Titration, 40, Also

Finally, quantitative problems involving multiple analytes and back titrations also can be solved by applying the principle of conservation of electron pairs. 

The scale of operations, accuracy, precision, sensitivity, time, and cost of methods involving precipitation titrations are similar to those described earlier in the chapter for other titrimetric methods. Precipitation titrations also can be extended to the analysis of mixtures, provided that there is a significant difference in the solubilities of the precipitates. Figure 9.43 shows an example of the titration curve for a mixture of % and Ch using Ag+ as a titrant. 

Titrimetric Methods. Frequently, the reduction of gold solutions leads to finely divided precipitates which are difficult to recover quantitatively. In such cases, the reduction of Au(III) to Au(0) by, eg, hydroquinone, can be followed potentiometricaHy (49). The end point in such titrations also can be determined with indicators such as benzidine (50) or o-anisidine (51). Alternatively, the reduction can be effected with excess hydroquinone which is then back-titrated with Ce(IV) (52). lodometric deterrnination of Au(III) also is useflil (53). 

Beyond the buffer region, when nearly all of the acetic acid has been consumed, the pH increases sharply with each added drop of hydroxide solution. The titration curve passes through an almost vertical region before leveling off again. Recall from Chapter 4 that the stoichiometric point of an acid titration (also called the equivalence point) is the point at which the number of moles of added base is exactly equal to the number of moles of acid present in the original solution. At the stoichiometric point of a weak acid titration, the conjugate base is a major species in solution, but the weak acid is not. 

Phase diagrams of a polyacrylate-phosphonate system with temperature and calcium ion concentration can be established with turbidimetric measurements [1830]. Conductometric titrations also are suitable to characterize the phase behavior of scale inhibitors [514] (Table 7-2). 

What is the percent of CaC03 in an antacid given that a tablet that weighed 1.3198 g reacted with 50.00 mL of 0.4486 N HC1 that subsequently required 3.72 mL of 0.1277 N NaOH for back titration Also report the milligrams of CaC03 in the tablet. 

A back titration - also known as an indirect titration - allows the concentration of an unknown solution to be determined by reacting it with a known excess of a reagent. The quantity of the excess reagent is determined by titration with a second reagent. 

Elemental composition Ta 50.50%, Cl 49.50%. Tantalum content in an acid extract (HF-HNO3 extract) can be determined by various instrumental techniques. The pentachloride is hydrolyzed to HCl, which can be measured by acid-base titration. Also, the compound can be identified from its physical and x-ray properties. 

Elemental composition Ti 31.05%, Cl 68.95%. Because it is a strong reducing agent and its aqueous solution is stable, the trichloride can be measured by redox titration. Also, titanium can be analyzed by various instrumental methods after digestion in an acid. 

An advantage of the technique is the use of an electrical standard to replace chemical standards and the problems associated with their preparation and stability. The coulometric titration also permits the generation of reagents such as copper(I) or bromine, which are difficult to employ as standard solution, or others such as silver(II) or chlorine, which are virtually impossible to use in any other way. A disadvantage of the coulometric titration is its lack of specificity. 

The interaction of the linearly linked tris-cyclam derivative 13 with Ni(II), Cu(II), Zn(II), Cd(II), and Pd(II) has been investigated [32], As for the above tri-branched systems, all five metals yield solid complexes in which the metal ligand stoichiometry is 3 1 with, for Cu(II), a spectrophotometric titration also confirming the formation of a complex of this stoichiometry in acetonitrile. Cyclic voltammograms of both the Ni(II) (low-spin) and Cu(II) complexes both yield evidence for the presence of M(II)/M(III) as well as M(I)/M(II) couples in acetonitrile. 

The latex was cleaned by ion exchange and serum replacement, which gave the cleaned latex plus six serum fractions. The cleaned latex and the serum samples were analyzed by conductometric titration. Also, the amount of anionic emulsifier in the serum was determined by Fyamine 1622 colorimetric titration and thin-film chromatography, and the amount of nonionic emulsifier by iodine-iodide colorimetric titration and thin-film chromatography. 

Add solutions of polyelectrolytes simultaneously to drawing bath Stoichiometric product yield regardless of mixing ratio no purification of starting materials required Control of product addition rates difficult reactor mixing and product titration also troublesome 437... 

Surface tension measurement. Adsorption titration, also called soap titration, (2.3) was carried out by the drop volume method at different polymer concentrations. The equivalent concentration of salt was held constant. The amount of emulsifier necessary to reach the critical micelle concentration (CMC) in the latex was determined by each titration. The total weight of emulsifier present in the latex is the weight of emulsifier in the water plus the weight of emulsifier adsorbed. The linear plot of emulsifier concentration (total amount of emulsifier corresponding to the end-point of each titration) versus polymer concentration gives the CMC as the intercept and the slope determines the amount of emulsifier adsorbed on the polymer surface in equilibrium with emulsifier in solution at the CMC (E ). 

No single method for protein study gives much information by itself and spectrophotometric titrations also have been best exploited in conjunction with auxiliary studies. For example, Tanford has routinely coupled his studies with results obtained from electrometric H+-titration studies, to show with certainty that only part of the anomalous phenolic titration of proteins can be explained by a general electrostatic argument. The review by Tanford in this volume discusses these problems in detail. 

Das Gesamtvolumen betragt nach Zugabe der Natronlauge V = 29,6 mL. In der Vorlage befindet sich nach der Titration also folgende Stoffmenge an OIT(aq)-lonen ... 

This work has been undertaken as part of a program to add to our knowledge of the oxidation of CO over Pt via models based on elementary steps (refs.1,2,3,4). Here we measure the reaction of C0(g) with adsorbed oxygen, and 0 (g) with adsorbed CO. These processes, although not elementary steps, are simpler to analyze than the full reaction. In the present study we are concerned only with the amounts of adsorbed CO and oxygen. As such, the measurements are equivalent to the titration of one adsorbed species by the other gaseous species. We are particlarly interested in the effect of temperature. The fraction exposed (FE) of the Pt particles supported on Si0 (Cabosil) may have an effect on the titrations also. 

For this titration also, we must be more careful in choosing the indicator than for a strong acid-strong base titration. Phenolphthalein changes color too soon and too slowly to indicate the equivalence point on the other hand, methyl red lies on the steep portion of the curve and straddles the equivalence point, so it is a perfect choice. 

Despite this, potentiometric titration also presents some limitations, such as very slow establishment of the ion-exchange equilibria [85]. 

Potentiometric titration also presents some limitations such as a very slow establishment of the ion exchange equilibria. The sample s particle size and the rate of titration have been reported to affect the proton binding curve [205]. Nevertheless, under the optimized conditions, potentiometric titration is a viable and independent method, tliat provides a comprehensive and detailed description of acid-base chemistiy that occurs in carbon-aqueous electrolyte suspensions [205]. 

Instances of apparent oxidation sometimes occur that are actually attributable to analytical difficulties. Thus, 1 mol of methyl 2-deoxy-a-D-xj/o-hexopyranoside appears to consume 2 mol of periodate, not one, as measured by the arsenite method, because the methylene group of the oxidation product is iodinated during the back-titration. Also, some tridentate periodate complexes are decomposed only slowly by arsenite, resulting in spurious uptake values. " A 3,6-anhydro-... 

If, as good analytical practice demands, the standardization titration also contains the same amoimt of indicator solution as each of the determination runs, then the indicator errors will be almost negligible. 

However, there are instances when no visible indicator is available to identify the equivalence point of a titration. Also, some color changes can be very subtle, which can introduce subjectivity (and hence errors) in determining the equivalence point. In these situations, a more reliable detector than the human eye is required. In situations where the analyte, reagent, or titration product absorbs radiation, photometric measurements can be employed to determine the equivalence point of the titration. 

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