- #1
Zynwyx
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Hi :)
I've been having some trouble getting my head around Tollens' solution, but especially the mechanisms in its preparation. There is next to no information on the internet regarding its mechanisms and my chemistry knowledge isn't advanced enough to be able to really make any idea of what's going on. Hopefully someone here with a knowledge of chemistry can help me out?
So, in the first step of its preparation a few drops of a strong alkali (e.g. sodium hydroxide) is added to some aqueous silver nitrate, and a brown precipitate of silver oxide forms. This is the first place I am unsure about what happens; precisely, how the silver oxide is formed. All that I know conclusively is that the Ag+ ions in the silver nitrate solution are hydrated as [Ag(H2O)2]+ ions, then that the OH- ions from the alkali protonate the aqua ligands to form [Ag(OH)2]- ions. But from here how is Ag2O formed? My textbook says the hydroxy ligands are further protonated (wouldn't that give improbable [Ag(O)2]3- anyway?) but since the silver oxide formed is a binary oxide i.e. two Ag to each O, I first assumed that there would need to be an interaction between two individual Ag complexes in order to provide the two Ag needed for each O.
But silver oxide is a polymer according to Wikipedia so would there be a kind of "build up" of silver oxide crystals/polymers on nucleation sites using the Ag in solution kind of like Lego blocks?
The next problem is the addition of ammonium hydroxide to the mixture. This "dissolves" the silver oxide and diamminesilver(I) ions are formed in solution [Ag(NH3)2]+. By dissolve I assume it means the silver oxide is split into aqueous ions, ie [Ag(H2O)2]+ again and some other species (I'm thought OH-)? Or is there some sort of ligand substitution reaction going on between Ag2O and NH3 (even though Ag2O isn't a complex I thought... but in an analogous way)
Any clarification would be really helpful on this, I know my thinking is deeply flawed on all of this. Tbh I am getting more confused the more I think about this and its causing many sleepless nights :P. Hopefully being able to see the mechanism for this will help me think clearer about how the actual Tollens' test mechanism works as well!
I've been having some trouble getting my head around Tollens' solution, but especially the mechanisms in its preparation. There is next to no information on the internet regarding its mechanisms and my chemistry knowledge isn't advanced enough to be able to really make any idea of what's going on. Hopefully someone here with a knowledge of chemistry can help me out?
So, in the first step of its preparation a few drops of a strong alkali (e.g. sodium hydroxide) is added to some aqueous silver nitrate, and a brown precipitate of silver oxide forms. This is the first place I am unsure about what happens; precisely, how the silver oxide is formed. All that I know conclusively is that the Ag+ ions in the silver nitrate solution are hydrated as [Ag(H2O)2]+ ions, then that the OH- ions from the alkali protonate the aqua ligands to form [Ag(OH)2]- ions. But from here how is Ag2O formed? My textbook says the hydroxy ligands are further protonated (wouldn't that give improbable [Ag(O)2]3- anyway?) but since the silver oxide formed is a binary oxide i.e. two Ag to each O, I first assumed that there would need to be an interaction between two individual Ag complexes in order to provide the two Ag needed for each O.
But silver oxide is a polymer according to Wikipedia so would there be a kind of "build up" of silver oxide crystals/polymers on nucleation sites using the Ag in solution kind of like Lego blocks?
The next problem is the addition of ammonium hydroxide to the mixture. This "dissolves" the silver oxide and diamminesilver(I) ions are formed in solution [Ag(NH3)2]+. By dissolve I assume it means the silver oxide is split into aqueous ions, ie [Ag(H2O)2]+ again and some other species (I'm thought OH-)? Or is there some sort of ligand substitution reaction going on between Ag2O and NH3 (even though Ag2O isn't a complex I thought... but in an analogous way)
Any clarification would be really helpful on this, I know my thinking is deeply flawed on all of this. Tbh I am getting more confused the more I think about this and its causing many sleepless nights :P. Hopefully being able to see the mechanism for this will help me think clearer about how the actual Tollens' test mechanism works as well!