Page 109 - Pharmaceutical_Analytical_Chemistry_1_Theoretical_Notes_Level_1

Mansoura National University
Pharm D-Clinical Pharmacy Program Level 1 Pharm. Anal. Chem. 1 (PC 101)

▪ Ksp is constant for each salt at each definite temperature and is a unitless

expression.

▪ If the ionic product is less than Ksp, no ppt is formed
▪ If the ionic product is more than Ksp, a ppt is formed

▪ The smaller the value of Ksp the lower the solubility is.

Solubility and Ksp (Three important definitions)

1) Solubility: quantity of a substance that dissolves to form a saturated solution

2) Molar solubility: the number of moles of the solute that dissolves to form a liter of
saturated solution

3) Ksp (solubility product): the equilibrium constant for the equilibrium between an ionic
solid and its saturated solution

Requirements for precipitation titrations

1) In order for a precipitate of an electrolyte to form, the ions of the electrolyte must be

present in a concentration more than the solubility product constant.
2) The precipitation reaction attains fast equilibrium after each addition of titrant.
3) Absence of interferences.

4) The indicator shows an obvious end point.

Quiz: Calculating Ksp from the Solubility

-5
Q: Solubility of AgCI is 1.1 x 10 M at 20 c, calculate K .
sp
1) Write the chemical equation for the substance dissolving and dissociating:
+
-
AgCl ↔ Ag + Cl

-
+
2) Write the Ksp expression: Ksp = [Ag ] [Cl ]
3) Insert the concentration of each ion and multiply:

-5
-10
-5
Ksp =[1.1 x 10 ] [1.1 x 10 ] = 1.2 x 10
104