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Author Topic: Sulfate / Sulfite Distinctions  (Read 413 times)

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Diamonds

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Sulfate / Sulfite Distinctions
« on: February 25, 2013, 08:17:04 PM »

Which of the following procedures will differentiate between solid sodium sulfite and solid sodium sulfate?

I. Make solutions of each and look for precipiates when added to 0.10M Ba(NO3)2
II. Add crystals of each to 0.10M HCl and look for bubbles
III. Make solutions of each and test with a pH indicator.

a) I
b) III
c) I, II
d) II, III

So I know III is correct, so it must be b or d. But then, I figured that it would be
SO42- + 2H+  :rarrow: H2O + SO3
and
SO32- + 2H+  :rarrow: H2O + SO2

Also, for choice I, I know it's not right (because I know the answer to the MC question), so that must mean that both BaSO4 [which I already know is insoluble] and BaSO3 are insoluble. Is it safe to assume as a general rule than an insoluble -ate will also make an insoluble -ite?
For example, can the same generalization be made about Cu(ClO4)2 and Cu(ClO3)2? I know that all chlorates are soluble, but does that all perchlorates are soluble? I don't think it is. So does this work on a case-by-case basis then?

Thanks in advance!
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Borek

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Re: Sulfate / Sulfite Distinctions
« Reply #1 on: February 25, 2013, 10:48:47 PM »

Ksp for barium sulfite is around 10-4.

You won't be able to decompose sulfate with hydrochloric acid, but I am not sure about sulfite.

I think making conclusions about -ite and -ate is unfounded.
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AWK

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Re: Sulfate / Sulfite Distinctions
« Reply #2 on: February 26, 2013, 03:00:15 AM »

II. HCl decompose salfates(IV)  but resulting SO2 is quite good soluble in water, hence only large amount of sulfite forms bubbles.

III. One from these solutions will be neutral, the other basic.
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ramboacid

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Re: Sulfate / Sulfite Distinctions
« Reply #3 on: February 26, 2013, 08:21:56 AM »

Quote
III. One from these solutions will be neutral, the other basic.

Wouldn't both solutions be basic? The sulfite solution would be more basic than the sulfate as it can take on two protons whereas the sulfate solution would be less basic as it can only take on one proton?
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Borek

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Re: Sulfate / Sulfite Distinctions
« Reply #4 on: February 26, 2013, 09:18:57 AM »

Wouldn't both solutions be basic? The sulfite solution would be more basic than the sulfate as it can take on two protons whereas the sulfate solution would be less basic as it can only take on one proton?

Generally speaking both sulfate and sulfite are diprotic, but you should compare pKas (or rather pKbs) to see which one will produce more basic solution. Sulfate solutions are for all practical purposes neutral.
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