Question

A solution containing CaCl2 is mixed with a solution of Li2SO4 to form a solution that is 2.1 × 10-5 M in calcium ion and 4.75 × 10-5 M in sulfate ion. What will happen once these solutions are mixed? The Ksp for CaSO4 is 2.4 x 10-5.

Answer 1

Answer : The precipitate will not be formed when these solutions are mixed.

Explanation :

The chemical equation for the reaction of calcium chloride and lithium sulfate follows:

$CaCl_2(aq)+Li_2SO_4(aq)\rightarrow 2LiCl(aq)+CaSO_4(s)$

We are given:

Concentration of calcium ion = $2.1\times 10^{-5}M$

Concentration of sulfate ion = $4.75\times 10^{-5}M$

$K_{sp}=2.4\times 10^{-5}$

The salt produced is calcium sulfate.

The equation follows:

$CaSO_4(s)\rightleftharpoons Ca^{2+}(aq)+SO_4^{2-}(aq)$

The expression of $Q_{sp}$ (ionic product) for above equation follows:

$Q_{sp}=[Ca^{2+}]\times [SO_4^{2-}]$

Putting values of the concentrations in above expression, we get:

$Q_{sp}=(2.1\times 10^{-5})\times (4.75\times 10^{-5})\\\\Q_{sp}=9.9\times 10^{-10}$

There are 3 conditions:

• When $K_{sp}>Q_{sp}$; the reaction is product favored.  (No precipitation)
• When $K_{sp}$; the reaction is reactant favored.  (Precipitation)
• When $K_{sp}=Q_{sp}$; the reaction is in equilibrium. (Sparingly soluble)

As, the $K_{sp}>Q_{sp}$. The above reaction is product favored. This means that no salt or precipitate will be formed.

Hence, the precipitate will not be formed when these solutions are mixed.