Chloride titrators

Addition of silver nitrate to a solution of a chloride in dilute nitric acid gives a white precipitate of silver chloride, AgCl, soluble in ammonia solution. This test may be used for gravimetric or volumetric estimation of chloride the silver chloride can be filtered off, dried and weighed, or the chloride titrated with standard silver nitrate using potassium chromate(VI) or fluorescein as indicator. 

Assay Methods. A Na carbonate fusion prod is currently used for assay of mil grade AP (see below under Specifications), but recently attempts have been made to replace it with a method which is faster and simpler to carry out. Two procs have been proposed a) Titanous Chloride Titration. A measured excess of Ti trichloride is added to a known weight of AP which reacts according to the equation ... 

Salt Rejection The salt rejection of the membrane was calculated from the chloride contents of the feed, and product as measured by chloride titration(Aminco Cotlove, Silver Springs). The apparent salt rejection R j is defined as ... 

Salt (NaCl) AOAC 975.20 (2005) Quantab strip chloride titration method (based on Mohr s titration)... 

The above reaction, however, is less favorable than the former reaction. Therefore, K2Cr04 can indicate the end point of AgN03 chloride titration. At the end point, when no free chloride is left in the solution, addition of a drop of AgN03 titrant results in the formation of Ag2Cr04 producing a pink end point. 

Chloride Mercuric nitrate Chloride titration with mercuric ions Chromate, Fe3+, and S032- 50,52... 

A much simpler and more rapid chloride titration unit has been described by Cotlove et al. (Cl, see also LI). This or similar design has been commercially produced by a number of companies.17 The titration principle is that of a coulometric titration. In coulometric methods the titrant is prepared by electrolysis rather than added as a solution from a buret. 

Chloride titrator, American Instrument Co., Silver Springs, Maryland Coulo-matic titrimeter, Fisher Scientific Co., New York, New York. 

The use of automatic titrating devices is a subject of greater complexity. In the larger institutions, the acquisition of a single instrument (e.g. chloride titrator) limited to one test may very well be justified. The increased accuracy and saving of time alone could be ample reason for such a purchase. In the future, other tests may be adapted to electroanalysis. This could very well implement a decision to automate with any of the available automatic titrators. 

Titanous Chloride Titration Apparatus. .. 883 Allura Red-Top Trace Eluant Monitored at 254 nm Bottom Trace Eluant Monitored at 375 to 385 nm. .. 885... 

Figure 20-3. Potentiometric titration curve of chloride titrated with silver ion.

I)Chlorides. Add to ca a 10 g sample weighed to 0.1 mg in a porcelain casserole, ca 80 ml of 10% NaOH soln and boil until all ammonia is driven off. Dissolve the residue in ca 150 ml cold distd w, neutralize with nitric acid and add a slight excess of Ca carbonate (free from chlorides). Titrate with N/10 Ag nitrate soln, using K chromate as an indicator. Calculate the chlorides found to %-age of NH C1 in the sample Note If the amt of chlorides in Grade III AN is not above 0.02%, the following turbido-metric procedure may be used ... 

Curve A in Figure 13-6, which is the titration curve for the chloride/iodide mixture just considered, is a composite of the individual curves for the two anionic species. Two equivalence points are evident. Curve B is the titration curve for a mixture of bromide and chloride ions. Clearly, the change associated with the first equivalence point becomes less distinct as the solubilities of the two precipitates approach one another. In the bromide/chloride titration, the initial pAg values are lower than they are in the iodide/chloride titration because the solubility of silver bromide exceeds that of silver iodide. Beyond the first equivalence point, however, where chloride ion is being titrated, the two titration curves are identical. 

A number of instrument manufacturers offer automatic coulometric titrators, most of which employ a potentiometric end point. Some of these instruments are multipurpose and can be used for the determination of a variety of species. Others are designed for a single type of analysis. Examples of the latter are chloride titrators, in which silver ion is generated coulometrically sulfur dioxide monitors, where anodically generated bromine oxidizes the analyte to sulfate ions carbon dioxide monitors, in which the gas, absorbed in monoethanolamine, is titrated with coulometrically generated base and water titrators, in which Karl Fischer reagent (see Section 20C-5) is generated electrolytically. 

The potentiometric technique involves the use of glass, ISE and platinum electrodes, the latter used in connection with nearly all oxidation-reduction titrations. These electrodes use external or internal reference electrodes. In the main, the reference is an Ag/AgCl (3M KCl) unit with an outer compartment capable of being filled with an electrolyte of choice and changeable. For chloride titrations, for example, the indicator electrode is often a silver billet coated with AgCl, with a Ag/AgCl reference 3M KNO3 filled. 

Undoubtedly, these methods have their special merits and possibilities. However, it is wise to consider if the purchase of expensive apparatus is justified by increased accuracy and/or speed. In the case of the chloride titration, for instance, it is the writers experience that the ultramicro titration according to Schales and Schales (S4) can be performed with nearly the same accuracy, reproducibility, standard deviation, and speed as is achieved potentiometricaUy. 

If the chloride titration were performed in reverse, that is, Ag titrated with Cl", the titration curve would be the reverse of the curve in Figure 11.1 if pCl were plotted against the volume of Cl". Before the equivalence point, the Cl" concentration would be governed by the concentration of excess Ag" " and and beyond the equivalence point, it would be governed merely by the excess Cl". The pAg value could be plotted, instead, against the volume of chloride solution, and the curve would look the same as that of Figure 11.1. 

Prepare a spreadsheet to plot the titration curve of 100 mL 0.1 M chloride titrated with 0.1 M silver nitrate (Figure 11.1). See your CD for a suggested setup. Use the spreadsheet to change the concentrations of chloride and silver (e.g., 0.2 M each, 0.05 M each), and notice how the titration curve changes. Note that there is a limit to how low the concentrations can go in these calculated plots because eventually the solubility of the AgCl at 99.9 and 100.1 mL titrant becomes appreciable. 

Owing to metal chlorides titration by the coulometric method, and carboxylic acid titration by the potentiometric method, it is possible to follow the metal soaps consumption during thermomechanical heat treatments. This new technique provides a better understanding of the stabilization mechanisms of PVC with the calciumr-zinc system, and offers a better explanation of synergistic effects between metal soaps and secondary stabilizers such as epoxidized soya-bean oil, a-phenylindole, and butanediol-p-aminocroto-nate. The influence of these last stabilizers on zinc chloride formation enables us to classify them into short- and longterm stabilizers. 

For each stabilizing system we have drawn the total amount of transformed carboxylates versus heating time from metal chloride titration (Curve 1) or stearic acid titration (Curve 2), according to the stoichiometry of Reaction 1 (Figures 1, 2, and 3). Curves 1 and 2 would be superposed on each figure if the stabilizer consumption was caused only by Reaction 1 however, experimentally they are not. 

For zinc and calcium-stearate mixture, there is always an excess of transformed stearate from stearic acid titration with respect to metal chlorides titration during gelation of plasticized PVC in the Brabender plasticorder (area 1-3 on the plastogram, and Curves 1 and 2 on Figure... 

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