Posted by Sally on .
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,
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,
Thank you... Just to make sure... Since Qsp= 0.005 a precipitate will form.

AP Chemistry 
DrBob222,
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,
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,
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.