For acid-base titrations

Titrimetric (Volumetric) Factors for Acid-Base Titrations... 

Titrimetric (volumetric) factors for acids and bases are given in Table 11.28. Suitable indicators for acid-base titrations may be found in Tables 8.23 and 8.24. 

The utility of acid-base titrimetry improved when NaOH was first introduced as a strong base titrant in 1846. In addition, progress in synthesizing organic dyes led to the development of many new indicators. Phenolphthalein was first synthesized by Bayer in 1871 and used as a visual indicator for acid-base titrations in 1877. Other indicators, such as methyl orange, soon followed. Despite the increasing availability of indicators, the absence of a theory of acid-base reactivity made selecting a proper indicator difficult. 

The first two sensors were discussed in Section 9B.3 for acid-base titrations and are not considered further in this section. 

Ramsing and colleagues developed an FfA method for acid-base titrations using a carrier stream mixture of 2.0 X f0 M NaOH and the acid-base indicator bromthymol blue. Standard solutions of HCl were injected, and the following values of Af were measured from the resulting fiagrams. 

Table 5.1 A range of visual indicators for acid-base titrations...

M. C. Moreno, M. Jimenez, C. P. Conde, and C. Camara, Analytical performance of an optical pH sensor for acid-base titration, Anal ChimActa 230, 35-4) (1990). 

Acid-base, redox, precipitation and chelometric titrations are usually dealt with in textbooks on analytical chemistry. The titration curves in these titrations can be obtained potentiometrically by use of appropriate indicator electrodes, i.e. a pH-glass electrode or pH-ISFET for acid-base titrations, a platinum electrode for redox titrations, a silver electrode or ISEs for precipitation titrations, and ISEs for... 

We now turn our attention to details of precipitation titrations as an illustration of principles that underlie all titrations. We first study how concentrations of analyte and titrant vary during a titration and then derive equations that can be used to predict titration curves. One reason to calculate titration curves is to understand the chemistry that occurs during titrations. A second reason is to learn how experimental control can be exerted to influence the quality of an analytical titration. For example, certain titrations conducted at the wrong pH could give no discernible end point. In precipitation titrations, the concentrations of analyte and titrant and the size of Ksp influence the sharpness of the end point. For acid-base titrations (Chapter 11) and oxidation-reduction titrations (Chapter 16). the theoretical titration curve enables us to choose an appropriate indicator. 

Constant-boiling aqueous HCI can be used as a primary standard for acid-base titrations. When 20 wt% HQ (FM 36.461) is distilled, the composition of the distillate varies in a regular manner with the barometric pressure ... 

A more accurate way to use potentiometric data is to prepare a Gran plot6-7 as we did for acid-base titrations in Section 11-5. The Gran plot uses data from well before the equivalence poinl (Ve) to locate Ve. Potentiometric data taken close to Ve are the least accurate because electrodes are slow to equilibrate with species in solution when one member of a redox couple is nearly used up. 

Earlier, the work of Zetlmeisl and Laurence [22] was described. With their instrument, the current decayed exponentially during the titration. Control of the current via an algorithm can be done with the computer. An example of this is found in the work of Earle and Fletcher [64]. Their titrator was based on the Intel 8008, an early 8-bit microprocessor. For acid-base titrations, the applied current was reduced linearly with the difference in pH, ApH, between the measured value and the endpoint pH. An algorithm compared ApH with a set of rate functions specified in units of mA/pH. The magnitude of the current was then computed by multiplying ApH by the rate function. This process was repeated every 65.536 ms. The coulombs passed were computed for each of these time intervals and summed until the endpoint was reached. The result was then... 

Flair, M. and W. N. Setzer (1990) An olfactory indicator for acid-base titrations. Journal of Chemical Education 67(9), 795-796. 

For acid-base titrations, organic compounds that exhibit different colors in solutions of different acidities used to determine the point at which reaction between two solutes is complete. 

As it was for acid-base titrations, the concept of relative precision (Section 3-7) is useful for comparing the steepness of titration curves in the immediate vicinity of the end point. For the formation of a precipitate of symmetrical charge type (m = n), with activity coefficients assumed to be unity. 

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