9th Class Chemistry: Precipitation Titration

Precipitation Titration

• A solution is a homogeneous mixture of two or more substances, whereas a suspension is a heterogeneous mixture, and a precipitate is an insoluble solid that forms in a solution.

Solubility Product Constant (Ksp)

• The solubility product constant (Ksp) is the product of the concentration of the ions that are present in a saturated solution of an ionic compound.
• Ksp represents the level at which a solute dissolves in a solution; the more soluble a substance is, the higher the Ksp value it has.
• For a salt AaBb, Ksp = [A+]a.[B-]b.

Examples of Ksp Calculations

• For AgCl, Ksp = [Ag+].[Cl-].
• For Pb3(PO4)2, Ksp = [Pb2+]3.[PO43-]2.

Calculating Ksp Values

• Copper(I) bromide has a measured molar solubility of 2.20x10-4 mol/L at 25°C, so Ksp = 4.0x10-8 mol2/L2.
• Bismuth sulfide (Bi2S3) has a solubility of 1.0x10-15 mol/L at 25°C, so Ksp = 1.1 x 10-73.

Precipitation Reaction

• A solution is 1.5 x 10–6 M in Ni2+, and Na2CO3 is added to make the solution 6.0 x 10–4 M in CO32–. Since Q < Ksp, no precipitate will be formed.

Titration

Standardization of Potassium Permanganate

• Transfer 10 ml oxalic acid solution (0.1 M) into a conical flask and add 20 ml, 2N H2SO4.
• Heat the solution to 60-70°C and titrate slowly with potassium permanganate to the faint pink colour end-point.

Redox Titration

• Standardization of potassium permanganate is used for the determination of iron.
• Transfer 10 ml iron solution into a conical flask and add 20 ml, 2N H2SO4.
• Titrate slowly with potassium permanganate to the faint pink colour end-point.