May 26, 2019, 09:47:53 AM
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### Topic: Solubility calculations  (Read 826 times)

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#### 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+..?

#### 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 »

#### 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?

#### chenbeier

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

#### 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.

#### 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

#### kdbmvp

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

#### chenbeier

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##### Re: Solubility calculations
« Reply #7 on: February 24, 2019, 07:12:25 AM »