Sampling of gases

The atmosphere itself is difficult to study, largely because it is not uniform in composition, temperature, or density (Table 4.1). One reason for this nonuniformity is the effect of solar radiation, which causes different chemical reactions at different altitudes (Box 4.1). The density of air also varies with altitude, partly because the temperature varies, but also as a result of the compressibility of air, its ability to be squashed into a smaller volume. The weight of air above compresses the air at sea level, causing it to be denser than the air at higher altitudes. The air outside an airplane cruising at 10 km is only 25% as dense as air at sea level. To simplify their task, scientists initially study samples of gases that are uniform in composition and density and only after uniform gases are understood do they turn their attention to more complex systems like the atmosphere. 

Gas Sampling The sampling of gases containing mists and sprays may be necessary to obtain data for collection-device design, in which case particle-size distribution, total mass loading, and gas volume,... 

Consider the following samples of gases at the same temperature. 

Note Some samples of gases may have equal values for these attributes. Assume the larger containers have a volume twice the volume of the smaller containers and assume the mass of an argon atom is twice the mass of a neon atom. 

The composition of fumes produced by detonation of explosives used in Poland Barbaryt A and Metanit D2 (Vol. Ill, pp. 478-479) was examined by Cybulska and Sobala (14). The fumes were analysed after the detonation in both laboratory conditions and in shot-hole underground. Samples of gases... 

When the volume of a gas is plotted against its pressure at constant temperature, the resulting curve is one branch of a hyperbola. Figure 12-4b is a graphic illustration of this inverse relationship. When volume is plotted versus the reciprocal of the pressure, /P, a straight line results (Figure 12-4c). In 1662, Boyle summarized the results of his experiments on various samples of gases in an alternative statement of Boyle s Law ... 

Up to this point, nearly all discussions and problems dealt with pure samples of gases, not mixtures of gases. But, one gas law specifically addresses mixtures this law was put forth by John Dalton in 1801 during his studies of the composition of the atmosphere. See Chapter 3 for more information on John Dalton s work. 

Using the ideal gas law, we can prove that equal volumes of two separate samples of gases, both at the same temperature and pressure, will have equal numbers of moles ... 

Environmental samples of gases and vapours arise from three main sources ... 

Rossner, A., Farant, J. P., Simon, P., and Wick, D. P., Development of a flow controller for long-term sampling of gases and vapors using evacuated canisters. Environ. Set Technol, 36,4912-4920, 2002. 

We often collect small samples of gases in the laboratory by bubbling the gas into a bottle or flask containing water. Explain why the gas becomes saturated with water vapor and how we must take the presence of water vapor into account when calculating the properties of the gas sample. 

Figures 13.7 and 13.8 show volume/temperature data for several samples of gases. Why do all the lines seem to extrapolate to the same point at -273 "C Explain. 

Uwer ExplosiM Uvt (LEL) eters—also called combustible gas meters, are probably the most common direct reading instruments. In a broad sense, the LEL instruments are based on the heat released by the sample of gases when they are burned under controlled environment Most instruments show the reading as the percent of the lower explosion limit (% LEL). LEI, meters usually also contain an oxygen sensor and are commonly called LEL/ O2 metms. There are several different designs but one of the most common is based on the heat of combustion of the burned hydrocarbon. 

Fig.l Glass containers for taking samples of gases a, expendable sampling ampoule (1), rubber stopper b, vacuum bottle. 

Samples of gases and volatile liquids can be introduced directly into the ionization chamber. Because the interior of a mass spectrometer is kept at a high vacuum, volatile liquids and even some solids are vaporized. For less volatile liquids and solids, the sample may be placed on the tip of a heated probe that is then inserted directly into the ionization chamber. Another extremely useful method for introducing a sample into the ionization chamber is to link a gas chromatograph (GC) or liquid chromatograph (LC) directly to the mass spectrometer. These machines can separate complex mixtures of molecules into pure firactions. Each firaction eluted firom the chromatograph enters directly into the ionization chamber of the mass spectrometer, enabling mass determination of the individual components. 

Few applications based on flow analysis can be found for the automated and direct determination of gaseous sulfur dioxide [8,9] or hydrogen sulfide [10] in atmospheric samples. This is mainly due to the difficulty encountered in the online sampling of gases, which has been partially overcome with the use of chromatomembrane cells or tubular and planar permeation denuders and diffusion cells for the collection of the analyte from air into an absorbing solution and its introduction into the flow manifold, followed by conductivity, potentiometric, piezoelectric, or spectrophotometric detection. 

Do all the molecules in a 1-mole sample of CILfg) have the same kinetic energy at 273 K Do all molecules in a 1-mole sample of N2(g) have the same velocity at 546 K Explain. Consider the following samples of gases at the same temperature. 

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