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Topic: Solubility calculations  (Read 779 times)

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Offline kdbmvp

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Solubility calculations
« on: February 23, 2019, 05:29:25 AM »
Hello,

I am a bit confused re. solubility calculations.

Calculate the solubility of Pb(OH)2 at pH 10. Setting up the expression for Ksp:

Ksp = [Pb2+][OH-]2 = 8* 10^-17 (Ksp value from SI chemical data)

pOH = 14 - 10 = 4, i.e. [OH-] = 10-4.

8*10-17 = [Pb2+][OH-]2. Solving for [Pb2+] we get that [Pb2+] = 8*10-9.

My question is: why couldn't we use the relationship between the concentrations of Pb2+ and OH- like we do with ICE tables, to get the result? I mean, couldn't we just divide the concentration of OH- by 2 and get the concentration of Pb2+..?

Offline chenbeier

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Re: Solubility calculations
« Reply #1 on: February 23, 2019, 06:19:14 AM »
This would be possible, if lead hydroxide would be dissolved like sodium hydroxide. But it doesn't. You need the soloubility product, because the soloubility is poor.
« Last Edit: February 23, 2019, 09:34:12 AM by chenbeier »

Offline kdbmvp

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Re: Solubility calculations
« Reply #2 on: February 23, 2019, 06:22:06 AM »
Thanks. Is it possible to deduce that from the Ksp value?

Offline chenbeier

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Re: Solubility calculations
« Reply #3 on: February 23, 2019, 09:39:13 AM »
How you want to do it?

Offline kdbmvp

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Re: Solubility calculations
« Reply #4 on: February 23, 2019, 11:19:06 AM »
I just wondered if you could from the Ksp value see that lead hydroxide has poor solubility, and that it wouldn't be possible to use the relationship between the concentrations.

Offline chenbeier

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Re: Solubility calculations
« Reply #5 on: February 23, 2019, 01:58:49 PM »
Of course you can.  Check the formula between soloubility, concentration and soloubility product

Offline kdbmvp

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Re: Solubility calculations
« Reply #6 on: February 24, 2019, 04:53:39 AM »
You mean the equation for Ksp?

Offline chenbeier

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