[achibaby1974]

ok. we have 6 unknowns. so, we call them A, B, C, D, E, F. We have to ID them from NaCl, MgO, CaCO3, NaNO3, CaCl2 and Na2CO3. We have the results but I still don't really understand what to do. 

A - is (aq) solub. and neutral
AgNO3- turned a milky white precipitate 

B - NOT (aq) solub. but is acid soluble
Na2CO3- white residue cloud/film on top only
NaOH2 - turned to white and a little fizzing, not much 

C - is (aq) solub. and neutral
NO change with any chems

D - is (aq) solub. and basic
HCl - started a little fizzing bubbles
AgNO3 - turned fizzing green with a brown precipitate

E - is (aq) solub. and neutral
NaOH- went from clear to white
AgNO3 milky white with precipitate
Na2CO3 - cloudy and white precipitate

F - is NOT (aq) solub and is NOT acid soluble either
NO CHEMS used

A salt is an ionic compound whose cation can't be H+ and anion can't be OH-. There must be a double displacement. How do I do these? I mean I know the solubility rules? Do I just have to break up each of the six salts until one of them works? I'm so lost. This wasn't covered in lecture but we have do it in lab, so now I'm frustrated. Does anyone understand these? 

[constant thinker]

Start with the most basic, solubility in water. Look up the solubility of all your possibilities and compare to your results. That'll help narrow things down because you'll have 2 compounds in one group and 4 in the other group.

From there you can further narrow down your water soluble compounds by pH.

Just looking at some of more defining characteristics of your possibilities and compare to the results. Example, for A you're looking for something that could have reacted with silver nitrate.

Post what you think some those may be, and someone is bound to comment on what you think and will steer you in the right direction.

[Arkcon]

Two or three of these outcomes are pretty easy.  But strung together like this, it will be hard for you to break down.  The fizzing, did it smell bad or odorless?  And what gases have those smells?  That's one bit of info you can work with.

[achibaby1974]

well I knew that A, C, D, E are water soluble.
B,F are not.

According to the Solubility rules:
Soluble
NaCl, NaNO3, CaCl2, Na2CO3

Insoluble
CaCO3, MgO??? (I don't know the rules on this)

I tested these salts with HCl, NaOH, Na2CO3, AgNO3 (all 1M solutions)
But one of the salts, Na2CO3 is the same as the Na2CO3 1M solution.
Does that mean the one with no rection in the water soluble C, is Na2CO3.   
Ok. now. I got a question. NaCl, NaNO3, CaCl2, Na2CO3, CaCO3 and MgO are all salts right? So, now I have to use the net ionic equation?
 
AgNO3 (aq) + NaCl(aq) ----> AgCl (s) + NaNo3

How do I know that? Why does it switch? Why is this considered double displacement? How can you tell what to do? What is this equation telling me?

Another question I have is that in lab we tested the salts to be be acid, base, or neutral. What for?
 

[Arkcon]

So, now I have to use the net ionic equation?
 
AgNO3 (aq) + NaCl(aq) ----> AgCl (s) + NaNo3

How do I know that? Why does it switch? Why is this considered double displacement? How can you tell what to do? What is this equation telling me?

There are two reasons why a double replacement reaction will happen.  One is solubility.  If an insoluble salt forms, then the replacement happens, like in your example.  On the other hand:

NaCl + HNO3 --> HCl + NaNO3, wont happen.  Or at least, won't look like anything in a small test tube.  Hint: Did you see something like that happen (er, not happen, as the case might be?)

The other reason a reaction will happen is due to reactivity.  The series should be in your book somewhere.  Failing that, you have to make a logical guess based on what you've seen in the world.  What is more likely to exist as a compound:  Gold?  Platinum?  No, we see those around all the time, shiny forever.  Silver?  Yeah, that's shiny, but we have to polish it, a bit. Lead?  Sometimes, often as a compound.  Iron? Yeah, that lasts a while, before it rusts.  Zinc?  That corrodes soon enough.  Ever seen free Sodium or Potassium in a lump?  No, that's too reactive.  The more reactive ones always replace the less reactive ones.

Another question I have is that in lab we tested the salts to be be acid, base, or neutral. What for?

Salts of a strong acid and a weak base are weakly acidic.  Conversely for the saly of a weak acid and a strong base.  You'll have to know the definition of weak, and strong,  acid and base, however.

[Borek]

So, now I have to use the net ionic equation?
 
AgNO3 (aq) + NaCl(aq) ----> AgCl (s) + NaNo3

To add to what Arkcon said: if you will write net ionic equation you will see what is happening and why.

[constant thinker]

Insoluble
CaCO3, MgO??? (I don't know the rules on this)

I guess technically MgO isn't water soluble, it's water reactive. It reacts with water to form Mg(OH)₂. If your having trouble finding properties on MgO look up CaO since it has similar properties.

[Borek]

IIRC MgO reaction with water is rather slow, besides, Mg(OH)₂ is weakly soluble, so what you get is usually a suspension, not solution. I don't remember how fast it reacts with acids - for sure it is much less reactive than CaO.