Titration argentometric

Argentometric titrations may be divided into two broad categories, namely (/ ) Direct titration with silver-nitrate, and... 

Elemental composition Ca 36.11%, Cl 63.89%. An aqueous solution of the compound may be acidified and analyzed for calcium by AA or ICP methods (see Calcium). The solution may be analyzed for chloride ion by ion selective electrode, ion chromatography or by argentometric titration. 

Potassium chromate is used in enamels rustproof metals and leather finishes. The compound also is an indicator in argentometric titrations. 

Silver chromate is a catalyst in conversion of alcohol to aldol. It s formation signals the end point in argentometric titration in measuring halides. 

End-point detection for precipitation titrations commonly relies on electrodes las in Figure 7-9) or indicators. This section discusses two indicator methods applied to the titration of Cl-with Ag+. Titrations with Ag4 are called argentometric titrations. 

In all argentometric titrations, but especially with adsorption indicators, strong light (such as daylight through a window) should be avoided. Light decomposes silver salts, and adsorbed indicators are especially light sensitive. 

Applications of precipitation titrations are listed in Table 7-1. Whereas the Volhard method is an argentometric titration, the Fajans method has wider applications. Because the Volhard titration is carried out in acidic solution (typically 0.2 M HN03), it avoids certain interferences that affect other titrations. Silver salts of CO -, C20 -, and AsO " are soluble in acidic solution, so these anions do not interfere. 

Mohr titration Argentometric titration conducted in the presence of chromate. The end point is signaled by the formation of red Ag2Cr04(.v). molality A measure of concentration equal to the number of moles of solute per kilogram of solvent. 

A mixture of 15 (4.2 g, 20 mmol), powdered Zn (14.5 g, 0.22 mol), H20 (15 mL), and 5 M NaOH (6.6 mL) was refluxed with stirring forca. 1.5 h(the progress of the reaction was followed by argentometric titration). The zinc was filtered off by suction, the oily layer was separated, and unreacted zinc was washed with EtOH (3 x 10 mL). The aqueous filtrate was extracted with benzene (3x10 mL) and the extract was mixed with the oil and EtOH washings. All solvents were removed in vacuo to give the crude product (2.5 g) that was purified by distillation to give pure 16 yield 2.2 g (72%) bp 97-100 C/l7 Torr. 

Argentometric titration involves the titrimetric determination of an analyte using silver nitrate solution as titrant. Its application in environmental analysis is limited to the determination of chloride and cyanide in aqueous samples. The principle of the method is described below. 

Ag+ preferentially reacts with the analyte to form a soluble salt or complex. During this addition, Ag+ reacts with the analyte only, and not the indicator. But when all the analyte is completely consumed by Ag+ and no more of it is left in the solution, addition of an excess drop of silver nitrate titrant produces an instant change in color because of its reaction with the silver-sensitive indicator. Some of the indicators used in the argentometric titrations are potassium chromate or dichlorofluorescein in chloride analysis and p -dime thy la m i nobe nzalrho da n i nc in cyanide analysis. Silver nitrate reacts with potassium chromate to form red silver chromate at the end point. This is an example of precipitation indicator, where the first excess of silver ion combines with the indicator chromate ion to form a bright red solid. This is also known as Mohr method. 

Another class of indicators, known as adsorption indicators, adsorb to (or desorb from) the precipitate or colloidal particles of the silver salt of the analyte at the equivalence point. The indicator anions are attracted into the counterion layer surrounding each colloidal particle of silver salt. Thus, there is a transfer of color from the solution to the solid or from the solid to the solution at the end point. The concentration of the indicator, which is an organic compound, is not large enough to cause its precipitation as a silver salt. Thus, the color change is an adsorption and not a precipitation process. Fluorescein is a typical example of an adsorption indicator in argentometric titration. 

To analyze sulfide (S2 ) in an aqueous sample, 150 mL of sample was made ammoniacal before argentometric titration. The sample required 10.45 mL of 0.0125 M AgN03 solution in the titration. Determine the concentration of the sulfide in the sample. 

Precipitation titrimetry — A method for the - titration of species by a - precipitation reaction. Commonly, the - end point of precipitation reactions is monitored by chemical, potentiometric or amperometric methods. A chemical method involves an -> indicator that usually has a change in color at the -> endpoint, while the other methods can be implemented as a -> potentiometric titration or -> amperometric titration, respectively. An important precipitating reagent is silver nitrate, i.e., silver ions Ag+. Such titrations are called argentometric titrations [i], and silver - electrodes are useful as indicator electrodes. 

The consumption of cyanide is accurately determined by argentometric titration. The method was found to apply both to oxidized starch [439] as well as to cellulose [418], The method is accurate and recently the coefficient of variance and standard deviation for an oxidized cellulose containing 5.60 mmol per 100 g of ketone groups, were found to be 0.0046 and 0.0068, respectively. The corresponding values for the carboxyl groups by the methylene blue method of the same samples were 0.001 and 0.031 [440]. 

The procedure was applied to additional dipeptides, and the course of the alkylation at 35-40°C followed by argentometric titration (Toennies and Kolb, 1945a). With over 90% formation of carbamylmethylsulfonium salts only 8% of peptide cleavage occurred at 40°C however, on brief heating at 95°C the yields of liberated amino acid increased to 54-85 % (Table XVI). Paper chromatography and paper electrophoresis of such reaction mixtures showed that in each case the hberated amino acid was the only ninhydrin-positive substance present. 

Argentometric titration method has been applied to the determination of sulfonamide mixtures. The sulfonamides are quantitatively precipitated by the addition of excess standard silver nitrate solution, the precipitated silver salts removed by filtration, and the excess silver nitrate titrated with standard ammonium thiocyanate using ferric alum as indicator (32). 

The homogeneity of the material for its matrix composition was verified for the elements Cl, S, Ca, K and P. Chlorine was determined after an oxygen flask combustion by an argentometric titration with potentiometric detection sulphur was determined... 

For F and Cl, the techniques used were mainly based on oxygen combustion, pyrohydrolysis or fusion with Na2C03 followed by ion selective electrode or ion chromatography. Neutron activation analysis with fast neutrons was also used by one laboratory for F, as well as visible light spectrometry the latter technique was also used for Cl as well as argentometric titration. A detailed description of the methods is given in the certification report [13],... 

For chlorine, low results obtained with HNO, addition were suspected to be due to an incomplete dissolution (leaching of Cl rather than attack) which justified the rejection of one set of results. Chlorine was certified on the basis of 10 sets of results (8 IC, 1 SPEC and 1 argentometric titration). The certified value is (323 22) mg kg. ... 

EDAT Eschka digestion followed by argentometric titration... 

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