LABORATORY WORK PRECIPITATION TITRATION. MOHRS METHODS Objective: Determination of chloride in solid and liquid samples by the Mohr Method Learning Outcome:  Students understand the terms volumetric analysis, morarity, molality normality and redox titration.  Students acquire the skill to prepare standard solutions of silver nitrate and sodium chloride.  Students understand the apparatus used for a titration.  Students acquire the skill to perform the precicpitation-titration in the real lab after understanding the different steps. Titration is a process by which the concentration of an unknown substance in solution is determined by adding measured amounts of a standard solution that reacts with the unknown. Then the concentration of the unknown can be calculated using the stoichiometry of the reaction and the number of moles of standard solution needed to reach the so called end point. Precipitation titrations are based upon reactions that yield ionic compounds of limited solubility. Classification of methods precipitation titration (on titrant): 1. Argentometry 2. Thiocyanatometry 3. Mercurometry 4. Sulphatometry 5. Hexacianoferratometry Characteristics of Precipitation Titration:  They are fast and the stoichiometry is known and reproducible, (no secondary reactions of interference).  They are complete or can be quantified depending on the amount of solubility product (in general a precipitation titration is considered complete when K sp < 10 -8 )  An indicator can be used to find the equivalence point or titration end point which, for this type of titration, corresponds to when precipitation of the analyte under analysis is complete. The Solubility Product Constant When an ionic compound is dissolved in water, it usually goes into solution as the ions. When an express of the ionic compound is mixed with water, equilibrium occurs between the solid compound and the ions in the saturated solution: 1