Acid mixed indicator

This method is based on the titration of basic ammonia with standard sulfuric acid using methyl red-methylene blue indicator to pale lavender end point. Distill 100 mL sample into 50 mL boric acid mixed indicator solution. Titrate ammonia in this distillate solution with standard H2S04 (0.02 N) until the color turns to pale lavender. Perform a blank titration using distillate obtained from reagent grade water under similar conditions. Calculate the concentration of NH3-N in the sample as follows ... 

Indicator weigh 0.5 g disulphine blue VN and 0.5 g dimidium bromide in two 50 ml beakers. Add 25 ml hot 10% aqueous ethanol to each and stir until dissolved. Transfer both solutions to a 250 ml volumetric flask, dilute to volume and mix. This is the stock solution. Place 200 ml water and 20 ml stock solution in a 500 ml volumetric flask, add 20 ml 2.5 M sulphuric acid, dilute to volume and mix. This is the acid mixed indicator. 

Transfer 25 ml by pipette to a titration vessel. This may be a 100 ml stoppered measuring cylinder or bottle, but it is much better to use the mechanical apparatus described in ISO 2271 1989 (E), which is shown in Figure 3.2. Add 10 ml water, 15 ml chloroform and 10 ml acid mixed indicator. 

If necessary, confirm the completeness of the deionisation as follows. Dissolve the residue from step 8 in chloroform and dilute to volume in a volumetric flask. Test a portion of this solution for the presence of whatever ionic surfactant predominated in the sample, e.g. by adding water and acid mixed indicator and titrating with benzethonium chloride. If the nonionic matter is not completely free of ionic surfactants, repeat the analysis using twice as much resin. 

Add 10 ml water, 15 ml chloroform and 10 ml acid mixed indicator (disulphine blue VN and dimidium bromide). 

At step 3, replace the acid mixed indicator with 1.0 ml 0.04% bromophenol blue and 10 ml 0.1 M sodium hydroxide. 

Pipette a 20 mi portion into a titration vessel, add acid mixed indicator and chloroform and titrate with 0.004 M benzethonium chloride according to ISO 2271. 

Titrate with 0.004 M sodium dodecyl sulphate using acid mixed indicator (cf. ISO 2871-2). 

Titrate two 25 ml portions with 0.004 M benzethonium chloride, one portion using acid mixed indicator and the other using bromophenol blue in alkaline solution. 

Pipette 25 ml of this solution into a suitable titration vessel. Add 25 ml chloroform, 25 ml water and 10 ml acid mixed indicator and titrate with 0.004 M sodium dodecyl sulphate, shaking thoroughly after each addition. The chloroform is initially blue, becoming colourless or greyish at the end-point. A pink colour indicates that the end-point has been overshot. 

Acid mixed indicator solution To a 250-mL volumetric flask add 0.050 g dimidium bromide dissolved in 15 mL hot 10 90 EtOH/H20 and 0.050 g disulphine blue V which has been dissolved in 10 mL hot 10 90 EtOH/H20. Add about 100 mL water and 10 mL 2.5 M H2SO4, then dilute to volume with water. Store protected from light. 

An aqueous solution of the sample is prepared at about 0.001 M. Ten milliliters are added to a glass-stoppered conical flask, together with 10 mL acid mixed indicator solution, 0.235 mL concentrated H2SO4,15 mL CHCI3, and 5.0 mL 95% ethanol. Titrate with 0.001 M dodecanesulfonate solution, shaking vigorously after each addition of titrant. At the end point, the chloroform phase is light pink. 

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

Mixed Indicator Acid Color Base Color pH Range... 

When equal amounts of solutions of poly(ethylene oxide) and poly(acryhc acid) ate mixed, a precipitate, which appears to be an association product of the two polymers, forms immediately. This association reaction is influenced by hydrogen-ion concentration. Below ca pH 4, the complex precipitates from solution. Above ca pH 12, precipitation also occurs, but probably only poly(ethylene oxide) precipitates. If solution viscosity is used as an indication of the degree of association, it appears that association becomes mote pronounced as the pH is reduced toward a lower limit of about four. The highest yield of insoluble complex usually occurs at an equimolar ratio of ether and carboxyl groups. Studies of the poly(ethylene oxide)—poly(methacryhc acid) complexes indicate a stoichiometric ratio of three monomeric units of ethylene oxide for each methacrylic acid unit. 

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. 

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) ... 

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]. 

Thiolsulfonates have the structure shown in [58]. That they may be considered the mixed anhydride of a sulfenic and a sulfinic acid is indicated by one of the principal synthetic methods for their preparation, namely reaction (166) of a sulfinic acid with a sulfenyl chloride (Stirling, 1957). Once again, as we have... 

The acidity of various substances is determined with a pH meter or acid—base indicators. This may also be done by mixing or diluting solutions. (See the Equilibrium chapter.)... 

Procedure Transfer an accurately measured volume of about 30.0 ml of 0.1 N potassium bromate solution into a 250 ml iodine flask. Add to it 3.0 g potassium iodide, followed by 3.0 ml of potassium iodide, followed by 3.0 ml of hydrochloric acid. Mix the contents thoroughly and allow it to stand for 5 minutes with its stopper in position. Titrate the liberated iodine with previously standardized 0.1 N sodium thiosulphate, using 3.0 ml of freshly prepared starch solution as an indicator at the end-point. Carry out a blank run using the same quantities of the reagents and incorporate the necessary corrections, if any. Each ml of 0.1 N sodium thiosulphate is equivalent to 0.002784 g of KBr03. 

In an acid-base titration, you carefully measure the volumes of acid and base that react. Then, knowing the concentration of either the acid or the base, and the stoichiometric relationship between them, you calculate the concentration of the other reactant. The equivalence point in the titration occurs when just enough acid and base have been mixed for a complete reaction to occur, with no excess of either reactant. As you learned in Chapter 8, you can find the equivalence point from a graph that shows pH versus volume of one solution added to the other solution. To determine the equivalence point experimentally, you need to measure the pH. Because pH meters are expensive, and the glass electrodes are fragile, titrations are often performed using an acid-base indicator. 

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