Question

Ksp [caso4] = 2.4 × 10-5. determine the molar solubility of caso4 in a solution containing 0.100 m na2so4.

Answer 1

Using Common ion effect and Le-Chatlier's Principle,
Let, conc. of Ca2+ present in solution = a,
SO4(2-) ions are present in solution because of CaSO4 and Na2SO4,
Let conc. of SO4^(2-) ions present in solution because of CaSO4 = b
and conc. of SO4^(2-) ions present in solution because of Na2SO4 = c = 0.1 m (given)

Dissociation of CaSO4 can be represented as follows,
CaSO4 ↔ Ca^2+     +      SO4^(2-) 
∴ a = b

Given that Ksp of CaSO4 = 2.4 X 10^(-5)
In present system, Ksp = a(b+c) = a(a+ 0.1) = 2.4 X 10^-5
Now, CaSO4 is a sparingly soluble salt, ∴ a <<< 0.1, ∴ a + 0.1 ≈ 0.1

∴ Ksp = 0.1a = 2.4 X 10^(-5)
∴ a = 2.4 X 10^(-4) m

Thus, effective conc. of CaSO4 in solution is 2.4 X 10^(-4) m