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Author Topic: How does increasing the acidity change the solubility?  (Read 4160 times)

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xangelofxdeathx

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How does increasing the acidity change the solubility?
« on: March 27, 2007, 09:20:45 PM »

This is a question that I was wondering about:

Lead(II) Flouride, Lead (II) chloride, Lead(II) Bromide, and Lead(II) Iodide are all slightly soluble in water. Which lead salt will increase in solubility when its saturated solution is acidified?

A) PbF2
B) PbCl2
C) PbBr2
D) PbI2

I don't recall learning anything about how solubility would change when a solution is made more acid in my AP Chem class yet. Could someone briefly summarize what happens and how you get to the answer? (The answer is A by the way)
« Last Edit: March 27, 2007, 09:33:34 PM by xangelofxdeathx »
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Borek

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Re: How does increasing the acidity change the solubility?
« Reply #1 on: March 27, 2007, 09:29:44 PM »

What happens when you acidify solution of a weak acid?
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xangelofxdeathx

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Re: How does increasing the acidity change the solubility?
« Reply #2 on: March 27, 2007, 09:31:42 PM »

The acid gets stronger, so the forward reaction becomes favored more, so the solubility increases?

Is that correct?



EDIT: For this problem, does it actually have to do with the solubility rules? I just realized that all of them are insoluble salts except for A. Is that why the answer is A? Because increasing the acidity of an insoluble salt in general would still leave the salt insoluble?
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Yggdrasil

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Re: How does increasing the acidity change the solubility?
« Reply #3 on: March 27, 2007, 09:52:39 PM »

With F- in an acidic solution you have the following equilibrium:

F- + H+ <--> HF

Since this decreases the amount of F- in solution, then for

PbF2 <--> Pb2+ + 2F-

will favor the forward reaction (because Le Chatelier's principle states that when you remove a product, the reaction will favor the production of more product).

In contrast, HCl, HBr, and HI all fully dissociate in solution, so none of the chloride, bromide, or iodide gets tied up by the acid.
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AWK

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Re: How does increasing the acidity change the solubility?
« Reply #4 on: March 28, 2007, 05:35:11 AM »

Quote
In contrast, HCl, HBr, and HI all fully dissociate in solution, so none of the chloride, bromide, or iodide gets tied up by the acid.
Yggradrasil is right as far as we do not take into account the ionic strength of solution (and an acid added  do not contain a common ion with salt, and do not forms more insoluble salts, eg PbClF is far less soluble then PbCl2 of PbF2 themselves).
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