Precipitation Flashcards
Precipitation Method is also called ?
Argentometric Titration
Volumetric methods based on reactions that yield ionic COMPOUNDS OF LIMITED SOLUBILITY.
Precipitation Method
Analyte is titrated with a _____________________________ in the presence of a suitable indicator.
standard solution of a precipitating agent
Precipitation Method applies the _______________ principle.
solubility product
States that in a saturated solution of an ionic compound, the product of the molar activities (Ksp), has a constant value at any particular temperature and pressure.
Solubility Product Principle
Ksp meaning
Solubility Product Constant
Determined by
❖ Cessation of precipitation or appearance of turbidity
❖ Instrumental methods (potentiometry)
❖ Use of internal indicators
Endpoint
Potentiometry has?
Electrodes
Indicators
Colored lon - Volhard Method (Jacob Volhard)
Colored precipitate - Mohr Method (Karl Friedrich Mohr)
Colored Adsorption product - Fajan Method (Kazimiers Fajan)
Colored Ion
Volhard Method (Jacob Volhard)
Colored Precipitate
Mohr Method (Karl Friedrich Mohr)
Colored Adsorption Product
Fajan Method (Kazimiers Fajan)
Indicator used in Volhard’s Method
Ferric alum TS
(ferric ammonium sulfate, FeNH4(SO4)2)
Arrow up
Evolution of gas
Arrow down
Precipitation
In colored ion,
Slight excess thiocyanate ion reacts with ferric ion from the indicator producing a ________________ coloration.
faint reddish brown
Used in thiocyanate titrations.
Colored Ion
Indicator used in Colored Secondary Precipitate
Potassium chromate solution (Kr2CO4)
In colored secondary precipitate,
Chromate reacts with excess silver ions forming a secondary precipitate of _______ silver chromate.
reddish
Used in the titration of halides with standard silver nitrate solution.
Colored Secondary Precipitate
Indicator used in Fajan Method
• Dichlorofluorescein
• Eosin Y (Tetrabromofluorescein)
• TEE - fluorescence (Tetrabromophenolphthalein ethyl ester)
Eosin Y chemical name
Tetrabromofluorescein
TEE - fluorescence other name
Tetrabromophenolphthalein ethyl ester
Used as indicator in the titration of potassium chloride with standard silver nitrate solution.
Colored Adsorption Product
In colored adsorption product,
Silver chloride (ppt) formed is negatively charged due to adsorbed chloride ion and the indicator exists in the solution with a ______________.
greenish yellow
Direct titration with silver nitrate.
Colored Adsorption Product
In colored adsorption product,
slight excess of silver ion is adsorbed by the silver chloride precipitate colloid particles became positively charged which adsorb the fluoresceinate ions forming a __________ adsorption product.
reddish pink
The _______________ of a substance in the precipitation method is obtained by dividing the molecular weight by the total valence of the precipitating or precipitated ion
gram-equivalent weight
Method of titration if FAS is used as an indicator.
Volhard’s Method
What is the endpoint in Mohr’s Method?
Reddish silver chromate
Substances assayed:
❖ mainly used for determination of halides (Cl-, Br- & I-), SCN-,CN- and some compounds that form insoluble products (ppt) with AgNO3
Volhard Method is (direct/residual)?
Residual
Mohr’s Method is (direct/residual)?
Direct
