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Topic: Solubility of a solid when added to a base?  (Read 2878 times)

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Offline skibum143

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Solubility of a solid when added to a base?
« on: November 04, 2010, 08:09:43 PM »
What is the solubility of MX3 solid in 0.10 M M(NO3)3?
MX3  M3+ + 3X1- (Ksp = 1.9e-09)

At first I thought that:
M(NO3)3 -> M3+ + 3NO3-
                 x        (0.10 + 3x)
So 1.9E-9 = (x)(0.1)^3, but that was wrong...

Then I thought:
MX3 -> M3+ + 3x-
      (0.1 + x)    3x
So 1.9E-9 = (0.1)*(3x)^3, but that was wrong too...   
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Offline Borek

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Re: Solubility of a solid when added to a base?
« Reply #1 on: November 05, 2010, 03:54:58 AM »
Quote from: skibum143 on November 04, 2010, 08:09:43 PM
MX3 -> M3+ + 3x-
      (0.1 + x)    3x

OK

Quote
So 1.9E-9 = (0.1)*(3x)^3

Not OK.
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Offline rabolisk

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Re: Solubility of a solid when added to a base?
« Reply #2 on: November 06, 2010, 01:50:21 PM »
The second approximation should work, especially given only 2 sig figs. What was the answer given?
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Offline Borek

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Re: Solubility of a solid when added to a base?
« Reply #3 on: November 06, 2010, 05:49:56 PM »
Approximation may work, but you have to know you are approximating. I guess x was just accidentally lost.
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