Two (related) chemistry 105 questions.

[blackhole123]

1. (bunch of filler info about barium sulfate). Given the following starting compounds, write for each compound a balanced total ionic equation and a balanced net ionic equation to prepare BaSO4: Ba(OH)2, BaCl2, BaCO3. If the the rxn occurs in more than one step then write the rxn as a series of sequential reactions. Identify the type of each reaction.

 

For this one do I just add some sort of soluble sulfate compound that reacts with the starter compound to produce an insoluble precipitate? I'm guessing the first one is some sort of acid. Would you add H2SO4 and get (for the molecular equations, I know how to do ionic equations thats not the problem):

 

Ba(OH)2(aq)+ H2SO4(aq) --> BaSO4(s) + 2H2O(l)

 

the next one,

 

BaCl2(aq)+ Na2SO4(aq) --> BaSO4(s) + 2NaCl

 

and

 

BaCO3(aq)+ K2SO4(aq) --> BaSO4(s)+ K2CO3

 

Is this right?

 

I think I solved this one too, look at edit #2.

 

2. Describe how you would separate the cations or anions in the following aqueous solutions by forming a precipitate. Include your logic with your description.

 

a) NaNO3 and Ba(NO3)2 (separate Na^+ from Ba^2+)

 

It goes from a-e but I just need to know how to do and I can do the rest. I'm confused when it talks about separating Na from Ba. They are only together in the sense that soluble compounds in a solution are ions floating around. So do you add a compound that would form an insoluble precipitate or something like in the first problem?

 

EDIT: I think I've figured out what to do in #2. You need to add something that will precipitate Na+ out but not Ba2+, then filter and do the same for Ba2+.

 

EDIT 2: Looked some more and I got that barium sulfates are insoluble (I just did a whole problem on it, DUH!) So if I add a random sulfate like K2SO4 it will make BaSO4 ppt but Na will still be in there? Does making a new compound that is a ppt count as separating them? Does NaNO3 change at all?

Edited September 28, 2009 by blackhole123

[varnis]

When you have an insoluble ppt, you have separated one ion from the other, in the sense that the Na+ is left in solution. So filtering the ppt will give a solid and a solution. As for the last part of edit #2: No, you can leave the remaining ions either dissociated (Na+(aq) + NO3-(aq)) or as sodium nitrate (NaNO3(aq))

[blackhole123]

Alright thanks.

 

One more easy question. I have recorded in my lab notes that when I added CuSO4 to water (anhydrous, white powder), it turned blue. But I think when you add CuSO4(s) to water it just makes CuSO4(aq). I know the pentahydrate form is blue. Why did my solid turn blue? Is the pentahydrate forming?

 

Also, when I add CuSO4 5H20(aq) to solid zinc what does it form, ZnSO4 or ZnSO4 5H20?

Edited September 29, 2009 by blackhole123

[Fuzzwood]

The water disappears in the solution. Its not like a seperate ion or something. It it water which is complexed to the copper, causing the blue color.

[Theophrastus]

And following up on fuzzwoods point, as its simply a matter of complexation, you can expect that the hydration of your resulting compound, will have little to do with your initial reactants (ie, just because the CUSO4 is pentahydrate, doesn't mean ZnSO4 shall have the same same degree of hydration, particularly given an aqueous solution). If I'm not mistaken ZnSO4 would likely take on the heptahydrate form, were it to be extracted from the solution.