[BrightOrange]

I have two questions that are not directly related but I did not want to separate into different posts.

I understand if you don't want to read/help with both, but any comments at all are appreciated.

(1)  I have a solution of ions and I need to separate them into separate containers.  The specific problem was asking about Pb2+, Ba2+, and K+.

Using a solubility table I was able to see that I could start by adding Cl- to precipitate PbCl2.  After filtering I could then add H2SO4 to precipitate Ba2+ as BaSO4.  After another round of filtering that would leave K+ in solution by itself, and all three have been separated.

First of all, that would work right?  It seems to be the best answer.  However what if those chemicals weren't available?  Could I get Pb2+ out using H2S for PbS2 instead of HCl?  What if there were other ions in solution as well?

My problem isn't that I can't work the question given, but that I just used a table to look it up instead of really understanding why some are soluble and others are not -- or how I could use my head to figure it out.  I don't want to have to run to a table (or have a bunch of tables memorized) in order to know what would or wouldn't work.  For instance K+ and Cl- make KCl but it's not going to precipitate.  And so on.

Tips?

(2)  I had more trouble with this one.  I have four acids -- HCl  H2SO4  H3PO4  HNO3 -- and they are in old bottles that the labels have fallen off of.  So I need to figure out which is which.  Preferably more than one way.  To be a strong acid you need to fully dissociate yes?  So HCl and HNO3 are strong for sure.  I thought H2SO4 was, and H3PO4 wasn't, but now I'm not sure.

The first idea I had was to titrate them.  For instance could I add BaCl2 to all of them and only see a precipitate for the H2SO4?  That would ID that one.  However AgNO3 would react with ... two of them?  HCl and HNO3?  Not sure what to use about the other ones.

Would they all have different pH values?  I could just look that up on a table if so and use a pH meter?

Would I need to do some kind of titration curve ... and, actually, they would all have different pKa values, and I could find that out from a titration curve?  What would I titrate with though?  How would I calculate that for the polyprotic ones?

I think there are also some ion tests that I could do like I wanted to try for the cations, but I'm not sure which ones would precipitate only for one of the acids and not the others -- nor do I know how to find out.  Anyone know a good table for anions like these?  Or what the standard tests are?

Also dunno if some will dissolve things others will not.   I guess I could add NaOH to all of them and eat anything that precipitates out -- the one with table salt will have been HCl (haha, yeah, bad joke I know).

Tips?  Help?

I'm trying pretty hard to think these through fully but a little nudge or two would be greatly appreciated.

[AWK]

First of all, that would work right?  It seems to be the best answer.  However what if those chemicals weren't available?  Could I get Pb2+ out using H2S for PbS2 instead of HCl?  What if there were other ions in solution as well?

This will work much better. PbS (not PbS₂) has a very low solubility in water. Solubility of PbCl₂ is about 10 g/L at room temperature.
_{What if there were other ions in solution as well?
My problem isn't that I can't work the question given, but that I just used a table to look it up instead of really understanding why some are soluble and others are not -- or how I could use my head to figure it out.  I don't want to have to run to a table (or have a bunch of tables memorized) in order to know what would or wouldn't work.}
Good textbook on qualitative analysis is invaluable. Tbles in this case are insufficient.
_{2)  I had more trouble with this one.  I have four acids -- HCl  H2SO4  H3PO4  HNO3 -- and they are in old bottles that the labels have fallen off of.  So I need to figure out which is which.  Preferably more than one way.  To be a strong acid you need to fully dissociate yes?  So HCl and HNO3 are strong for sure.  I thought H2SO4 was, and H3PO4 wasn't, but now I'm not sure.}
Read analysis of anions in your textbook. AgNO3 and BaCl2 tests are sufficient in this case.

[Borek]

My problem isn't that I can't work the question given, but that I just used a table to look it up instead of really understanding why some are soluble and others are not -- or how I could use my head to figure it out. I don't want to have to run to a table (or have a bunch of tables memorized) in order to know what would or wouldn't work.

No simple way of predicting solubility. Memorizing few simple rules is the best approach.

I had more trouble with this one.  I have four acids -- HCl  H2SO4  H3PO4  HNO3

Again, application of solubility rules. You need to select cations that will react as selectively as possible with anions present.