Precipitation titrimetry

• In titrimetric methods, precipitation titrimetry involves the reaction between the analyte and a standard reagent of known concentration, called titrant
• The stoichiometry of the reaction in titrimetry must be specific and reproducible
• All titration experiments have a chemical equivalence point called the end point
• The end point in titration is determined by the color change of an indicator or the characteristic change of a device signal
• Standard solution is a reagent with exactly known concentration used in titrimetry
• Titration is the process of adding a standard reagent to an analyte solution until the reaction is completed
• Back titration involves adding an excess of the standard reagent and determining this excess with a second standard titrant
• The equivalence point in titration is when the amount of standard reagent added is chemically equivalent to the analyte
• The end point in titration is when a physical change in the chemical equivalence point is observed
• Indicators are often added to the analyte solution in titration to produce an observable physical change at or near the equivalence point
• Primary standards are substances used as reference substances in volumetric and titrimetric methods with high purity
• Standard solutions used in titrimetry should be stable, react rapidly with the analyte, react completely, and undergo a selective reaction with the analyte
• Volumetric calculations in titrimetry are often performed using equations like mA = nA x MA and nA = V x cA
• To prepare standard solutions, the primary standard substance can be dissolved exactly or set with another standard solution
• In titration data analysis, molar concentrations can be calculated from standardization data
• The amount of analyte can be calculated from titration data obtained during the titration of the analyte in a sample
• The solubility of silver halides decreases as the concentration of silver ions increases due to the reaction between silver ions and halide ions to form a precipitate of silver halide

  
• The Ksp value is the equilibrium constant for the dissolution of a solid in a solvent
• In gravimetric titrimetry, the burette is replaced by a balance and a solution dispenser, and weight molarity (Cw) is used as the concentration unit
• Titration curves are graphs of a concentration-related variable against the volume of the reagent, showing the end point near the equivalence point
• Two types of titration curves are sigmoidal curves observed in a narrow region around the equivalence point and linear-segment curves where measurements are made on both sides of the equivalence point
• In precipitation titrimetry, compounds with limited solubility form precipitates, and titrimetric methods based on silver nitrate are called argentometric methods
• The titration curve for determining the concentration of halogen ions in aqueous solutions is the pAg graph against the added AgNO3 volume, with pre-equivalence, equivalence point, and post-equivalence calculations
• The completeness of the reaction affects the precision of the turning point in titration curves, with lower Ksp values leading to a larger change in pAg at the equivalence point
• Titration curves can be derived for anion mixtures with different solubilities, such as the titration of a solution containing iodide and chloride ions with AgNO3
• The titration of a 50.0 mL solution containing 0.05 M iodide and 0.08 M chloride with 0.10 M AgNO3 involves the precipitation of iodide before chloride ions precipitate

  
• At the equivalence point, all chloride ions have been precipitated, and the pAg is equal to 7.0
• The titration curve shows a rapid decrease in pAg, ending suddenly when chloride ions begin to precipitate
• Indicators for argentometric titrations can be determined chemically, potentiometrically, or amperometrically
• Chromate ion forms silver chromate with Ag+ in the equivalence point region, resulting in a brick-red color
• Adsorption indicators like fluorescein are used in precipitation titrations to indicate the endpoint
• The Volhard method involves titrating silver ions with a thiocyanate solution, where iron(III) acts as an indicator
• In the Volhard method, the solution turns red in the presence of excess thiocyanate ions and iron(III)
• A problem-solving example involves the quantitative precipitation of arsenic in the form of Ag3AsO4 using AgNO3 and KSCN titration
• Another problem-solving example deals with determining the percentage of warfarin in a sample using AgNO3 and KSCN titration