Procedures in volumetric analysis

Volumetric analysis, also known as titrimetric analysis, is a quantitative technique used to determine the amount of a particular substance in a solution of unknown composition. 

The volume of standard solution that reacts with the substance in the test solution is accurately measured. This volume, together with a knowledge of concentration of the standard solution and the stoichiometric relationship between the reactants, is used to calculate the amount of substance present in the test solution. Specific examples of the different types of calculations involved are shown in Chapters 22 to 25. 

Acid-base or neutralization reactions, where free bases are reacted with a standard acid (or vice versa). These reactions involve the combination of hydrogen and hydroxide ions to form water. 

Complex formation reactions, in which the reactants are combined to form a soluble ion or compound. The most important reagent for formation of such complexes is ethylenediamine tetra-acetic acid, EDTA (as the disodium salt). 

Precipitation reactions, involving the combination of reactants to form a precipitate. 

A stoichiometric titration is one with a known reaction path, for which a chemical reaction can be written, and having no alternative or side reactions. 

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Many titration procedures in volumetric analysis use an indicator that changes color to signal the endpoint of the titration. For example, acid-base titrations are often performed... 

Here are some examples to illustrate stoichiometry calculations in volumetric analysis. The key step is to relate moles of titrant to moles of analyte. We also introduce the Kjeldahl titration as a representative volumetric procedure. 

The volume of reagent (titrant) required for stoichiometric reaction of analyte is measured in volumetric analysis. The stoichiometric point of the reaction is called the equivalence point. What we measure by an abrupt change in a physical property (such as the color of an indicator or the potential of an electrode) is the end point. The difference between the end point and the equivalence point is a titration error. This error can be reduced by subtracting results of a blank titration, in which the same procedure is carried out in the absence of analyte, or by standardizing the titrant. using the same reaction and a similar volume as that used for analyte. 

The scientist who was responsible for the introduction of titrimetry into mainstream chemistry was Gay-Lussac. He further developed the apparatus used in volumetric analysis and was the first to use the word burette (Figure 14.3). In 1832 he introduced precipitation titrations for the estimation of silver. Sodium chloride solution was added to a solution of a silver salt until no further precipitation occurred. This was a time-consuming procedure as near the endpoint the precipitate had to be allowed to settle before each new portion of sodium chloride was added. 

Part—I has three chapters that exclusively deal with General Aspects of pharmaceutical analysis. Chapter 1 focuses on the pharmaceutical chemicals and their respective purity and management. Critical information with regard to description of the finished product, sampling procedures, bioavailability, identification tests, physical constants and miscellaneous characteristics, such as ash values, loss on drying, clarity and color of solution, specific tests, limit tests of metallic and non-metallic impurities, limits of moisture content, volatile and non-volatile matter and lastly residue on ignition have also been dealt with. Each section provides adequate procedural details supported by ample typical examples from the Official Compendia. Chapter 2 embraces the theory and technique of quantitative analysis with specific emphasis on volumetric analysis, volumetric apparatus, their specifications, standardization and utility. It also includes biomedical analytical chemistry, colorimetric assays, theory and assay of biochemicals, such as urea, bilirubin, cholesterol and enzymatic assays, such as alkaline phosphatase, lactate dehydrogenase, salient features of radioimmunoassay and automated methods of chemical analysis. Chapter 3 provides special emphasis on errors in pharmaceutical analysis and their statistical validation. The first aspect is related to errors in pharmaceutical analysis and embodies classification of errors, accuracy, precision and makes... 

Volumetric analysis involves using a solution of accurately known concentration, a standard solution, in a quantitative reaction to determine the concentration of the other reactant. The procedure is known as titration. One solution is measured quantitatively into a conical flask using a pipette. The other solution is dispensed from a burette until a permanent colour change appears in the solution in the conical flask. 

Procedures in which we measure the volume of reagent needed to react with analyte are called volumetric analysis. In this chapter, we discuss principles that apply to all volumetric procedures and then focus on precipitation titrations. We also introduce spectrophotometric titrations, which are especially useful in biochemistry. 

Sample Solution (Caution Perform this procedure in a fume hood, and wear safety glasses.) Transfer 1 g of sample, accurately weighed, into a large test tube. Add 1 mL of nitric acid. Place the test tube in a rack in a boiling water bath. As soon as the rusty tint is gone, add 1 mL of 30% hydrogen peroxide dropwise to avoid a vigorous reaction, and wait for bubbles to form. Stir with an acid-washed plastic spatula if necessary. Remove the test tube from the water bath, and let it cool. Transfer the solution into a 10-mL volumetric flask, and dilute to volume with Butanol-Nitric Acid Solution, and mix. Use this solution for analysis. 

Acid-base titrations are an example of volumetric analysis, a technique in which one solution is used to analyze another. The solution used to carry out the analysis is called the titrant and is delivered from a device called a buret, which measures the volume accurately. The point in the titration at which enough titrant has been added to react exactly with the substance being determined is called the equivalence point, or the stoichiometric point. This point is often marked by the change in color of a chemical called an indicator. The titration procedure is illustrated in Fig. 4.18. 

To summarize, then, the eurrent-time measurements required for a coulometric titration are inherently as accurate as or more accurate than the comparable volume-molarity measurements of a classical volumetric analysis, particularly where small quantities of reagent are involved. Often, however, the accuracy of a titration is not limited by these measuremenis hut by the sensitivity of the end point in this respect, the two procedures are equivalent. 

In volumetric cruilysis, the concentration of a Mlution is found by measuring the volume of solution that will react with a known volume of a standard solution. The procedure of adding one solution to another in a measured way until the reaction is complete is called rtrnttion. Volumetric analysis is often referred to as titrimetrie nnulysis or titrimetry. 

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