Ksp=2.4x10^-5 for calcium sulfate. What is the molar solubility of calcium sulfate in pure water? What is the mass solubility of calcium sulfate in pure water, expressed in g/L?

Ksp=2.4x10^-5 for calcium sulfate.

What is the molar solubility of calcium sulfate in pure water?

What is the mass solubility of calcium sulfate in pure water,
expressed in g/L?

1 Answer
Sep 7, 2016

Answer:

(a)

#sf(4.9xx10^(-3)color(white)(x)"mol/l")#

(b)

#sf(0.67color(white)(x)"g/l")#

Explanation:

(a)

Calcium sulfate is sparingly soluble. In a saturated solution the aqueous ions are in equilibrium with the insoluble salt:

#sf(CaSO_(4(s))rightleftharpoonsCa_((aq))^(2+)+SO_(4(aq))^(2-))#

For which

#sf(K_(sp)=[Ca_((aq))^(2+)][SO_(4(aq))^(2-)]=2.4xx10^(-5)color(white)(x)"mol"^2."l"^-2)#

The solubilty #sf(s)# of the salt is equal to #sf([Ca_((aq))^(2+)])#.

Since #sf([Ca_((aq))^(2+)]=[SO_(4(aq))^(2-)])# we can write:

#sf(K_(sp)=s^(2)=2.4xx10^(-5))#

#:.##sf(s=sqrt(2.4xx10^(-5))=4.9xx10^(-3)color(white)(x)"mol/l")#

This is the molar solubility.

(b)

To find the mass solubility we multiply by the mass of 1 mole. I will assume we are using the anhydrous salt #sf(CaSO_4)# for which the #sf(M_r=136.1)#

#:.# Mass solubility = #sf(4.9xx10^(-3)xx136.1=0.67color(white)(x)"g/l")#