Indicators for titration

Thymol blue is used extensively as an indicator for titrations of substances acting as acids in dimethylformamide solution. It is used as a 0.2 per cent w/v solution in methanol with a sharp colour change from yellow to blue at the end point. 

I mol of commercial grade sulfosalicylic acid is combined with 0.75 mol of reagent-grade KHC03, recrystallized several times from water, and dried at 110°C to produce the double salt with 3 K+ ions and one titratable H+.15 Phenolphthalein is used as the indicator for titration with NaOH. 

The parent compd in ale soln was found to be fairly good indicator for titration of acids but less precise in titrating alkalies Refs l)Be>I- not found 2)C.Musante,Gazz 76,297(1946) CA 41,7298(1947)... 

Table 5.21 Commonly used pH indicators for titrations in nonaqueous solvents...

The complexes are useful as indicators for titrating weak bases in nonaqueous solvents and also for oxidation-reduction and aromatic diazotization titrations.4 8... 

With use of these rules we can answer questions as to the hydrolysis of salts or the choice of indicators for titration without referring to tables of acid constants. 

An iron-selective electrode based on a glass Fe-1173 (Ge2sSbx2Seeo) has been reported to respond to xmcomplexed iron(ni) in sulfate solutions. It was used to evaluate formation constants of iron(III)-sulfate complexes and as an indicator for titrations of sulfate with barium. The mechanism of the sensing action is obscure. 

In calculating the amount of caustic required for caustic neutralization, the oil is titrated to a phenolphthalein end point. This titration endpoint includes not only the FFA, but also the oryzanol compounds. With the higher caustic addition, the ory-zanol is transferred to the soapstock away from the oil. The nutritional benefit of these compounds is lost. An alternative indicator for titration uses alkali blue (8). This indicator reflects the acidity contributed only by the free fatty acids. 

How would you choose an indicator for titrating a strong acid with a strong base ... 

Indicator for titrations. Phenolphthalein, methyl red, and o-cresolphthalein are dissolved in 90 per cent methanol. The useful concentration is 0.5 to 1.0 g per liter. 

The orange color of a dichromate solution is not intense enough for use in end point detection. Diphenylamine sulfonic acid (see Table 19-2) is an excellent indicator for titrations with this reagent, however. The oxidized form of the indicator is violet, and its reduced form is essentially colorless thus, the color change observed in a direct titration is from the green of chromium(III) to violet. 

FIGURE 17,14 Good and poor indicators for titration of a weak acid with a strong bass. 

Figure 17.12 Using color indicators for titration of a strong base with a strong acid. Both phenolphthalein and methyl red change color in the rapid-rise portion of the titration curve. 

Acid-base indicators for titrations in nonaqueous solvents are normally weak protolytes. For dissociation model I as given in Table 1, the acid-base equilibrium of a weak acid type of indicator in the pure solvent can be represented in water by the following reaction ... 

Litmus is included in the list to show how insensitive it is, relatively, when compared with the newer reagents. A change of three pH degrees is required to alter it from red to blue. Phenol red is a much sharper indicator for titrations to the end-point of absolute neutrality, pH 7 0. 

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