Applications of Neutralization Titrations

A Teutralization titrations are widely used to determine the concentration ofana-J V lytes that are themselves acids or bases or are convertible to such species by suitable treatment J Water is the usual solvent for neutralization titrations because it is readily available, inexpensive, and nontoxic. Its low temperature coefficient of expansion is an added virtue. Some analytes, however, are not titratable in aqueous media because their solubilities are too low or because their strengths as acids or bases are not sufficiently great to provide satisfactory end points. Such substances can often be titrated in a solvent other than water. We shall restrict our discussions to aqueous systems. 

In Chapter 14, we noted that strong acids and strong bases cause the most pronounced change in pH at the equivalence point. For this reason, standard solutions for neutralization titrations are always prepared from these reagents. 

Hydrochloric acid is widely used for titration of bases. Dilute solutions of the reagent are stable indefinitely and do not cause troublesome precipitation reactions with most cations. It is reported that 0.1 M solutions of HCl can be boiled for as long as an hour without loss of acid, provided that the water lost by evaporation is periodically replaced 0.5 M solutions can be boiled for at least 10 minutes without significant loss. 

Solutions of perchloric and sulfuric acid are also stable and are useful for titrations where chloride ion interferes by forming precipitates. Standard solutions of nitric acid are seldom encountered because of their oxidizing properties. 

Standard solutions are prepared by diluting weighed quantities of this acid to accurately known volumes. 

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PART III Classical Methods of Analysis 311 Chapter 12 Gravimetric Methods of Analysis 314 Chapter 13 Titrimetric Methods Precipitation Titrimetry 337 Chapter 14 Principles of Neutralization Titrations 368 Chapter 15 Titration Curves for Complex Acid/Base Systems 395 Chapter 16 Applications of Neutralization Titrations 428 Chapter 17 Complexation Reactions and Titrations 449... 

Spreadsheet Summary In Chapter 8 of Applications of Microsoft Excel in Analytical Cheniistiy, we extend the treatment of neutralization titration curves to polyfunctional acids. Both a stoichiometric approach and a master equation approach are used for the titration of maleic acid with sodium hydroxide. 

The last definition has widespread use in the volumetric analysis of solutions. If a fixed amount of reagent is present in a solution, it can be diluted to any desired normality by application of the general dilution formula V,N, = V N. Here, subscripts 1 and 2 refer to the initial solution and the final (diluted) solution, respectively V denotes the solution volume (in milliliters) and N the solution normality. The product VjN, expresses the amount of the reagent in gram-milliequivalents present in a volume V, ml of a solution of normality N,. Numerically, it represents the volume of a one normal (IN) solution chemically equivalent to the original solution of volume V, and of normality N,. The same equation V N, = V N is also applicable in a different context, in problems involving acid-base neutralization, oxidation-reduction, precipitation, or other types of titration reactions. The justification for this formula relies on the fact that substances always react in titrations, in chemically equivalent amounts. 

One important application of acid-base titrations is the determination of the alkalinity of various kinds of samples. It is an especially important measurement for the proper treatment of municipal water and wastewater. Alkalinity of a water sample is defined as its acid-neutralizing capacity. It is determined by titrating the water sample with standard acid until a particular pH is achieved. The alkalinity value... 

To study nonexchangeable acidity, active and exchangeable acidity has to be blocked (Hargrove and Thomas 1982 Thomas and Hargrove 1984). In potentio-metric titration, the main source of exchangeable acidity is the permanent charge of aluminosilicates, which can be neutralized by a support electrolyte in high concentration (e.g., 0.1 mol/dm3 sodium salt) (Chapter 2, Section 2.4.3). The application of the support electrolyte makes it possible to use the constant capacitance model, too. 

Electrometric Titration Precipitation Reactions.—One of the most important practical applications of electrode potentials is to the determination of the end-points of various typos of titration the subject will be treated here from the standpoint of precipitation reactions, while neutralization and oxidation-reduction processes are described more conveniently in later chapters. 

An important variation in the application of nonaqueous solvents has been to add various neutral (see below) solvents to the sample solvent, the reagent, or both, or to use mixtures of solvents. Fritz dissolved weakly basic samples in a variety of solvents such as chloroform, nitrobenzene, ethyl acetate, and acetonitrile and then titrated with perchloric acid in acetic acid using a glass electrode or methyl violet as indicator. Dioxane has been substituted for acetic acid as a solvent for titrant perchloric acid, and sharper titration curves often are observed. Such a reagent is no longer strictly anhydrous when no provision is made to remove water from the 72% perchloric acid used to prepare the reagent. 

Neutralization of the separator effluent is usually accomplished with sodium hydroxide however, lime or ammonia are occasionally used. A two-stage system using well-mixed tankage of suitable size is recommended. The neutralization invariably occurs on the steep part of the titration curve in these applications. Any inappropriate design, such as an excessively remote pH controllers, will result in a nonfunctional system. As a result, it is highly recommended that an individual experienced in designing pH control systems reviews the final design. 

The most important application of the Volhard method is the indirect determination of halide ions. A measured excess of standard silver nitrate solution is added to the sample, and the excess silver is determined by back-titration with a standard thiocyanate solution. The strong acidic environment required for the Volhard procedure represents a distinct advantage over other titrimetric methods of halide analysis because such ions as carbonate, oxalate, and arsenate (which form slightly soluble silver salts in neutral media but not in acidic media) do not interfere. 

Neutralization titrations are used to determine the innumerable inorganic, organic, and biological species that possess inherent acidic or basic properties. Equally important, however, are the many applications that involve conversion of an analyte to an acid or base by suitable chemical treatment followed by titration with a standard strong base or acid. 

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