Volumetric technique

In pycnometry, the sample is weighted in a calibrated pycnometer before and after this is filled with a liquid of known density. The volume of the sample and thus its mass is determined. Powders may be used, and it is often advantageous to 

Other methods are obviously needed for liquids. In the simplest approach the thermal expansivity is derived by measurements of the density as a function of temperature. It is then necessary to correct for the thermal expansion of the solid body 

Several methods are also available for determination of the isothermal compressibility of materials. High pressures and temperatures can for example be obtained through the use of diamond anvil cells in combination with X-ray diffraction techniques [10]. kt is obtained by fitting the unit cell volumes measured as a function of pressure to an equation of state. Very high pressures in excess of 100 GPa can be obtained, but the disadvantage is that the compressed sample volume is small and that both temperature and pressure gradients may be present across the sample. 

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A volumetric technique is generally to be preferred especially when reasonable accuracy is required in the region of high relative pressure, as in... 

Besides shear-induced phase transitions, Uquid-gas equilibria in confined phases have been extensively studied in recent years, both experimentally [149-155] and theoretically [156-163]. For example, using a volumetric technique, Thommes et al. [149,150] have measured the excess coverage T of SF in controlled pore glasses (CPG) as a function of T along subcritical isochoric paths in bulk SF. The experimental apparatus, fully described in Ref. 149, consists of a reference cell filled with pure SF and a sorption cell containing the adsorbent in thermodynamic equilibrium with bulk SF gas at a given initial temperature T,- of the fluid in both cells. The pressure P in the reference cell and the pressure difference AP between sorption and reference cell are measured. The density of (pure) SF at T, is calculated from P via an equation of state. 

Fernandez and Sanchez [18] investigated the kinetics of hydrogen absorption and desorption by activated magnesium powder (several cycles of hydrogen absorp-tion/desorption at 375°C) using a volumetric technique. They pointed out that for-mation/decomposition of metal hydrides comprises a number of steps taking place in series transport to the surface, dissociation, H chemisorption, surface-... 

Presently, calorimetry linked to the volumetric technique is still the most commonly used method to study the gas-solid interactions [123], A complete description of the technique and valuable information provided is given in the different reviews by Cardona-Martinez and Dumesic [118], Auroux [145], Andersen and Kung [153] and Farneth and Gorte [154]. 

The BET surface areas and pore diameters were determined by nitrogen adsorption/ desorption isotherms at 77 K using a static volumetric technique (Quantachrome Autosorb 1). Before the physisorption measurements the samples were outgassed at 100° C for 15 hours under vacuum. 

In general, solid solutes should be weighed on weighing paper or plastic weighing boats, using an analytical or top-loading balance. Liquids are more conveniently dispensed by volumetric techniques however, this assumes that the density is known. If a small amount of a liquid is to be weighed, it should be added to a tared flask by means of a disposable Pasteur pipet with a latex bulb. The hazardous properties of all materials should be known before use and the proper safety precautions obeyed. 

Subsequent work on catalyst characterization via reduction studies has involved gravimetric or volumetric techniques. The gravimetric method measures weight loss (due to O loss), while the volumetric method measures amount of H2 consumed [and amount of water formed (O loss)]. In the latter case, the amount of H retained by the catalyst can also be determined (20). The gravimetric technique has also been applied to sulfided catalysts (27). From these measurements, the stoichiometric state of the catalyst can be determined. 

T. V. Chalikian, J. Volker, G. E. Plum, and K. J. Breslauer, A More Unified Picture for the Thermodynamics of Nucleic Acid Duplex Melting A Characterization by Calorimetric and Volumetric Techniques , Proc. Natl Acad. Sci. USA, 96, 7853-7858 (1999). 

The conventional approach is to equilibrate an excess amount of the pure chemical with an aqueous solution at controlled temperature and measure the concentration of the solution. Common analytical methods include gravimetric or volumetric techniques, spectroscopy, gas chromatography, and scintillation counting. Difficulties may be encountered with the presence of micro-particles of pure chemical phase which may give an apparently high solubility. 

The most common method used for the determination of surface area and pore size distribution is physical gas adsorption (also see 1.4.1). Nitrogen, krypton, and argon are some of the typically used adsorptives. The amount of gas adsorbed is generally determined by a volumetric technique. A gravimetric technique may be used if changes in the mass of the adsorbent itself need to be measured at the same time. The nature of the adsorption process and the shape of the equilibrium adsorption isotherm depend on the nature of the solid and its internal structure. The Brunauer-Emmett-Teller (BET) method is generally used for the analysis of the surface area based on monolayer coverage, and the Kelvin equation is used for calculation of pore size distribution. 

The above discussion in terms of the volumetric technique when applied to gravimetric measurements gives for the apparent change in weight... 

It is essential to take into account a number of potential sources of experimental error in the determination of an adsorption isotherm. In the application of a volumetric technique involving a dosing procedure it must be kept in mind that any errors in the measured doses of gas are cumulative and that the amount remaining unadsorbed in the dead space becomes increasingly important as the pressure increases. In particular, the accuracy of nitrogen adsorption measurements at temperatures of about 77 K will depend on the control of the following factors ... 

The chemical transformation of Ru-complexes in faujasite-type zeolites in the presence of water and of carbon monoxide-water mixtures is reviewed and further investigated by IR, UV-VIS spectroscopic and volumetric techniques. The catalytic activity of these materials in the watergasshift reaction was followed in a parallel way. The major observations could be rationalized in terms of a catalytic cycle involving Ru(I)bis and triscarbonyl intermediates stabilized in the supercages of the faujasite-type zeolite. The turnover frequency of this cycle is found to be determined by the nature, number and position of the charge compensating cations, as well as by the nature of the ligands present in the Ru-coordination sphere. 

At higher temperatures, the residual hydration water causes further hydrolysis and Ru-Red becomes a dominating species (Table 2). The color of the sample (wine-red) as well as the absorption in the UV-VIS region (7, 10) are typical. The volumetric techniques indicate that almost 80 % of the Ru contributes to this species. The continuing hydrolysis of the Ru(III)pentammine-hydroxy to the final Ru-Red complex may occur in a way similar to the aqueous solution phase chemistry, as proposed earlier (7) ... 

Precautions. In order to obtain successful results from this experiment, careful volumetric technique and judicious handling of reagents are required. The following points should be noted. 

Adsorption from the gas phase can be measured by either gravimetric or volumetric techniques. In the gravimetric method, the weight of adsorbed gas is measured by observing the stretching of a helical spring from which the adsorbent is himg (see Fig. 2).f Alternatively,... 

The textural properties of all calcined samples were determined by nitrogen isotherms at liquid N2 temperature, using a Micromeritics ASAP 2010 apparatus (static volumetric technique). Before determination of adsorption-desorption isotherms the samples ( 0.2 g) were outgassed for 16 h at 350 °C under vacuum. 

Chalikian TV, Volker J, Plum GE, Breslauer KJ. A more unified 36. picture for the thermodynamics of nucleic acid duplex melting a characterization by calorimetric and volumetric techniques. Proc. 

We used a typical GC setup and a mass spectroscopic detector. The only modification involves controlling column pressure between 20 - 1000 kPa. The following table lists the main features of the experimental system used. All previous attempts to use the GC technique for binary measurements were conducted at constant (atmospheric) pressure. The pure component isotherms are obtained form a conventional volumetric technique. 

The selectivity of 2 ( 2,1) at these conditions is given by Eq.(3). The quantity ni P) in the above equation is the pure component amount adsorbed for gas 1 at total column pressure P. Experimental measurements are required for 1 (obtained from the infinite dilution system) and data for pure component isotherm (obtained independently using a volumetric technique) to calculate selectivity (LHS of Eq.3). A similar equation can be written for the infinite dilution of gas 1. 

Figure 1.7 shows the physisorption isotherm, obtained using the non continuous volumetric technique, of a mesoporous alumina (type IV isotherm) and the results of analysis procedures (BET transform, /-curve, BJH porous distribution). This solid presents a specific surface area of approximately 200 m /g with the narrow pore size distribution at around 10 nm. The shape of the /-curve shows that it does not contain any micropores. 

Chemistry Video Consortium, Practical Laboratory Chemistry, Educational Media Film and Video Ltd, Harrow, Essex, UK - Volumetric techniques (using a balance, using a pipette, using a burette and making-up solutions). 

We now cite the types of experimental data in the literature, by which an analysis of surface adsorption effects is carried out. One common experiment involves measuring adsorption isotherms. By weighing or by volumetric techniques one determines as a function of equilibrium gas pressure the amount of gas held on a given surface at a specified temperature. Usually this quantity varies sigmoidally with rising pressure P, as sketched in Fig. 5.2.1 for a variety of temperatures 7). By standard methods that rely on the Brunauer, Emmett, Teller isotherm equa-tion one can determine the point on the isotherms at which monolayer coverage of the surface is complete it is usually is located fairly close to the knee of the isotherm. From the cross sectional area of the adsorbate molecules and from the amount needed for monolayer coverage one may then ascertain more or less quantitatively the surface area of the adsorbent. As-... 

Surface properties of all the samples were determined from physical adsorption measurements by volumetric techniques, using Nj at -196 °C and COj at 25 °C. The complementary use of these adsorbates allows characterisation of complex networks of pores of different sizes (5). A Micromeritics Gemini 2360 surftce area analyser was employed for Nj adsorption experiments, whereas adsorption measurements performed with CO2 were carried out in a Micromeritics Accusorb 2100E soiption instrument. All the samples were outgassed overnight at 120°C at a final pressure of 1.33 x lO Pa (10 mm Hg) prior to adsorption measurements. 

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