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Offline jj2344

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Help with filtration problem
« on: November 28, 2014, 06:31:59 PM »
The problem is as follows:
100 ml of water may contain any of these ions, none of these ions, or all of these ions: Cu2+, Ba2+, Ag1+, Pb2+
Utilizing the solubility table, find out what is present in the water by adding in different compounds to see what precipitates out.

So far I've got the first step down and that is adding in NaC2H3O2 as it will form a precipitate ONLY with Ag and none of the others. The question essentially wants me to cause each ion to precipitate out one at a time while using Na, K, or NO3 to combine with the compound I'll be putting in (as they will stay soluble with whatever the unknown these ions are bonded with). Filtering out the precipitate if something I've already got set up so there's no need to worry about that, and you can do whatever you want to the water (as in split it into 3 beakers, heat it, etc). Any help at all would be appreciated thank you.

Offline Arkcon

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Re: Help with filtration problem
« Reply #1 on: November 28, 2014, 06:58:07 PM »
Well, sooner or later, people will ask you to format your formulas properly, we have sub- and superscript links just above the posting window for your convenience.

We can't be sure what NaC2H3O2 is, organic molecules cam in many different forms for the same numbers of atoms.  So you should describe that reagent more explicitly.  Assuming that's sodium acetate, I can only "bet" you're correct.  I don't expect silver to form a soluble acetate.  But it might, or it may not react at all, in that case, no precip.

If you could let us see your solubility table, it might help.  The standard solubility rules I know would use a slightly different procedure.
« Last Edit: November 29, 2014, 01:30:25 PM by Arkcon »
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Offline jj2344

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Re: Help with filtration problem
« Reply #2 on: November 29, 2014, 02:39:36 PM »
http://intro.chem.okstate.edu/HTML/SCSIMG/SCH1650.gif This is the table we were given except with regards to Chlorine and other Halides, Copper 1+ is also an exception.
« Last Edit: November 29, 2014, 04:43:18 PM by Arkcon »

Offline Arkcon

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Re: Help with filtration problem
« Reply #3 on: November 29, 2014, 04:44:47 PM »
OK, acetate doesn't appear to be listed in that table.  That table seems to be more like what I'm used to.  Now, can you use that table to begin to separate some of your components?
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Offline jj2344

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Re: Help with filtration problem
« Reply #4 on: November 30, 2014, 10:21:04 PM »
I've come up with something along the lines of this so far:

1) Split the 100ml beaker contents into 2 separate 50ml beakers.
2) In the first beaker, add NaC2H3O2 to precipitate silver.
3) Then Add in NaOH and see if it dissolves. If it does dissolve, we know there is Ba present. If it doesn't, we know Ba isn't present.
4) If it isn't present, we add in Na2SO4 to precipitate Pb (as Na2SO4 precipitates both Pb and Ba).
5) Finally, we add in NaCl to precipitate Cu if Ba isn't present.

Now in the second beaker, used only if Ba is present, I would still add in NaC2H3O2  to precipitate silver, but when I get to adding in Na2SO4 (knowing that Ba is present but not knowing if Pb is), I'm not sure how I can prove whether Pb is present or not. What could I possibly do?

Also in the table we were given, C2H3O2 1- is soluble with everything but Ag.

Edit* I noticed that in the table we were given, Cl- and other halides have  Ag1+ and Cu1+ listed as exceptions, but the question asked us to find out if Cu2+ is present or not. In this case, would adding in NaCl to a solution possibly containing Cu2+ cause a precipitate to form? Even if the charge is different?
« Last Edit: November 30, 2014, 10:38:59 PM by jj2344 »

Offline Borek

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Re: Help with filtration problem
« Reply #5 on: December 01, 2014, 03:36:34 AM »
Cu+ and Cu2+ are completely different cations with different properties.

What is a color of Cu2+? Color of the solution is its important property and often tells a lot about the identity of substances present.

You have split the sample into two parts, but you never used the second part.

Add in NaOH and see if it dissolves. If it does dissolve, we know there is Ba present. If it doesn't, we know Ba isn't present.

I don't see where you got it from.

Also, I am not convinced precipitating the acetate will work. I would start with chlorides, taking into account fact PbCl2 is soluble in hot water.
« Last Edit: December 01, 2014, 02:16:56 PM by billnotgatez »
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Offline jj2344

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Re: Help with filtration problem
« Reply #6 on: December 01, 2014, 07:38:48 AM »
With regards to the colour, I have absolutely no idea. Our teacher wants us to lay out a plan first before we are even shown the solution. Also regarding the NaOH, since OH is insoluble (with Ba listed as an exception), wouldn't adding NaOH as a solid as seeing whether it dissolves or not show whether Ba is present? Or is this incorrect?

Offline Borek

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Re: Help with filtration problem
« Reply #7 on: December 01, 2014, 08:46:20 AM »
With regards to the colour, I have absolutely no idea.

Google is your friend then.

Quote
Our teacher wants us to lay out a plan first before we are even shown the solution.

But once you see the solution you can use the color information, so you can laid out a plan that starts with "If the solution has color X then...".

Quote
Also regarding the NaOH, since OH is insoluble (with Ba listed as an exception), wouldn't adding NaOH as a solid as seeing whether it dissolves or not show whether Ba is present? Or is this incorrect?

OK, but why do you expect silver acetate to dissolve? You already have a precipitate in the test tube (I doubt you will do tests in a beaker), don't you?
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Offline jj2344

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Re: Help with filtration problem
« Reply #8 on: December 01, 2014, 12:05:50 PM »
What we will do is filter out the precipitates every time we see one form (yes we plan on doing the tests in a beaker), and I expect Ag to precipitate  if I add in NaC2H3O2 because on the table we were given, C2H3O2 is soluble with everything except Ag.

Offline Arkcon

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Re: Help with filtration problem
« Reply #9 on: December 01, 2014, 01:46:11 PM »
What we will do is filter out the precipitates every time we see one form (yes we plan on doing the tests in a beaker), and I expect Ag to precipitate  if I add in NaC2H3O2 because on the table we were given, C2H3O2 is soluble with everything except Ag.

That information is not in the image you provided.

This page here:  http://www.chem.sc.edu/faculty/morgan/resources/solubility/  Says that all acetates are soluble.

This page here: http://en.wikipedia.org/wiki/Silver_acetate Reports that silver acetate is soluble at a rate of 1g per 100 mL.  Consider, if you have a tiny amount of silver, even is a small amount of water. you may not get a precipitate.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

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