PRECIPITATION

Argentometric titration

Precipitation Method ❖ Also called

Precipitation Method

Volumetric methods based on reactions that yield ionic compounds of limited solubility

Precipitation Method

Analyte is titrated with a standard solution of a precipitating agent in the presence of a suitable indicator

Ionic product

WHAT exceeds the Ksp precipitation?

solubility product

Precipitation Method applies the WHAT principle

• Cessation of precipitation or appearance of turbidity

• Instrumental methods (potentiometry)

• Use of internal indicators

Endpoint

❖ Determined by

potentiometry

Endpoint ❖ Determined by

❖ WHAT Instrumental methods

internal

Endpoint ❖ Determined by

❖ Use of WHAT indicators

❖ Volhard’s Method

COLORED ION

Ferric alum / Ferric Ammonium Sulfate

Volhard’s Method

USE WHAT INDICATOR

Ammonium Thiocyanate

Volhard’s Method

USE WHAT VOLUMETRIC SOLUTION

Silver Nitrate

Volhard’s Method

USE WHAT PRIMARY STANDARD

Red color of Ferric Thiocyanate complex

Volhard’s Method

USE WHAT MANIFESTATION

Volhard’s Method

Slight excess thiocyanate ion reacts with ferric ion from the indicator producing a faint reddish brown coloration

❖ Mohr Method

COLORED SECONDARY PRECIPITATE

Potassium Chromate

Mohr Method

USE WHAT INDICATOR

Silver Nitrate

Mohr Method

USE WHAT VOLUMETRIC SOLUTION

Sodium chloride

Mohr Method

USE WHAT PRIMARY STANDARD

Red precipitate of Silver Chromate

Mohr Method

USE WHAT MANIFESTATION

Mohr Method

chromate reacts with excess silver ions forming a secondary precipitate of

reddish silver chromate

Mohr Method

Used in the Used in the titration of halides with standard silver nitrate solution

❖ Fajan Method

COLORED ADSORPTION PRODUCT

Silver Nitrate

Fajan Method

USE WHAT VOLUMETRIC SOLUTION

Adsorption indicator

• Dichlorofluorescein

• Eosin Y

• TEE - fluorescence

Fajan Method

USE WHAT INDICATOR

Sodium Chloride

Fajan Method

USE WHAT PRIMARY STANDARD

Change in the color of the silver halide precipitate

Fajan Method

USE WHAT MANIFESTATION

Fajan Method

slight excess of silver ion is adsorbed by the silver chloride precipitate

Fajan Method

colloid particles became positively charged which adsorb the fluoresceinate ions forming a reddish pink adsorptionproductc

Jacob Volhard

Colored Ion – Volhard Method

WHO

Karl Friedrich Mohr

Colored precipitate – Mohr Method

WHO

Kazimiers Fajan

Colored Adsorption product – Fajan Method

WHO

the total valence of the precipitating or precipitated ion

The gram-equivalent weight of a substance in the precipitation method is obtained by dividing the molecular weight by????

STANDARD SOLUTIONS

• Silver Nitrate,

• Potassium Thiocyanate

• Ammonium Thiocyanate

SUBSTANCE ASSAYED

• Silver compounds

• Mercuric compounds

• Halide compounds

• Theophylline compounds

• Silver Nitrate

• Sodium Chloride

• Dichlorofluorescein

ASSAY OF SODIUM LAURYL SULFATE FOR SODIUM CHLORIDE CONTENT

STANDARD SOL

PRIMARY

INDICATOR