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Topic: Finding 'ph' value from 'Ksp'!!  (Read 11516 times)

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Offline shehri

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Finding 'ph' value from 'Ksp'!!
« on: April 21, 2009, 09:44:09 PM »
Dear friends,

              Plz. guide me how to calculate 'ph' of saturated solution of Zn(OH)2 whose Ksp is 2.1X10^-16?Thanks in advance.

Offline UG

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Re: Finding 'ph' value from 'Ksp'!!
« Reply #1 on: April 21, 2009, 10:15:54 PM »
Ks= [Zn2+][OH-]2

x mol Zn(OH)2   ::equil:: x mol Zn2+ + 2x mol OH-

So Ks(2.1X10-16)= x.(2x)2

x=3√(Ks/4)

Once you've got that you can calculate the solubility of OH- in mol L-1 and therefore the pH.

Offline Loyal

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Re: Finding 'ph' value from 'Ksp'!!
« Reply #2 on: April 22, 2009, 12:35:16 AM »
Ks= [Zn2+][OH-]2

x mol Zn(OH)2   ::equil:: x mol Zn2+ + 2x mol OH-

So Ks(2.1X10-16)= x.(2x)2

x=3√(Ks/4)

Once you've got that you can calculate the solubility of OH- in mol L-1 and therefore the pH.

Actually in that situation you need to do more.  The amount of OH being produced is rather small so you need to take the hydrolysis of water into account.
Chemistry Student(Senior) at WSU

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