Ebulliometer

C, ebulliometer and inclined piston gauge, measured temp range 268-490 K. Chirico et al. 1989)... 

Making careful use of an ebulliometer we can make an accurate measurement of Molecular weights of... 

One of the critical issues in vapor pressure methods is the choice of the procedure to calculate the vaporization enthalpy. For instance, consider the vapor pressures of ethanol at several temperatures in the range 309-343 K, obtained with a differential ebulliometer [40]. The simplest way of deriving an enthalpy of vaporization from the curve shown in figure 2.4 is by fitting those data with the integrated form of the Clausius-Clapeyron equation [1] ... 

Alcohol by ebulliometer Alcohol by hydrometer Alcohol by pycnometer Brix by hydrometer Brix by refractometer Total acidity by titration Volatile acidity by titration... 

This paper describes an ebulliometric system for routine and special determinations of molecular weights. The system uses a simple ebulliometer, an immersion heater, and a Cottrell-type pump. Temperature sensing is by differential thermopile. Precision varies from about 1 to 6%, and values compare well with those from other laboratories and those from other methods. Values as high as 170,000 have been successfully measured. Some problems encountered in using the ebulliometric method are selection and effect of reference temperature, limitations of the vapor lift pump and a possible substitute for it, measurement of equilibrium concentrations within the operating ebulliometer, and the experimentally determined ebulliometric constant and some factors which influence its value. 

EBULLISM. The formation of buhbles. with particular reference to water vapor bubbles in biological fluids caused by reduced ambient pressure the boiling of body fluids. Sec also Ebulliometer. 

Lenchitz, C., Vebcky, R.W. (1970) Vapor pressure and heat of sublimation of three nitrotoluenes. J. Chem. Eng. Data 15(3), 401-403. Lencka, M. (1990) Measurements of vapour pressures of pyridine, 2-methyl pyridine, 2,4-dimethylpyridine, 2,6-dimethylpyridine, and 2,4,6-trimethylpyridine from 0.1 kPa to atmospheric pressure using a modified -wietos-awski ebulliometer. J. Chem. Thermodyn. 22, 473-480. 

The number average molecular weight of the degraded polymers was measured on an ebulliometer, using toluene as a solvent and a tristearin standard. Intrinsic viscosities of the polymers were determined using a Desreux dilution viscometer. 

In this method, the boiling points of solutions of known concentration are compared to that of the solvent, at the same temperature. Tlie apparatus tends to be complicated, and errors are possible from ambient pressure changes and the tendency of polymer solutions to foam. Present-day commercial ebulliometers are not designed for molecular weight measurements in the range of major interest with synthetic polymers. The method is therefore only used in laboratories which have designed and built their own equipment. 

Another conceptually simple method is ebulliometry, where the liquid is boiled under total reflux at a fixed pressure and the boiling temperature is measured. Because of the difficulty of accurately measuring the temperature of a boiling liquid, ebulliometers typically measure the temperature of the condensing vapor. An advantage to ebulliometry is that volatile impurities are purged as the system approaches steady state, so the need for degassing is reduced. The attainable... 

Crude measurements are easy to perform with this technique. With careful attention to details, however it is possible to make the most accurate measurements over the range of 2000 to 200,000 Pa using ebulliometers. With high quality samples, boiling point accuracy of 0.01 °C or better is possible. 

A variation on this technique is twin ebulliometers. In this technique, two matched ebulliometers are connected to the same external pressure at the top of the condenser. A standard substance with accurately known vapor pressure is placed in one ebulliometer and the test sample in the other. When steady boiling is attained in both sides, they are at the same pressure. Pressure is not measured directly rather the two boiling temperatures are measured. Pressure is established by converting the boihng point of the standard to pressure using a previously determined relationship. For organic liquids, water, benzene, or decane are often used as standards. 

In a similar fashion, for the constant-pressure ebulliometer, we have (Problem 10.2-13)... 

As pointed out above, dynamic vapor-hquid equilibrium measurement mediods are not very suitable for concentrated polymer solutions, especially due to their heavy foaming behavior. For dilute polymer solutions, however, diere is continuing apphcation of ebulhomelry as an absolute method for the direct determination of die number-average molecular mass M . Dedicated differential ebulliometers allow the determination of values up to an order of 100,000 g/mol. Ebulliometry as a mediod for molar mass determination was recently reviewed by Cooper, Glover, and Mays and Hadjichristidis. ... 

Figure 1.65 illustrates a differential ebulliometer for the measurement of boiling point elevations. This ebulliometer gives the precision which is required for... 

Experimental determination of VLE data depends very much on the choice of still. The traditional type of a circulation still is unsatisfactory for a reacting system since the compositions of the phases are constantly changing. This necessitates the use of a flow still. Pilavakis (28) used for this purpose a suitably modified version of the Cathala ebulliometer (42) which was first successfully tested on a number of well known binary mixtures. 

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