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Topic: will a precipitate form?  (Read 10105 times)

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Offline Kaleyrvt

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Re: will a precipitate form?
« Reply #15 on: January 16, 2007, 05:36:16 PM »
1??? Man either I am just completely losing it or I am thinking way too hard!! It shouyldnt be this difficult!! BLAH! I am so sorry!

Offline Borek

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Re: will a precipitate form?
« Reply #16 on: January 16, 2007, 05:49:30 PM »
1 - you got it. Now, what the concentration of OH- in 0.233M NaOH is?
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Offline Kaleyrvt

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Re: will a precipitate form?
« Reply #17 on: January 16, 2007, 06:19:59 PM »
0.233 as well?

Offline Borek

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Re: will a precipitate form?
« Reply #18 on: January 16, 2007, 07:01:23 PM »
Exactly. Now, what about [Ca2+]?

And just to check if you really understand what is going on - what will be concentration of Cl-?
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Offline Kaleyrvt

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Re: will a precipitate form?
« Reply #19 on: January 16, 2007, 07:17:05 PM »
well the ration of CaCl2 is Ca:Cl2 = 1:2
Therefore Ca=0.066 and Cl= 2 x 0.066=0.132      ????
I hope this is right! ???

Offline Borek

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Re: will a precipitate form?
« Reply #20 on: January 16, 2007, 07:20:27 PM »
Therefore Ca=0.066 and Cl= 2 x 0.066=0.132

Good :)

Now plug concentrations into Ksp formula - if the result will be greater than the Ksp given for the particular compound, solid will precipitate.
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Offline Kaleyrvt

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Re: will a precipitate form?
« Reply #21 on: January 16, 2007, 07:28:22 PM »
so....
Ksp= [Ca2+][OH-]2
=[0.066][0.233]2
=3.58 x 10^-3

are these calcs right???
If theya re, then Ca(OH)2, is 7.9 x 10-6  which is < Ksp= [Ca2+][OH-]2, which is 3.58 x 10^-3 thus a precipitate will form????

cross my fingers?


Offline Borek

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Re: will a precipitate form?
« Reply #22 on: January 16, 2007, 08:14:10 PM »
Don't call result of your calculations Ksp - Ksp is constant that is characteristic for every substance. You do calculate a value of Ksp formula using  known concentrations - and then you compare it with known Ksp. In this case calculated value is 3.58*10-3 (you are OK), it is larger then Ksp for Ca(OH)2 - so the precipitate forms.

In short: you are right this time :)
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