Posted by **Sally** on Wednesday, April 21, 2010 at 9:32pm.

Does precipitation occur when 100. mL of 0.050 M CaCl2 is added to 100. mL of 0.10 M K2SO4? Show calculations to support your response.

- AP Chemistry -
**DrBob222**, Wednesday, April 21, 2010 at 9:43pm
If a ppt occurs it will be what? CaSO4 perhaps.

(Ca+2)(SO4^-2) = Ksp.

Calculate (Ca^+2) and (SO$^-2) from the problem, substitute, and see if the ion product (usually called Qsp) is exceeded or not. If Qsp > Ksp, a ppt will occur. If not, no ppt will occur.

- AP Chemistry -
**Sally**, Wednesday, April 21, 2010 at 10:03pm
Thank you... Just to make sure... Since Qsp= 0.005 a precipitate will form.

- AP Chemistry -
**DrBob222**, Wednesday, April 21, 2010 at 10:21pm
I don't know about the conclusion since I don't know Ksp; however, I don't get 0.005 for Qsp.

- AP Chemistry -
**Sally**, Wednesday, April 21, 2010 at 10:46pm
The Ksp is 2.4 x 10^ -5. When I worked through this problem again, I came up with 2.0 x 10 ^-4 for Qsp

- AP Chemistry -
**DrBob222**, Wednesday, April 21, 2010 at 11:52pm
I don't know how you came up with that answer. Here is how you do it to determine if CaSO4 will ppt.

CaCl2 + K2SO4 ==> CaSO4 + 2KCl

Both CaCl2 and K2SO4 are diluted by a factor of two since the final volume is 200 mL and each is just 100 mL.

(CaCl2) = 0.05 x (100/200) = 0.025 M

(K2SO4) = 0.1 x (100/200) = 0.05

Qsp = (Ca^+2)(SO4^-2) = 0.025 x 0.05 = ??

Qsp exceeds Ksp; therefore, CaSO4 will ppt.

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