TITRIMETRIC METHODS OF ANALYSIS BASICS OF ANALYTICAL CHEMISTRY PROF.DR.ENDANG ASIJATI M.Sc. Titrimetric Methods • Includes a group of analytical methods that are based upon determining the quantity of a reagent of unknown strength that is required to react completely with the analyte. Titrimetric Methods • Volumetric titrimetry – A type of titrimetry in which the standard reagent is measured volumetrically. • Gravimetric titrimetri – A type of titrimetry in which the mass of the standard reagent is measured. • Coulometric titrimetry – A type in which the quantity of charge in coulombs required to complete a reaction with the analyte is maesured. Titration? • A process in which a standard reagent is added to a solution of an analyte until the reaction between the analyte and the reagent is judge to be complete. • Back-titration – A process in which the excess of a standard solution used to react with an analyte is determined by titration with a second standard solution. Equivalence and end Points • Equivalence point – Related to the amount (mol/mek) • End point – Related to the physical sign that associate with the condition of chemical equivalence. The end point is express in range, the range should address to the equivalence point. Standard? • Standard Solution – A primary standard – A secondary standard • Standardization – A process in which concentration of a volumetric solution is determined by using it to titrate a known mass of a primary standard. PRIMARY STANDARD • HIGH PURITY • ATMOSPHERIC STABILITY • INDEPENDENT OF HUMIDITY • MODEST COST • LARGE MOLAR MASS ALGEBRAIC RELATIONSHIP • AT THE EQUIVALENCE POINT – Equivalent A = Equivalent B – Mol A = Mol B (if the reaction is 1:1) TITRATION CURVES FOR WEAK ACIDS • At the beginning, the solution contains only a weak acid or a weak base, and the pH is calculated from the concentration of that and its dissociation constant. • After various increment of titrant have been added, the solution consists of a series of buffers. The pH of each buffer can be calculated from the analytical concentration of the conjugate base or acid and the residual concentration of the weak acid or base. TITRATION CURVES FOR WEAK ACIDS • At equivalence point, the solution contains only the conjugate of the weak acid or base being titrated, and the pH is calculated from the concentration of this product • Beyond the equivalence point, the excess of strong acid or base titrate represses the acidic or basic character of the reaction product to such an extent that the pH is governed largely by the concentration of the excess titrant.