Thermometric titrimetry

Thermometric titration depends on measuring the heat generated during a chemical reaction therefore it is another calorimetric technique. Usually the reactions take place at room temperature under conditions such that no heat enters or leaves the titration cell except that brought in by introduction of the titrant. In this procedure a titrant of known concentration is added to a known volume of sample. The titration reaction follows the generalized chemical equation 

For any particular reaction, a mole of A titrated with a mole of B will generate a fixed quantity of heat, which is the heat of reaction. If there is half a mole of A present, half as much heat is generated, even if there is an excess of B. Heat is generated only while A and B react with each other an excess of either one does not cause generation of heat. The reaction is usually set up in an insulated beaker, a Dewar flask, or a Christiansen adiabatic cell. This ensures a minimum of heat loss from the system during titration. 

In practice, the temperature of the system is measured as the titrant is added to the sample. A thermometric titration plot generally has AT on the y-axis and volume of titrant on the x-axis. A typical plot for an exothermic reaction is shown in Fig. 16.31. We will 

For simple titrations the equipment necessary is not particularly sophisticated a thermometer, a buret, and an insulated beaker (or even two Styrofoam cups, one sitting in the other) will do. However, if one wants to measure specific heats or the heat of reaction, better control is required. Modern automated thermometric titrators consist of a constant delivery pump for the titrant, a temperature control system for the titrant, an insulated cell, cahbration circuitry, electronic temperature sensing, and a data processing system. Most modem instraments are totally computerized, so different methods can be programmed and mn unattended. 

The titrant is delivered with a motorized syringe pump. This permits the volume of titrant to be calculated from the rate of delivery. These pumps are able to deliver rates of flow down to microhters per minute with high precision. The temperature control system, usually a thermostatted bath for the titrant and a heater for the sample cell, is used to bring the titrant and the sample to exactly the same temperature. This is required for high precision measurements of heat capacity and enthalpy. Modem thermostats can maintain the temperature to within 0.001°C. 

For simple titrations, the equipment necessary is not particularly sophisticated a thermometer, a burette, and an insulated beaker (or even two Styrofoam cups, one sitting in the other) will do. However, if one wants to measure specific heats or the heat of reaction, better control is required. 

The TT plot tor HCI (a strong acid) with NaOH would look virtually identical to the TT plot tor boric acid (a very weak acid) with NaOH because the A/f of reaction is almost the same for both acids. 

Modem automated thermometric titrators consist of a constant delivery pump for the titrant, a temperature control system for the titrant, an insulated cell, calibration circuitry, electronic temperature sensing, and a data processing system. Most modem instruments are totally computerized, so different methods can be programmed and run unattended. 

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Eatough, D.J. Christensen, J.J. Izatt, R.M. "Experiments in Thermometric Titrimetry and Titration Calorimetry" Brigham Young Univ. Press Provo, UT, 1974. 

D. J. Eatough, J. J. Christensen, R. M. Izatt. Experiments in Thermometric Titrimetry and Titration Calorimetry. Brigham Young University Press Provo, 1974. 

Conventional thermometric titrimetry was used to determine base and acid content in light and heavy petroleum derivatives, including lubricating oils (Quilty, 1967), crude oils (Borrull et al., 1986a) and petroleum distillates (Borrull et al., 1986b Greenhow andNadjafi, 1979). Studies show that the acids in the oils not determined by the thermometric method are weaker than pKa(H20) = 10. 

L. s. BARK and s. m. bark Thermometric Titrimetry, chap. 7, Pergamon, London, 1969. 

The committee did not wish to pronounce on nomenclature in borderline techniques (such as thermometric titrimetry or calorimetry) which are. to its knowledge, being considered by other bodies. Consideration of techniques not yet extensively employed has been deferred. 

Direct injection enthalpimetry (DIE) is similar in many respects to thermometric titrimetry. One essential difference is that an excess of titrant is added very rapidly to the sample and the reactants mixed vigorously. The temperature is then measured against time following the injection of the titrant, as shown in Fig. 16.32. We may suppose that the following exothermic reaction takes place ... 

The equipment used for DIE is identical to that for thermometric titrimetry. The titrant must be at the same temperature as the sample at the start of the experiment, and the syringe is emptied rapidly into the cell to deliver the titrant instantaneously . 

Tyrell, H.V. Beezer, A.E. Thermometric Titrimetry Chapman and Hall London, 1968. 

H.J.V. Tyrrell and A.E. Beezer, Thermometric Titrimetry, Chapman and Hall, London, 1968. 

L. S. Bark and S. M. Bark, Thermometric Titrimetry, Pergamon Press, London, 1969. 

Titrimetry may also be classified by the nature of the endpoint measurement. The use of electrical measurements gives rise to potentiometric, ampero-metric, and coulometric titrations. Measurement of heat changes is used in thermometric titrimetry, and of absorbance in photometric and turbidimetric titrations. Radiometric titrations measure changes in radioactivity during the titration. All of these techniques are dealt with in other articles in this Encyclopedia. This article discusses only those titrations that use visual indicators. 

Formed by autoxidation of cumene. Strong oxidizing agent. Used in phenol manuf. Polymerization initiator. End point indicator in the titration of bases by catalytic thermometric titrimetry. Liq. Bp 153°. 1.5242. 

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