Volumetric Analysis In many acid-base reactions, the equilibrium is displaced almost completely toward the product side. These reactions may be considered quantitative and can be used as the basis for the analysis of the amount of acid or base in a given sample. The process is termed volumetric analysis. The requirements are: 1) Only a single, specific reaction must take place between the unknown substance and the known substance used for the analysis. 2) The unknown substance must react completely and rapidly with the added standard reagent. ie; it must be a quantitative reaction. 3) An indicator or method must be available to signal when all the unknown substance has reacted with the added standard reagent. The usual objective is to determine the mass or percentage of a qualitatively identified component in a sample whose quantitative amount is unknown. If the sample is a solution, the objective may be to determine its molar concentration. Acid-Base Titration An acid-base titration is just a method by which we can perform a volumetric analysis. The concentration of an acid-base solution may be determined by measuring the volume of the base of known concentration needed to react completely with a specific volume of an acid solution. Definitions Standard solution: A solution of known concentration. Titration: the process of adding the standard solution from a graduated tube in controlled amounts. Buret: a graduated tube with a dispensor control at the bottom. Stoichiometric Point: the point at which equal molar quantities of reactants are present. Chemical Indicators: a chemical that will change colour at or very near the ph of the stoichiometric point. Endpoint: The place in the titration when the indicator changes colour. The indicator used, should in theory coincide with the stoichiometric point of the reaction. A 0.660 mol/L NaOH solution is used to determine the molar concentration of H2SO4 solution. What is the molarity of the acid, 20.0 mL of which is just neutralized by 36.0 mL of the standard base? This is a standard problem which can be solved using: MaVa = MbVb where M is the molarity, V is the volume, a is 'of the acid', b is 'of the base'. Therefore Ma = Mb * Vb = 0.660 mol/L * 36.0 mL = 1.19 mol/L                                 Va                                 20.0 mL Follow-Up Problems 1. What is the molarity of a hydrochloric acid solution, 30.0 mL of which is just neutralized by 48.0 mL of 0.100 mol/L NaOH? 2. How many mL of 0.100 mol/L HCl are required to neutralize 25.0 mL of 0.100 mol/L Ba(OH)2?