Mixing indexes

Mixed indicators give sharp color changes and are especially useful in titrating to a given titration exponent (p7). 

Methyl green, hexamethylpararosaniline hydroxymethylate (component of mixed indicator) dissolve 0.1 g in 100 mL alcohol when used with equal parts of hexamethoxytriphenyl carbinol gives color change from violet to green at a titration exponent (pi) of 4.0. 

Properties of Selected Indicators, Mixed Indicators, and Screened Indicators for Acid-Base Titrations... 

Mixed Indicator Acid Color Base Color pH Range... 

For the primary stage (phosphoric) V) acid as a monoprotic acid), methyl orange, bromocresol green, or Congo red may be used as indicators. The secondary stage of phosphoric) V) acid is very weak (see acid Ka = 1 x 10 7 in Fig. 10.4) and the only suitable simple indicator is thymolphthalein (see Section 10.14) with phenolphthalein the error may be several per cent. A mixed indicator composed of phenolphthalein (3 parts) and 1-naphtholphthalein (1 part) is very satisfactory for the determination of the end point of phosphoric(V) acid as a diprotic acid (see Section 10.9). The experimental neutralisation curve of 50 mL of 0.1M phosphoric(V) acid with 0.1M potassium hydroxide, determined by potentiometric titration, is shown in Fig. 10.6. 

The equivalence point for the primary stage of ionisation of carbonic acid is at pH = ( pK + pK2) = 8.3, and we have seen (Section 10.14) that thymol blue and, less satisfactorily, phenolphthalein, or a mixed indicator (Section 10.9) may be employed to detect the end point. 

It is sometimes possible to employ a mixed indicator (see Section 10.9) which exhibits a colour change over a very limited pH range, for example, neutral red-methylene blue for dilute ammonia solution and acetic (ethanoic) acid. 

The mixed indicator, bromocresol green-dimethyl yellow, may be used with advantage. The indicator consists of 4 parts of a 0.2 per cent ethanolic solution of bromocresol green and 1 part of a 0.2 per cent ethanolic solution of dimethyl yellow about 8 drops are used for 100 mL of solution. The colour change is from blue to greenish yellow at pH = 4.0 — 4.1 the colour is yellow at pH = 3.9. 

Procedure. Weigh an empty stoppered weighing bottle, add about 2 g of syrupy phosphoric(V) acid and re-weigh. Transfer the acid quantitatively to a 250 mL graduated flask, and then proceed as detailed for sulphuric acid, but using the phenolphthalein-1-naphtholphthalein mixed indicator. 

Procedure B. The experimental details for the preparation of the initial solution are similar to those given under Procedure A. Titrate 25 or 50 mL of the cold solution with standard 0.1M hydrochloric acid and methyl orange, methyl orange-indigo carmine, or bromophenol blue as indicator. Titrate another 25 or 50 mL of the cold solution, diluted with an equal volume of water, slowly with the standard acid using phenolphthalein or, better, the thymol-blue cresol red mixed indicator in the latter case, the colour at the end point is rose. Calculate the result as described in the Discussion above. 

In the second procedure a portion of the cold solution is slowly titrated with standard 0.1M hydrochloric acid, using phenolphthalein, or better, the thymol blue-cresol red mixed indicator. This (say, YmL) corresponds to half the carbonate (compare Section 10.32) ... 

A sharper colour change is obtained with the mixed indicator methyl red-bromocresol green (prepared from 1 part of 0.2 per cent methyl red in ethanol and 3 parts of 0.1 per cent bromocresol green in ethanol). 

Mixed indicator solution. Mix two volumes of 0.1 per cent phenolphthalein solution and three volumes of 0.1 per cent thymol blue solution (both in ethanol). 

Sodium hydroxide. Prepare a solution of approximately 0.5M sodium hydroxide in methylcellosolve. This should be standardised by titration with potassium hydrogenphthalate using the mixed indicator given below. 

Microphotometer 768 Microwave oven 97 Migration current 592, 596 Mixed indicators 267, (T) 268 Mobile phase 13, 217, 218, 222 Mobilities, ionic (T) 520 Modified voltammetric procedures 611 Modulation 791... 

Recently, several modifications of the two-phase titration and their precisions have been compared. The two-phase titration with the above-mentioned mixed indicator system, dimidium bromide/disulfine blue, is standardized in DGF (Deutsche Gesellschaft fur Fettforschung) and DIN methods, and is less time consuming and simpler than the standard gravimetric and extraction methods [18]. 

Initial surfactant concentration was 0.50% wt in pH 8.5 solution. 50 g of test solution was placed over 100.0 g crushed Berea sandstone. The sample bottle was sealed and shaken continuously for 24 h at 75°C. The mixed indicator titration technique was used to determine active surfactant concentration before and after exposure of the test solution to crushed Berea sandstone. AS HAS, alkene.hydroxyalkanemonosulfonate ratio. D.I. water, deionized water. ND, not determined. 

Gravimetric and volumetric methods are practicable for the quantitative determination of the a-sulfo fatty acid esters. Using gravimetric methods the surfactant is precipitated with p-toluidine or barium chloride [105]. The volumetric determination method is two-phase titration. In this technique different titrants and indicators are used. For the analysis of a-sulfo fatty acid esters the quaternary ammonium surfactant hyamine 1622 (p,f-octylphenoxyethyldimethyl-ammonium chloride) is used as the titrant [106]. The indicator depends on the pH value of the titration solution. Titration with a phenol red indicator is carried out at a pH of 9, methylene blue is used in acid medium [106], and a mixed indicator of a cationic (dimidium bromide) and an anionic (disulfine blue VN150) dye can be used in an acid and basic medium [105]. 

The Laue data (Table I) contain first-order reflections only from planes with all indices odd. This fact, together with the absence of reflections with mixed indices on oscillation photographs, shows the lattice to be face-centered. Of the two face-centered space groups isomorphous with point group Td, Td and Td, the latter requires that no odd-order reflections occur from planes (khl) with h — lc. The numerous observed... 

BASIS OF MANUAL PHOTOMETRIC TITRATION. The determination of anionic surfactants by a photometric titration employs a cationic indicator to form a coloured complex with the surfactant which is insoluble in water but readily soluble in chlorinated solvents (1 ). The end point of the titration occurs when there is a loss of colour from the organic phase. A considerable improvement in this technique is achieved by the use of a mixture of anionic and cationic dyes (4 ), for example disulphine blue and dimidium bromide (Herring s indicator (3)). The sequence of colour changes which occurs during the two phase titration of an anionic surfactant (AS) with a cationic titrant (CT) using a mixed indicator consisting of an anionic indicator (AD) and cationic indicator (CD) is summarised in Scheme 1 ... 

Size polymers on polyester can be determined by staining tests with Cl Basic Red 22, Cl Reactive Red 12, iodine/potassium iodide solution, or a mixed indicator. The extraction of size components and their determination in solution using a variety of reagents to give a characteristic coloration or a coloured precipitate has been described. Methods using fluorescence spectroscopy with a fluorescent cationic dye (e.g. Pinacryptol Yellow or Cl Basic Orange 14) were also described. 

Note that the calculated values are likely to be maximum values since for the 3n case one is not dealing with pure configurations, and in all cases %, Fe2+ may well be less than 400 cm-1 because of the extensive metal-ligand mixing indicated by the small (3 values. 

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