Volumetric Analysis Titration

Other than gravimetric analysis, the other major type of classical wet chemical analysis techniques consists of measuring the volume of a reagent required to react with an analyte. Such a procedure is called titration, which involves the following steps  

A measured quantity of sample that may consist of a weighed quantity of a solid, or a measured volume of a solution of the unknown, is placed in solution. 

A standard solution of known concentration of a reagent that reacts quantitatively with the analyte is added to the unknown with a burette so that the volume of the standard solution can be measured accurately. 

An indicator consisting of a dye that changes color, or some other means, is used to detect an end point, the experimental representation of the equivalence point at which exactly the stoichiometric amount of reagent required to react with the analyte occurs. The volume at which the end point occurs is recorded from the burette. 

The quantity or concentration of the analyte is calculated from the stoichiometry of the titration reaction. 

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Kolthoff, I.M. Belcher, R., Volumetric Analysis. Titration. Methods Oxidation Reduction Reaction. Interscience Publishers, Inc., NY 1957. Vol. Ill Koppenol, W.H. Liebman, J. J. Phys. Chem. 1984, 88, 99-101. 

Box 21.1 Types of calculations used in volumetric analysis - titrations... 

The most popular device for fluoride analysis is the ion-selective electrode (see Electro analytical techniques). Analysis usiag the electrode is rapid and this is especially useful for dilute solutions and water analysis. Because the electrode responds only to free fluoride ion, care must be taken to convert complexed fluoride ions to free fluoride to obtain the total fluoride value (8). The fluoride electrode also can be used as an end poiat detector ia titration of fluoride usiag lanthanum nitrate [10099-59-9]. Often volumetric analysis by titration with thorium nitrate [13823-29-5] or lanthanum nitrate is the method of choice. The fluoride is preferably steam distilled from perchloric or sulfuric acid to prevent iaterference (9,10). Fusion with a sodium carbonate—sodium hydroxide mixture or sodium maybe required if the samples are covalent or iasoluble. 

Thus the quantitative oxidation of 8203 " by I2 to form tetrathionate and iodide is the basis for the iodometric titrations in volumetric analysis... 

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. 

In a titration, the volume of one solution is known, and we measure the volume of the other solution required for complete reaction. The solution being analyzed is called the analyte, and a known volume is transferred into a flask, usually with a pipet. Then a solution containing a known concentration of reactant is measured into the flask from a buret until all the analyte has reacted. The solution in the buret is called the titrant, and the difference between the initial and the final volume readings of the buret tells us the volume of titrant that has drained into the flask. The determination of concentration or amount by measuring volume is called volumetric analysis. 

Attention is finally focused on the advantages of conductometric titrations, which include (i) colored solutions where no indicator is found to function satisfactorily can be successfully titrated by this method (ii) the method is useful for titrating weak acids against weak bases, which does not produce a sharp change in color with indications in ordinary volumetric analysis and (iii) more accurate results are obtained because of the graphical determination of the end-point. 

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. 

There is one other type of volumetric analysis that we will consider here back titrations. 

Potassium iodate is an oxiding agent in volumetric analysis. It releases iodine in KIO3-KI solutions for iodometric titrations. It also is a topical antiseptic and an additive to food to provide nutrient iodine. 

The proeess of obtaining quantitative information on a sample using a fast chemieal reaction by reacting with a certain volume of reactant whose concentration is known is called titration. Titration is also called volumetric analysis, which is a type of quantitative chemical analysis. Generally, the titrant (the known solution) is added from a burette to a known quantity of the analyte (the unknown solution) until the reaction is complete. From the added volume of the titrant, it is possible to determine the concentration of the unknown. Often, an indicator is used to detect the end of the reaction, known as the endpoint. 

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. 

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 validity of an analytical result depends on knowing the amount of a primary standard. A solution with an approximately desired concentration can be standardized by titrating a primary standard. In a direct titration, titrant is added to analyte until the reaction is complete. In a back titration, a known excess of reagent is added to analyte, and the excess is titrated with a second standard reagent. Calculations of volumetric analysis relate the known moles of titrant to the unknown moles of analyte. 

The peroxide value (PV) of an oil or fat is defined as the quantity of peroxide oxygen present in the sample. This classical iodometric method is a volumetric analysis based on the titration of iodine released from potassium iodide by peroxides in a biphasic system using a standardized thiosulfate solution as the titrant and a starch solution as the indicator (see Background Information, discussion of peroxide value). This method will detect all substances that oxidize potassium iodide under the acidic conditions of the test, therefore the purity of the reagents is critical. 

Titration A method of volumetric analysis in which a volume of one reagent (for example an acid) is added to a known volume of another reagent (for example an alkali) slowly from a burette until an end-point is reached. If an acid and alkali are used, then an indicator is used to show that the end-point has been reached. 

The results shown in Fig. 15.4 are very interesting like the titration curve in the volumetric analysis, there is a mutation point on the pH curve of the reaction mixture versus the amount of aqua ammonia added. This is opposite to the property of a buffer solution. 

In volumetric analysis, hydrophilic colloids alter the end point, e.g., in a titration of HC1 and NaOH, the amount of deviation in the end point is increased with increasing amounts of colloids. In the volumetric estimation of silver by Mohr s method, the phenomenon of adsorption comes into being. 

Pure ferric oxide is recommended for the standardising of permanganate solutions for volumetric analysis. It is dissolved in hydrochloric acid, reduced with stannous chloride, and titrated with permanganate.11... 

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