Concentration units used conversion between

No deaths or evidence of toxicity were attributable to diisopropyl methylphosphonate administered for 26 weeks in the drinking water of rats at concentrations of 0.6 ppb, 6.0 ppb, 10 ppm, and 1,000 ppm (6.6x 10"7, 6.6x 10"5, 0.011, and 1.1 mg/kg/day, respectively) (Army 1978). It should be noted that there is some confusion concerning the concentration units used in this study (EPA 1989). EPA (1989) states that conversions between ppm and mg/L were incorrectly calculated using the air conversion factor. 

The conversion between concentration units and the expression of the units themselves can be confusing. We will now review the typical concentration units used in various environmental media. Concentration in water is usually given as mass per unit volume or moles per unit volume. The conversion between them is a straightforward application of molecular weights. For example, we have 2.0 g/m of CO2 dissolved in water. The molecular weight of carbon dioxide is 44 g/mole. Then the concentration in moles/m is... 

All of the solution concentration units introduced in this chapter are direct proportionalities. Percentage concentration by mass is a direct proportionality between mass of solute and mass of solution molarity, between moles of solute and liters of solution molality, between moles of solute and kilograms of solvent and normality, between equivalents of solute and liters of solution. These proportional relationships allow you to think of solution concentration units as conversion factors between the two units in the fraction. Do you know mass of solution and need mass of solute Use percentage concentration. Do you know volume of solution and need moles of solute Use molarity. Thinking about solution concentration units in this way allows you to become more skilled at solving quantitative problems. 

Pourbaix has evaluated all possible equilibria between a metal M and HjO (see Table 1.7) and has consolidated the data into a single potential-pH diagram, which provides a pictorial summary of the anions and cations (nature and activity) and solid oxides (hydroxides, hydrated oxides and oxides) that are at equilibrium at any given pH and potential a similar approach has been adopted for certain M-H2O-X systems where A" is a non-metal, e.g. Cr, CN , CO, SOj , POj", etc. at a defined concentration. These diagrams give the activities of the metal cations and anions at any specified E and pH, and in order to define corrosion in terms of an equilibrium activity, Pourbaix has selected the arbitrary value of 10 ° g ion/1, i.e. corrosion of a metal is defined in terms of the pH and potential that give an equilibrium activity of metal cations or anions > 10 g ion/1 conversely, passivity and immunity are defined in terms of an equilibrium activity of < 10 g ion/1. (Note that g ion/1 is used here because this is the unit used by Pourbaix in the S.I, the relative activity is dimensionless.)... 

These results are in apparent contradiction to others obtained by the same authors [53]. In this earlier paper" they reported that at -78°, with the same range of [A1C13] [/-C4H8] ratios, and at conversions of less than 10 per cent, the DP decreased from 5.4 x 103 at 4.8 x 10"3 wt.% A1C13 on isobutene, to about 2.5 x 103 at concentrations greater than about 1.3 x 10"2 wt.% of A1C13. The authors do not comment on this apparent discrepancy between their two series of results, which is rendered even more obscure by the different, but equally clumsy, concentration units which are used in the two papers. The matter... 

The composition of a mixture need not be given in terms of the mole fractions of its components. Other scales of concentration are frequently used, in particular, when one of the components, say. A, can be designated as the solvent and the other (or others), B, (C,...) as the solute (or solutes). When the solute is an electrolyte capable of dissociation into ions (but not only for such cases), the molal scale is often employed. Here, the composition is stated in terms of the number of moles of the solute, m, per unit mass (1 kg) of the solvent. The symbol m is used to represent the molal scale (e.g., 5 m = 5 mol solute/1 kg solvent). The conversion between the molal and the rational scale (i.e., the mole fraction scale, which is related to ratios of numbers of moles [see Eq. (2.2)] proceeds according to Eqs. (2.32a) or (2.32b) (cf. Fig. 2.4) ... 

The reverse rate constants for the elementary reactions used in the present work were caJculated from the forward rate constants and the equilibrium constant by assuming microscopic reversibility. Standard states used in tabulations of thermodynamic data are invariably at 1 atm and the temperature of the system. Since concentration units were required for rate constant calculations, a conversion between Kp and Kc was necessary. Values of Kp were taken from the JANAF Thermochemical tables (1984). Kc was calculated from the expression ... 

Relation (7.83) holds only for the activity coefficient as defined in equation (7.82), i.e., based on the number density scale. However, it is quite a simple matter to use any other activity coefficient to extract the same information. Let Cs be any other concentration units (e.g., molality, mole fraction, etc). We write the general conversion relation between Cs and ps symbolically as... 

For aqueous-phase chemical reactions the commonly used concentration unit is mol L 1. Aqueous solutions in cloud and raindrops are characterized by concentrations in the range of pmolL. For a dilute aqueous solution molality (mol kg-1) is approximately equal to molarity (mol L-1). The conversion between molar concentration c and molality m is... 

Irving Langmuir, the Nobel prize-winning industrial physical chemist who worked at General Electric, built an elegant structure upon this foundation in kinetic theory. He reasoned that not every molecule would adsorb, but only some would do so. Furthermore, one reason for this was that to be adsorbed there should be a site for adsorption to occur. It stands to reason then that on the basis of mass action, the rate of adsorption should be proportional to the concentration of molecules in the gas phase and to the number of sites available on the surface. Additionally, the rate should be related at any time to the number of sites not covered at that time rather than to the total number of sites present per unit area. Conversely, and again by the principle of mass action, the rate of desorption should be proportional to the number of sites currently occupied at that time. Using ka and kd as the proportionality constants (that we will call the rate constant for adsorption and desorption, respectively), we can write the net rate of adsorption for gas phase species i as the difference between the rate of adsorption and the rate of desorption ... 

In all calculations the molar masses given in the top of Table I were used. First of all, the effects of variations in the concentration of trifunctional monomers were determined, as exemplified by the nine formulations of Table I and the resulting prepolymer characteristics after full conversion given in Table II. Formulations FIO to F40 result in branched prepolymers, which are cured in the third stage by difunctional monomers. On the other hand, formulations FOO to F04 result in the same linear prepolymer, which is subsequently cured with various mixtures of di- and trifunctional monomers. The number average functionalities of PI (and P2) and of the mixtures of E and F monomers are varied systematically between 2.0 and 2.4. Therefore, the only difference between formulations FjO and FOj is the stage in which the branching units are added. 

To decide which value of R to use when you convert between and K, you can reason as follows. involves molar concentrations, for which the units are mol/L involves pressures expressed in atm. Thus the appropriate value of R to use for these conversions... 

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