Quantitative analysis Acid-base titrations

A double end point, acid—base titration can be used to determine both sodium hydrosulfide and sodium sulfide content. Standardized hydrochloric acid is the titrant thymolphthalein and bromophenol blue are the indicators. Other bases having ionization constants in the ranges of the indicators used interfere with the analysis. Sodium thiosulfate and sodium thiocarbonate interfere quantitatively with the accuracy of the results. Detailed procedures to analyze sodium sulfide, sodium hydro sulfide, and sodium tetrasulfide are available (1). 

An analytical solution for molecules with alkaline functionality is acid/base titration. In this technique, the polymer is dissolved, but not precipitated prior to analysis. In this way, the additive, even if polymer-bound, is still in solution and titratable. This principle has also been applied for the determination of 0.01 % stearic acid and sodium stearate in SBR solutions. The polymer was diluted with toluene/absolute ethanol mixed solvent and stearic acid was determined by titration with 0.1 M ethanolic NaOH solution to the m-cresol purple endpoint similarly, sodium stearate was titrated with 0.05 M ethanolic HC1 solution [83]. Also long-chain acid lubricants (e.g. stearic acid) in acrylic polyesters were quantitatively determined by titration of the extract. 

Titrations are veiy powerful techniques that contain two very different kinds of information and thus serve two different purposes (a) titrations are used for quantitative analytical applications, e.g. the determination of the concentration of an acid by an acid-base titration or the determination of a metal ion by a complexometric titration (b) titrations serve also as a method for the determination of equilibrium constants, e.g. the determination of the strength of the interaction between a metal ion and a ligand. Naturally, both objectives can be combined and the analysis of one titration can deliver both types of information. 

An acid-base titration is a method that allows quantitative analysis of the concentration of an unknown acid or base solution. In an acid-base titration, the base will react with the weak acid and form a solution that contains the weak acid and its conjugate base until the acid is completely neutralized. The following equation is used frequently when trying to find the pH of buffer solutions. 

The normality of a solution of an acid or base is the number of equivalents of acid or base per liter a 1 solution contains 1 equivalent per liter of solution. By determining, with use of an indicator, such as litmus, the relative volumes of acidic and alkaline solutions which are equivalent the normality of one solution can be calculated from the known value of the other. This process of acid-base titration (the determination of the titer or strength of an unknown solution), with use of special apparatus such as graduated burets and pipets, is an important method of volumetric quantitative analysis. 

NB differing values in Merck Index (4.35), Foye (9.25), Connors et al. (9.8 at 18 C 10.2 at 16.5 C). There is confusion here between pKi, and pKa values, especially die Merck value. The value of 5.93 comes from Medwick T, Kaplan G, Weyer LG, Measurement of acidity and equilibria in glacial acetic acid widi the glass calomel electrode system, /. Pharm. Sci., 58,308-313 (1969) see also Bases (nonaqueous titrations). This value is mainly relevant to quantitative analysis by nonaqueous titration. 

C Q Yang, G D Bakshi, Quantitative Analysis of the Nonformaldehyde Durable Press Finish on Cotton Fabric Acid-Base Titration and Infrared Spectroscopy", Textile ResJ, 1996 66(6)377-384... 

An acid-base titration is a quick and convenient method for the quantitative analysis of substances with acidic or basic properties. Many inorganic and organic acids and bases can be titrated in aqueous media, but others, mainly organic, are insoluble in water. Fortunately, most of them are soluble in organic solvents hence they are conveniently determined by nonaqueous acid-base titrimetry. Although acid-base titrations can usually be followed potentio-metrically, visual endpoint detection is quicker and can be very precise and accurate if the appropriate indicator is chosen. 

Acid-base titration The quantitative analysis of the amount or concentration of an acid or base in a sample by observing its reaction with a known amount or concentration of a base or acid. 

Certain aqueous reactions are useful for determining how much of a particular substance is present in a sample. For example, if we want to know the concentration of lead in a sample of water, or if we need to know the concentration of an acid, knowledge of precipitation reactions, acid-base reactions, and solution stoichiometry will be useful. Two common types of such quantitative analyses are gravimetric analysis and acid-base titration. 

In Section 4.6 we introduced acid-base titrations as a form of chemical analysis. Having discussed buffCT solutions, we can now look in more detail at the quantitative aspects of acid-base titrations. We will consid - three types of reactions (1) titrations involving a strong acid and a strong base. 

Selecting and Standardizing a Titrant Most common acid-base titrants are not readily available as primary standards and must be standardized before they can be used in a quantitative analysis. Standardization is accomplished by titrating a known amount of an appropriate acidic or basic primary standard. 

Quantitative Analysis of All llithium Initiator Solutions. Solutions of alkyUithium compounds frequentiy show turbidity associated with the formation of lithium alkoxides by oxidation reactions or lithium hydroxide by reaction with moisture. Although these species contribute to the total basicity of the solution as determined by simple acid titration, they do not react with allyhc and henzylic chlorides or ethylene dibromide rapidly in ether solvents. This difference is the basis for the double titration method of determining the amount of active carbon-bound lithium reagent in a given sample (55,56). Thus the amount of carbon-bound lithium is calculated from the difference between the total amount of base determined by acid titration and the amount of base remaining after the solution reacts with either benzyl chloride, allyl chloride, or ethylene dibromide. 

A primary goal of this chapter is to learn how to achieve control over the pH of solutions of acids, bases, and their salts. The control of pH is crucial for the ability of organisms—including ourselves—to survive, because even minor drifts from the optimum value of the pH can cause enzymes to change their shape and cease to function. The information in this chapter is used in industry to control the pH of reaction mixtures and to purify water. In agriculture it is used to maintain the soil at an optimal pH. In the laboratory it is used to interpret the change in pH of a solution during a titration, one of the most common quantitative analytical technique. It also helps us appreciate the basis of qualitative analysis, the identification of the substances and ions present in a sample. 

The first question is what kind of information the chemical control can and should provide. Must it be a qualitative and/or quantitative analysis, is it based on a one- or two-dimensional measurement and should the latter consist of an analog and/or digital display The meaning of all this can be well illustrated by the example of the differential titration (see Fig. 5.1) of equivalent amounts of a strong acid (cf., Fig. 2.17, AA) and a weak acid (cf., Fig. 2.18, BA, pK, = 4). 

Quantitative Analysis of Alkyllithium initiator Solutions. The amount of carbon-bound lithium is calculated from the difference between the tolal amount of base determined by acid titration and the amount of base remaining after the solution reacts with either benzyl chloride, ally I chloride, or ethylene dibromide. 

Titration — A process for quantitative analysis in which measured increments of a - titrant are added to a solution of an - analyte until the reaction between the analyte and titrant is considered as complete at the - end point [i]. The aim of this process is to determine the amount of an analyte in a -> sample. In addition, the determination can involve the measurement of one or several physical and/or chemical properties from which a relationship between the measured parameter/s and the concentration of the analyte is established. It is also feasible to measure the amount of a - titrand that is added to react with a fixed volume of titrant. In both cases, the -> stoichiometry of the reaction must be known. Additionally, there has to be a means such as a -> titration curve or an - indicator to recognize that the -> end point has been reached. The nature of the reaction between the titrant and the analyte is commonly indicated by terms like acid-base, complexometric, redox, precipitation, etc. [ii]. Titrations can be performed by addition of measured volume/mass increments of a solution,... 

Anyone who has taken a course in quantitative analysis will tell you about repeating an experiment over and over again to get a large sample of data. It s not uncommon for experiments requiring a titration to be repeated anywhere from 7 to 10 times Once a number of experiments have been completed, you then want to compare the results to see if they are both accurate and precise. Accuracy is the term used to define how close the data have come to the accepted value. Precision is the term used to define how closely the data agree with data obtained from other performances of the same experiment. Hopefully your data will be both accurate and precise. Look at the following data a student obtained from a titration experiment involving an acid and base ... 

Oxyacids, like citric or tartaric acids, and polyols, like saccharose are also used, mainly as masking agents, in qualitative analysis. The action of some specific reagents, like oc-a -bipyridyl for iron(II) and dimethylglyoxime for nickel(II), is also based on the formation of chelate complexes. In quantitative analysis the formation of chelates is frequently utilized (complexometric titrations). ... 

In a chemical analysis, especially involving quantitative analysis, the amount of chemical used is critical and can be determined by the measurement of concentration if it is a solution, or by weight, if it is a solid. Sometimes, the concentration of a solution can be easily determined by using another known solution through titration. For acids and bases, if the concentration is sufficiently low, the pH concept is generally used to represent the concentration of the acid or base in the aqueous solution. For the analysis of common chemicals, such as caustic soda, acetic acid, soda ash, sodium dithionite, hydrogen peroxide, and so on, titrimetric analysis and gravimetric analysis are widely used. For the analysis of surfactants and other chemicals, qualitative spot tests and specialised instruments should be utilised. 

Important solution reactions are well known from the study of quantitative analysis in analytical chemistry. These include acid-base reactions, redox reactions, and complex formation reactions. Often the reaction is so fast that the system is considered to come instantaneously to equilibrium, for example, in the acid-base reaction involved in a titration. In fact, any of these reactions has a finite rate whose kinetics can be determined using modern experimental techniques. 

In this chapter we have applied the methods of chapter 4 to ionic equilibria other than those between acids and bases. Of course, complexation, extraction, solubility, precipitation, and redox equilibria may also involve acid-base equilibria, which is why we treated acid-base equilibria first. The examples given here illustrate that the combination of exact theory with the computational power of a spreadsheet allows us to solve many problems that occur in quantitative chemical analysis, and to analyze experimental data accordingly. Even quite complicated titrations, such as the multi-component precipitation titrations, the von Liebig titration, and redox titrations involving many species and complicated stoichiometries, can be handled with ease. 

Analytical chemistry has found great utility in conductimetric measurements in spite of its apparent nonspecificity. Rapid quantitative accuracy of a few tenths of a percent may be quickly accomplished by direct conductimetric determination of binary electrolytic solutions such as aqueous acids, bases, or salts. A nearly linear increase in conductivity is observed for solutions containing as much as 20% of solute. The concentration of strong solutions, such as the salinity of seawater, may be determined from conductance measurements traces of electrolyte impurities, such as the impurity in ultrapure water, may be reported at the pgl level. Conductimetric titrations may increase the accuracy of endpoint detection and permit titrimet-ric analysis of weak electrolytes, such as boric acid, which is not feasible by potentiometric or colorimetric... 

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