Gaseous substances sampling

Contrast this availability in the inorganic realm with the substances that are readily available from organic nature. How could chemists extract pure substances from samples of plant tissue or flesh If plant or animal matter is subjected to distillation, then, typically, a black residue remains in the distillation vessel, and liquid and gaseous substances are driven off. The distillation of different plant substances produces substances that are qualitatively similar, so... 

In this category are Included all separation techniques In which the desired nuclides are separated as gaseous substances. If the nuclide to be separated Is a gaseous element to begin with or can be transformed easily at room temperature or at a somewhat elevated temperature Into a readlly-volatlle compound. It can be separated very easily and rapidly from the sample and then can be collected either by cooling or by absorption In a suitable solution. The ease or speed of such a separation method seems to be dependent upon the boiling point of the substance to be separated, as well as on characteristics of the matrix.material. 

The ideal gas law may be used to determine the molar mass of a gaseous substance. To determine a molar mass, we need the mass of a given sample and also the number of moles in that sample. The ideal gas law can be used to determine the number of moles. 

The Calculation of the Density of a Gas or the Weight of a Sample of Gas from Its Molecular Formula. If the molecidar formula of a gaseous substance is known, an approvimate value of its density can be calculated. This calculation can also be carried out for a mixture of known composition of gases of knotvn molecular formulas. The method to be used is illustrated in the following example ... 

An important result from aerosol chamber studies was the discovery of the indirect photochemical process. Thus, Bricard et al. (1968) found that intense aerosol particle production can be observed in the chamber in the dark if ambient filtered air is sampled from a sunlit atmosphere. It is speculated that in the atmosphere some gaseous substance is excited by sunlight and is not collected by the filter used to obtain air which is free of aerosol particles. In the chamber these photochemically excited molecules initiate secondary thermal reactions leading to the formation of some supersaturated vapour (e.g. H,S04) which subsequently condenses (see also Subsection 3.6.3). 

In a typical experiment, a bulb of known volume is filled with the gaseous substance under study. The temperature and pressure of the gas sample are recorded, and the total mass of the bulb plus gas sample is determined (Figure 5.11). The bulb is then evacuated (emptied) and weighed again. The difference in mass is the mass of the gas. The density of the gas is equal to its mass divided by the volume of the bulb. Once we know the density of a gas, we can calculate the molar mass of the substance using Equation (5.9). Example 5.10 shows this calculation. 

Thus far we have concentrated on the behavior of pure gaseous substances, but experimental studies very often involve mixtures of gases. For example, for a study of air pollution, we may be interested in the pressure-volume-temperature relationship of a sample of air, which contains several gases. In this case, and all cases involving mixtures of gases, the total gas pressure is related to partial pressures, that is, the pressures of individual gas components in the mixture. In 1801 Dalton formulated a law, now known as Dalton s law of partial pressures, which states that the total pressure of a mixture of gases is just the sum of the pressures that each gas would exert if it were present alone. 

In a sample of a gaseous substance, more than 99% of the overall volume of the sample is empty space. How is this fact reflected in the properties of a gaseous substance, compared with the properties of a liquid or solid substance ... 

Keep in mind that, as long as temperature remains constant, pressure-volume changes do not change the value of K. Rather, these changes alter the partial pressures of the gaseous substances. In Sample Exercise 15.8, we calculated Kp = 2.79 X 10 for... 

The substance mixture in question, which causes the odor, undergoes an overall investigation by means of a sensor array. In doing so, the device makes use of the semi-conductive properties of various metal oxides, which are on the surface of 12 sensors which react to the gaseous substances which come in contact with them. The response also depends on the temperature, humidity and flow rate of the gas. Each sensor issues its own reply signal as soon as the sample of air touches its surface. 

In a typical experiment, a bulb of known volume is filled with the gaseous substance under study. The temperature and pressure of the gas sample are recorded, and the total... 

So far our discussion of the physical properties of gases has focused on the behavior of pure gaseous substances, even though the gas laws were all developed based on observations of samples of air, which is a mixture of gases. In this section, we will consider gas mixtures and their physical behavior. We will restrict our discussion in this section to gases that do not react with one another that is, ideal gases. 

Figure 1.2 depicts a typical macroscopic system, a sample of a single gaseous substance that is contained in a cylinder with a movable piston. The cylinder is immersed in a constant-temperature bath that can regulate the temperature of the system. The volume of the system can be adjusted by moving the piston. There is a valve between the cylinder and a hose that leads to the atmosphere or to a tank of gas. When the valve is elosed so that no matter can pass into or out of the system, the system is called a closed system. When the valve is open so that matter can be added to or removed from the system, it is called an open system. If the system were insulated from the rest of the universe so that no heat could pass into or out of the system, it would be called an adiabatic system and any process that it undergoes would be called an adiabatic... 

Many common laboratory preparations of gaseous substances involve collecting the gas produced by displacement of water from a receiving container (see Figure 12.12). What happens to a gas sample when it is collected by displacement of water How is Dalton s law of partial pressures used in determining the partial pressure of the prepared gas in such an experiment ... 

Thin films of metals, alloys and compounds of a few micrometres diickness, which play an important part in microelectronics, can be prepared by die condensation of atomic species on an inert substrate from a gaseous phase. The source of die atoms is, in die simplest circumstances, a sample of die collision-free evaporated beam originating from an elemental substance, or a number of elementary substances, which is formed in vacuum. The condensing surface is selected and held at a pre-determined temperature, so as to affect die crystallographic form of die condensate. If diis surface is at room teiiiperamre, a polycrystalline film is usually formed. As die temperature of die surface is increased die deposit crystal size increases, and can be made practically monocrystalline at elevated temperatures. The degree of crystallinity which has been achieved can be determined by electron diffraction, while odier properties such as surface morphology and dislocation sttiicmre can be established by electron microscopy. 

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