Question

Which best describes what happens when 50 mL of 0.0010M CaCl2 is added to 50 mL of 0.010M Na2SO4? (The Ksp of CaSO4 = 2.4 × 10–5.)


The solution will be at equilibrium.


CaSO4 will precipitate out of solution


No precipitation will occur.

Answer 1

When the solutions are diluted in half:
So [ Ca+2] = 0.001/2 = 0.0005 M
[SO4-2]= 0.01/2 =0.005

when Q = [Ca2+][SO4-2]
so by substitution:

Q = 0.0005*0.005 = 2.5x10^-6
by comparing with Ksp value
So when Q < Ksp
∴ the answer is no precipitation will occur, as the solution is unsaturated.