AWK on March 05, 2007, 08:42:17 AM

Quote from: ahmedezat on March 03, 2007, 03:34:34 PM

why AgCN dissolves AgCl AgBr AgI but not .

Do you mean KCN?

Title: Re: precipitimetry
Post by: english on March 06, 2007, 03:11:50 AM

Quote from: AWK on March 05, 2007, 08:42:17 AM

Quote from: ahmedezat on March 03, 2007, 03:34:34 PM

why AgCN dissolves AgCl AgBr AgI but not .

Do you mean KCN?

Silver cyanide is insoluble?  I don't recall that from anywhere.  Thanks for the refresher.

Title: Re: precipitimetry
Post by: Borek on March 06, 2007, 04:44:34 AM

pKso = 15.66

CN^- is sometimes called pseudohalide - and for a reason :) Just like SCN^-, OCN^- and others I am not sure about (N₃^-?).

However, AgCN is a fancy compound ;) While it is only weakly soluble, Ag(CN)₂^- complex has high stability constant (log K = 20.48). In effect reaction

2AgCN(s) <-> Ag(CN)₂^- + CN^-

increases AgCN solubility.

That's what I suspect from the very beginning, I am just not sure.

Title: Re: precipitimetry
Post by: AhmedEzatAlzawalaty on March 09, 2007, 08:23:24 AM

 i meant to say that why AgCN dissolves AgI,AgBr,AgI but not Ag2S and why silver ammine on the other hand dissolves AgCl efficiently , AgBr slightly and AgI not dissolved at all by it?

Title: Re: precipitimetry
Post by: Borek on March 09, 2007, 09:03:20 AM

Quote from: ahmedezat on March 09, 2007, 08:23:24 AM

i meant to say that why AgCN dissolves AgI,AgBr,AgI but not Ag2S and why silver ammine on the other hand dissolves AgCl efficiently , AgBr slightly and AgI not dissolved at all by it?

You are repeating exactly the same statement for the second or third time. This statement is not clear in English. Try to ask the same question using different words, or try to describe th eexperiment that you refer to.

Title: Re: precipitimetry
Post by: AhmedEzatAlzawalaty on March 14, 2007, 04:33:58 PM

i mean AgI AgBr AgCl are dissolved efficiently in AgCN but when i tried to dissolve Ag2S in AgCN it didnt dissolve at all.
And Silver ammine dissolves all the AgCl , some of AgBr and none of AgI solids.
here AgCN and Silver ammine are solvents.
i think its clear now.

Title: Re: precipitimetry
Post by: AWK on March 15, 2007, 03:01:54 PM

Quote from: ahmedezat on March 14, 2007, 04:33:58 PM

i mean AgI AgBr AgCl are dissolved efficiently in AgCN but when i tried to dissolve Ag2S in AgCN it didnt dissolve at all.
And Silver ammine dissolves all the AgCl , some of AgBr and none of AgI solids.
here AgCN and Silver ammine are solvents.
i think its clear now.

Not in AgCN but in KCN or NaCN

Title: Re: precipitimetry
Post by: AhmedEzatAlzawalaty on March 15, 2007, 04:48:13 PM

Ok that s right KCN or NaCN but why ? can u explain me what happened.

Title: Re: precipitimetry
Post by: AWK on March 19, 2007, 05:57:20 AM

Because anion CN- forms a strong soluble complex with Ag+

Title: Re: precipitimetry
Post by: AhmedEzatAlzawalaty on March 19, 2007, 01:04:22 PM

SO?

Title: Re: precipitimetry
Post by: AWK on March 20, 2007, 06:00:24 AM

AgCl(s) + 2CN^-(aq) = [Ag(CN)₂^-](aq) + Cl^-(aq)

Title: Re: precipitimetry
Post by: AhmedEzatAlzawalaty on March 20, 2007, 08:10:15 AM

what about Ag2S , why isnt it dissolved in KCN?

Title: Re: precipitimetry
Post by: AWK on March 20, 2007, 10:59:01 AM

You can calculate solubility of Ag2S in KCN using solubility product of Ag2S and formation constant of Ag(CN)2-

Title: Re: precipitimetry
Post by: AhmedEzatAlzawalaty on March 20, 2007, 03:46:50 PM

i know this,i mean why isnt Ag2S soluble in KCN regarding solubility product?