Titrimetric solutions, standard

Sodium Oxalate. This salt [62-76-0], Na2C204, mol wt 134.01, is obtained in such high purity and is so stable that it is used as a titrimetric standard. The salt is not very soluble in water the saturated solution contains 2.6 wt % and 6.1 wt % Na2C204 at 0°C and 100°C, respectively. 

In titrimetric analysis (often termed volumetric analysis in certain books), the substance to be determined is allowed to react with an appropriate reagent added as a standard solution, and the volume of solution needed for complete reaction is determined. The common types of reaction which are used in titrimetry are (a) neutralisation (acid-base) reactions (b) complex-forming reactions (c) precipitation reactions (d) oxidation-reduction reactions. 

One of the commonest procedures carried out by the analyst is the measurement of mass. Many chemical analyses are based upon the accurate determination of the mass of a sample, and that of a solid substance produced from it (gravimetric analysis), or upon ascertaining the volume of a carefully prepared standard solution (which contains an accurately known mass of solute) which is required to react with the sample (titrimetric analysis). For the accurate... 

The term titrimetric analysis refers to quantitative chemical analysis carried out by determining the volume of a solution of accurately known concentration which is required to react quantitatively with a measured volume of a solution of the substance to be determined. The solution of accurately known strength is called the standard solution, see Section 10.3. The weight of the substance to be determined is calculated from the volume of the standard solution used and the chemical equation and relative molecular masses of the reacting compounds. 

The word concentration is frequently used as a general term referring to a quantity of substance in a defined volume of solution. But for quantitative titrimetric analysis use is made of standard solutions in which the base unit of quantity employed is the mole. This follows the definition given by the International Union of Pure and Applied Chemistry1 in which ... 

The most important advantage of the equivalent system is that the calculations of titrimetric analysis are rendered very simple, since at the end point the number of equivalents of the substance titrated is equal to the number of equivalents of the standard solution employed. We may write ... 

Titrimetric analysis - continued general discussion of, 257 primary and secondary standards for, 261 storage and preservation of solutions, 108 technique of, 286... 

A titrimetric method involves the controlled reaction of a standard reagent in known amounts with a solution of the analyte, in order that the stoichiometric or equivalence point for the reaction between the reagent and the analyte may be located. If the details of the reaction are known and the stoichiometric point is located accurately and precisely, the amount of analyte present may be calculated from the known quantity of standard reagent consumed in the reaction. In most cases a standard reagent solution is prepared and added manually or automatically from a burette an alternative procedure is coulometric generation of the reagent in situ. The stoichiometric point may be detected by use of a visual indicator or by an electrochemical method (Chapter 6). 

We will now consider the preparation of solutions. Solutions are prepared for a wide variety of reasons. We have already discussed the use of standard solutions in titrimetric analysis and that these solutions sometimes must be prepared with high precision and accuracy so that their concentrations may be known directly through the preparation process. Even if the need for good precision and accuracy through the preparation is not necessarily important, an analyst frequently prepares other solutions with concentrations known less precisely. Thus the familiarity with solution preparation schemes, highly precise or not, is very important. 

In titrimetric analysis (Figure 6.3), a weight or volume of the prepared sample is needed and the sample may need to be dissolved or otherwise pretreated following the weight or volume measurement. The most important part, however, is that a standard solution (the titrant) needs to be prepared and standardized. This solution is used to titrate the sample, and the buret reading is the datum needed for calculating the results. 

For gravimetric analysis, a solution may be needed to react with the analyte. Otherwise it consists of just physical separation operations and usually initial and final weight measurements. For titrimetric analysis, solutions are always needed to react with the analyte and these solutions must be standardized. Also, a critical measurement is a volume measurement (buret reading). 

Detection, identification and quantification of these compounds in aqueous solutions, even in the form of matrix-free standards, present the analyst with considerable challenges. Even today, the standardised analysis of surfactants is not performed by substance-specific methods, but by sum parameter analysis on spectrophotometric and titrimetric bases. These substance-class-specific determination methods are not only very insensitive, but also very unspecific and therefore can be influenced by interference from other compounds of similar structure. Additionally, these determination methods also often fail to provide information regarding primary degradation products, including those with only marginal modifications in the molecule, and strongly modified metabolites. 

Titrimetric methods also measure gold in solution. Gold(llI) may be reduced by excess hydroquinone which may be back titrated with a standard solution of cerium(lV) titrant. (4old(lll) may also be determined by iodometric titration. 

Titrimetric measurement involves titrating alkaline HCN solution against a standard solution of silver nitrate using a silver sensitive indicator, p-... 

Measurement of Reaction Rates by Titrimetry. The rates of cerium(IV) consumption by each of Cr(C204)3 3, m-Cr(OH2)2(C204)2 and Cr(0H2)4C204+ were also measured by a direct titrimetric method. Solutions were prepared and mixed as for the spectrophotometric procedure. At appropriate times aliquots of the reactant solutions were quenched with known volumes of standard ferrous sulfate, and the excess ferrous ion was titrated potentiometrically with standard potassium dichromate,... 

A modification of this method is to effect the oxidation by a known quantity of bromine (obtained by the addition of standard potassium bromate solution together with potassium bromide and hydrochloric acid) and subsequently add excess of potassium iodide the superfluous bromine liberates a corresponding amount of iodine, which can be estimated titrimetrically hence the bromine consumed and the hydrogen sulphide oxidised can be calculated.4 The chemical change in this case is ... 

Analytical methods employed in soil chemistry include the standard quantitative methods for the analysis of gases, solutions, and solids, including colorimetric, titrimetric, gravimetric, and instrumental methods. The flame emission spectrophotometric method is widely employed for potassium, sodium, calcium, and magnesium barium, copper and other elements are determined in cation exchange studies. Occasionally arc and spark spectrographic methods are employed. 

In general, any titrimetric procedure involves slow addition of a solution of accurately known concentraion (a standard solution) to a solution of unknown concentration (sample to be analyzed) until the reaction between both the solutions is complete. In other words, the standard titrant is added slowly up to the point known as end point at which the solute analyte in the sample is completely consumed by the solute in the standard solution. The completion of the reaction is usually monitored by using an indictor, which causes a color change at the end point. 

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