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* 10^(-5)M`

Concentration of sulfate ion =
`4.75* 10^(-5)M`

`K_(sp)=2.4* 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+)]* [SO_4^(2-)]`

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

`Q_(sp)=(2.1* 10^(-5))* (4.75* 10^(-5))\\\\Q_(sp)=9.9* 10^(-10)`

There are 3 conditions:

• When
  `K_(sp)>Q_(sp)`; the reaction is product favored. (No precipitation)
• When
  `K_(sp)<Q_(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.