What Causes Precipitation When Silver Nitrate Reacts with Different Ions?

[HorseBox]

We were doing anion identification tests in the lab today and I noticed silver nitrate had a tendency to react with the samples and something would precipitate out. I also noticed silver nitrate is the reactant used for chloride tests. Is what precipitates out in that case silver chloride? Also is it only silver halides that precipitate out like this or will silver nitrate react with other ions and form products which precipitate out?

 

[pzona]

Find a solubility chart, that should help you. In this case, yes it was probably silver chloride, but silver halides aren't the only silver compounds that will precipitate out. Some other important ones include oxides, sulfides, phosphates, and carbonates.

 

[HorseBox]

Thanks. I found this solubility chart
http://intro.chem.okstate.edu/1515SP01/Database/Solub.html
and noticed is states that chloride ions will always be soluble in water unless in conjunction with silver, mercury or lead ions. Is this true or are there exceptions to that rule? Also let's say I had an unknown solution the only thing I knew is it contained 1 ionic compound. Let's say I added a silver salt and a white precipitate formed. Could I assume there are chloride ions present and the white precipitate is silver chloride or are do some of the other anions you listed produce the same white precipitate when combined with a silver cation?

You mentioned oxides. I observed that adding AgNO3 to NaOH formed some kind of precipitate. I'm assuming it was AgOH that precipitated. Do hydroxides fall into the category of oxides too?

 

[Bohrok]

Look at hydroxides in the link you gave and you'll see that they're insoluble with some exceptions.

 

[pzona]

Thanks. I found this solubility chart
http://intro.chem.okstate.edu/1515SP01/Database/Solub.html
and noticed is states that chloride ions will always be soluble in water unless in conjunction with silver, mercury or lead ions. Is this true or are there exceptions to that rule?

This rule for chlorides is true for anything you'll be using, based on my assumption that you're somewhere around the high school level of chemistry. There are probably (I can't say for sure) some other metals which will make insoluble chlorides, but Ag, Hg, and Pb are the most important and common ones.

Also let's say I had an unknown solution the only thing I knew is it contained 1 ionic compound. Let's say I added a silver salt and a white precipitate formed. Could I assume there are chloride ions present and the white precipitate is silver chloride or are do some of the other anions you listed produce the same white precipitate when combined with a silver cation?

No, you can't assume this is silver chloride. Silver iodide and silver bromide are also insoluble silver compounds, so you'll need to do some further testing. In this kind of situation the solubility chart is a really good tool to use.

You mentioned oxides. I observed that adding AgNO3 to NaOH formed some kind of precipitate. I'm assuming it was AgOH that precipitated. Do hydroxides fall into the category of oxides too?

You're probably right that it is AgOH, as most hydroxides are insoluble (the solubility chart should tell you this). But no, hydroxides do not fall into the category of oxides.

 

[HorseBox]

Thanks for the replies. I'm in the first year of uni. Didn't go to high school so I'm pretty much self taught but there are certain areas I skipped. Identifying ions was one of them.

 

[pzona]

Oh, alright, you're the same year as me then. Ion identification is pretty important, but you've got a skill which often has to be learned: asking the right questions. Good luck in your studies.