Mixtures potentiometric titration

A potentiometric titration is used to determine if an unknown sample is pure Na2G03, a mixture of Na2G03 and NaHG03, pure Na3P04, or a mixture of Na3P04 and Na2HP04. 

The titration of a mixture ofp-nitrophenol (pfQ = 7.0) and m-nitrophenol pK = 8.3) can be followed spectrophotometrically. Neither acid absorbs at a wavelength of 545 nm, but their respective conjugate bases do absorb at this wavelength. The m-nitrophenolate ion has a greater absorbance than an equimolar solution of the p-nitrophenolate ion. Sketch the spectrophotometric titration curve for a 50.00-mL mixture consisting of 0.0500 M p-nitrophenol and 0.0500 M m-nitrophenol with 0.100 M NaOH, and compare the curve with the expected potentiometric titration curves. 

Consequent potentiometric titration of osmium(IV) and laithenium (IV) in their mixtures has been canied out in broad range of concentrations from 1 mkg to 200 mkg in samples of 20 ml. It has been shown the possibility of amperemetric determination of osmium(VI) in binary and triple systems with silver(I), platinum(IV), palladium(II), gold(III), founded on formation of corresponding compounds with dimerkaptotiopiron, having a different solubility. The deteriuination of Os(VI) is possible under tenfold - hundredfold excess of above mentioned metals. 

Pyrolusite. Dissolve 1.5-2 g, accurately weighed, pyrolusite in a mixture of 25 mL of 1 1 hydrochloric acid and 6 mL concentrated sulphuric add, and dilute to 250 mL. Filtration is unnecessary. Titrate an aliquot part containing 80-100 mg manganese add 200 mL freshly prepared, saturated sodium pyrophosphate solution, adjust the pH to a value between 6 and 7, and perform the potentiometric titration as described above. 

The chlorine content can be determined by either chlorine elemental analysis or a potentiometric titration using a chloride-ion electrode. For titration, about 0.2 g. of polymer is heated in 3 ml. of pyridine at 100° for 2 hours. This suspension is then transferred to a 50-mi. beaker containing 30 ml. of aqueous 50% acetic acid and 5 ini. of concentrated nitric acid, and the resulting mixture is titrated against aqueous 0.1 N silver nitrate. 

A sample of polyester (ca. 1 g, exactly weighed) is dissolved in 20 mL toluene-ethanol mixture (1/1 vol.) and titrated by a solution of KOH in ethanol (0.05 mol/L) using a potentiometric titrator. A blank titration must be performed under the same conditions. Hardly soluble polyesters (e.g., PET) must be dissolved in an o-cresol-chloroform mixture or in hot benzyl alcohol.417 The result (acid content) is normally expressed in mmol COOH/g polyester but may also be given as the acid number, defined as the number of milligrams of KOH required to neutralize 1 g of polyester. [Acid number = (number of mmol COOH/g polyester) x 56.106.]... 

Kimura and co-workers have synthesized a series of alkoxide complexes with the alcohol functionality as a pendent arm.447 674 737 A zinc complex of l-(4-bromophenacyl)-l, 4,7,10-tetraaza-cyclododecane was also synthesized by the same workers to mimic the active site of class II aldolases. The X-ray structure shows a six-coordinate zinc center with five donors from the ligand and a water molecule bound. The ketone is bound with a Zn—O distance of 2.159(3) A (Figure 12). Potentiometric titration indicated formation of a mixture of the hydroxide and the enolate. Enolate formation was also independently carried out by reaction with sodium methoxide, allowing full characterization.738... 

The British Pharmacopoeia [2] describes a potentiometric titration method for the determination of penicillamine as the pure drug substance. The method is performed by dissolving 100 mg of the substance in 30 mL of anhydrous acetic acid. The mixture is titrated with 0.1 M perchloric acid, and the endpoint determined potentiometrically. Each milliliter of 0.1 M perchloric acid is equivalent to 14.92 mg of C6HnN02S. 

In the course of work on the potentiometric titration of some oxidizing acids, Malaprade1 found the existing method for determination of periodic acid in periodic-iodic acid mixtures too inaccurate for estimation of small proportions of one component. He discovered that mannitol will reduce only the periodic acid and, furthermore, that it only reduces the acid to iodic acid.2 The following general reaction appeared to take place. 

To conduct meaningful mechanistic and kinetic studies in alcohol media reliable and simple measurement and control of the solution jjpH is essential. Potentiometric titration is the method of choice for obtaining acid dissociation constants or metal ion complex stability constants and in favorable cases the speciation of mixtures of metal-ion-containing complexes in solution can be proposed.20 Titrations in non-aqueous solvents are not nearly as widely reported as those in aqueous media, particularly in cases with metal ions21 and determination of pH in a non-aqueous solvent referenced to that solvent is complicated due to the lack of a way to relate the electrode EMF readings to absolute jjpH (see footnote and ref. 6) so non-aqueous solvents are generally inconvenient to use22 for detailed studies of reaction mechanisms where pH control is required. 

Networks Applied to Potentiometric Titration of Multi-Component Polybasic Acid Mixtures. 

Asahi et al. have determined procaine hydrochloride by potentiometric titration with perchloric acid in a mixture of acetic anhydride and anhydrous acetic acid [89]. Procaine was determined by titration in acetic anhydride. 

In potentiometric titration a voltage is obtained from an electrode that is sensitive to an ionic species such as H-jO+, i.e., the pH of the solution in this case. We will consider the titration of the mixture of a strong acid (HC1) and a weak acid (CJ+jCOOH) with NaOH (ref. 10). As 2 ml volumes of the base are given to the acidic solution, the pH increases and when one of the acids is neutralized the pH changes very rapidly by a small addition of NaOH. We want to find these maximum points of the first derivative of the titration curve. In the following main program the DATA lines contain 32 data pairs, each consisting of the volume of the added NaOH in ml and the measured pH. 

Fig. 3.7 Potentiometric titration curve of a mixture of acids in MIBK [21]. Titrated with 0.2 M Bu4NOH using a glass electrode-Pt electrode system.

Allan S. Hay During the autoxidation of p-xylene catalyzed by cobalt acetate bromide, a potentiometric titration for bromide ion of an aliquot of the reaction mixture at 0°C. shows that only a fraction of the bromide is present in ionic form. If the titration is performed at room temperature, there is a gradual drift of the end point until it finally corresponds to the calculated total amount of bromide. The implication thus is that benzylic bromides are present during the reaction, and at room temperature during the titration they are slowly solvolyzed. 

There are numerous ways to determine experimentally pK values of chemical compounds (205). Classical methods are potentiometric titration and ultraviolet (UV) spectroscopy, among others. These techniques have been widely applied for nucleobases and also for metal-nucleobase complexes. For the extremes such as negative pK values (pK < —2) of singly or multiply protonated nucleobases, or very high pK values (pK >15) for deprotonation of exocyclic amino groups of nucleobases (C, G, A), modifications have to be employed. These include the consideration of the Hammett acidity function in superacidic solvents or solvent mixtures (206), as well as extrapolative techniques according to Bunnett-Olsen and Marziano-Cimino-Passerini to be applied in polar, aprotic solvents (45, 207). 

Preparation of 9-methyl-3-[(2-methyl-l-H-imidazol-l-yl)methyl]-l,2,3,9-tetrahydro-4H-carbazol-4-one hydrochloride dihydrate The process above described is followed, except that after cooling down the reaction mixture to room temperature after boiling, 20 ml of 37% aqueous hydrochloric acid are added thereto. Then, the precipitate is filtered off, washed with isopropanol and dried to obtain 2.40 g (65.6%) of the title salt, m.p. 178°-180°C. The active agent content of the product was found to be 100.3% based on potentiometric titration with sodium hydroxide solution. The theoretical water content is 9.85% (calculated for C18H19N30HCl2H20).The water content measured is 10.03%. 

Figure 4 Typical potentiometric titration curves for the precipitation of Ni(N03)2 (1), A1(N0 3) 3 (2), and a mixture of Ni(N03) 2 and A1(N03)3(3) using Na2C03 as precipitant. The concentrations used are typical of those used in catalyst preparation...

The pKa values of perhydropyridof 1,2-a]pyrazin-l -one, its 2-methyl derivative and their N-5 oxides were determined by potentiometric titration in a 4 1 mixture of 2-methoxyethanol and H20 (81BAP423).The partition coefficients of 3-substituted 2,3,4,4a,5,6-hexahydro-l//-pyrazino[l,2-a]-quinolines have been determined in water-l-octanol [80IJC(B)879],... 

Potentiometric titration of free 11 in aqueous solution indicated no tendency for deprotonation of the active methylene group below pH 11. In the presence of Zn(II), however, a similar titration indicated a deprotonation corresponding to a piiQ of 8.41. With the assistance of spectroscopic data, this deprotonation was unambiguously assigned to the formation of a 3 1 equilibrium mixture of [Zn(ll)(OH)]+ and the enolate complex [Zn(12)]+. 

The problem of the detection of the various equivalence-points in a mixture of acids of different concentrations or in a solution of a polybasic acid is essentially the same as that already discussed on page 406 in connection with potentiometric titration, and need not be treated further here. Where the conditions are such that the determination of an accurate end-point appears feasible, the appropriate indicator is the one whose pfcin value lies close to the pH at the required equivalence-point. 

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