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A popular lecture demonstration involves the sequential precipitation and dissolution...

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lak-86 | Student, Undergraduate | (Level 1) Salutatorian

Posted July 8, 2013 at 4:41 PM via web

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A popular lecture demonstration involves the sequential precipitation and dissolution of several slightly soluble silver compounds beginning with a

[Ag+] = 0.0050 M. Use the information below to answer the following questions about this demonstration.
Ksp values;

Ag2SO4 = 1.4×10^(-5)

What must the [SO4^(2-)] be in order to start precipitation in a solution in which [Ag+] = 0.005 M?

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jeew-m | College Teacher | (Level 1) Educator Emeritus

Posted July 8, 2013 at 4:53 PM (Answer #1)

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`Ag_2SO_4 rarr 2Ag^++SO_4^(2-)`

By the `K_(sp)` notation we can write;

`K_(sp) = [Ag^+]^2[SO_4^(2-)]`

`1.4xx10^(-5) = (0.005)^2[SO_4^(2-)]`

`[SO_4^(2-)] = (1.4xx10^(-5))/(25xx10^(-6))`

`[SO_4^(2-)] = 0.56M`

So we need 0.56M of sulphate ion concentration in order to precipitate `Ag_2SO_4`

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