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Topic: Ksp problem - The final confusion  (Read 533 times)

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Offline sharbeldam

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Ksp problem - The final confusion
« on: December 21, 2019, 01:08:16 AM »
We mix 10 grams of BaCl2 (does not has a ksp) with 5 grams of Ag2SO4 (has a ksp), we get a precipitate.
1) What does that precipitate contain?
2) What ions does the solution contain?

Given Ksp of BaSO4=1.08*10^-10 } Ksp of AgCl=1.5*10^-10  } ksp of Ag2SO4=2.8*10^-5

My confusion:
since BaCl2 dissociate completely -> BaCl2(s) -> Ba+2(aq) + 2Cl-(aq)
Finding the moles of Ba+2=0.048moles
Finding the moles of Cl-=0.096moles

Ag2SO4 is more soluble than BaSO4 and AgCl, but it has been said by lab professor than we can say that it dissolves completely and then test ourselves (Why?, what if it doesn't?)

So if we suppose it dissolves completely, i can treat it like BaCl2.
Finding the moles of Ag+=0.032moles
Finding the moles of SO4-2=0.016moles

Precipitate:
BaSO4 -> 0.016 moles 3.73 grams
AgCl-> 0.032 moles 4.58 grams

Ions remaining:
SO4-2=5.6*10-9     Ba+2=0.032       Cl-=0.064         Ag+=2.34*10^-9

How can we test now that our theory that Ag2SO4 dissolve completely? all of our calculations are based on that it did, what if it dissolved 50% or 80%, then we will have less Ag+ and SO4-2 and all our calculations will be wrong, is there a way to verify it? and when we can we use that theory that a salt dissolves completely since a ksp was given (it's not that small but still).

Appreciate the help
Thanks
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Offline AWK

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Re: Ksp problem - The final confusion
« Reply #1 on: December 21, 2019, 02:49:37 AM »
The solubility of silver sulfate is about 8 g/L at RT. Solubilities of AgCl and BaSO4 are of order miligram/L.
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Offline sharbeldam

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Re: Ksp problem - The final confusion
« Reply #2 on: December 21, 2019, 02:57:05 AM »
The solubility of silver sulfate is about 8 g/L at RT. Solubilities of AgCl and BaSO4 are of order miligram/L.
I get that but as a college problem, how would a student know, since only a ksp is given, usually that means that it shouldn't dissolve completely like bacl2.
As a college student, how would you test to verify that it did in fact dissolve completely?
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Offline AWK

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Re: Ksp problem - The final confusion
« Reply #3 on: December 21, 2019, 03:10:28 AM »
You can calculate solubilities from Ksp
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Offline sharbeldam

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Re: Ksp problem - The final confusion
« Reply #4 on: December 21, 2019, 03:15:56 AM »
Okay it gives me s(SO4-2)=0.019M and 2s(Ag+)=0.038M [Concentrations that can be dissolved]

and i have 0.032M Ag+2 in the solution and 0.016M SO4-2 in the solution, that means because they are less than "s" they can all be dissolved in the soluton, right?

Now it makes sense :) they do not say that in lab, Thanks AWK and please correect me if im wrong
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Offline AWK

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