Concentration units used

Normality is an older unit of concentration that, although once commonly used, is frequently ignored in today s laboratories. Normality is still used in some handbooks of analytical methods, and, for this reason, it is helpful to understand its meaning. For example, normality is the concentration unit used in Standard Methods for the Examination of Water and Wastewaterf a commonly used source of analytical methods for environmental laboratories. 

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. 

Notice that this equation uses kilograms of solvent, not solution. The other concentration units use mass or volume of the entire solution. Molal solutions use only the mass of the solvent. For dilute aqueous solutions, the molarity and the molality will be close to the same numerical value. 

Do not forget that nearly all the concentration units use the total for the solution in the denominator. For these units it is important to remember to combine the quantities for the solvent and all solutes present. Molal concentrations are exceptions. Molality uses only the kilograms of solvent in the denominator. Do not make the mistake of using the entire solution in the denominator for molal concentrations. 

Some concentrating units use chemical solvents some use mechanical methods, sometimes coating a surface with a material for which the quarry molecules have a distinct affinity. One of the most convenient characteristics of explosive molecules is the way temperature affects their adhesion to surfaces. They adhere readily to cool surfaces but are easily released by a modest rise in temperature. Concentrating units often exploit this characteristic by alternately chilling and warming a collection surface. The surface is chilled while sampling and warmed for sensing. 

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... 

Equation 16-7 not only shows the simple way that K, depends on temperature, it also shows a simple way to determine the enthalpy change for a reaction. By determining the value of e at several different temperatures, and then plotting log Ke versus 1 IT, we should get a straight line whose slope is -AE/2.3.R. If the reaction is exothermic LH is negative), the slope will be positive if the reaction is endothermic (A/f is positive), the slope will be negative (Figure 16-1). Equation 16-7 applies to all chemical equilibria and is independent of the concentration units used either Kp or < can be use(j equally... 

B 9. The concentrations of cholesterol, glucose, and urea in blood from a fasting individual are listed below in units of mg/100 mL (sometimes called mg%). These are standard concentration units used in the clinical chemistry lab. Convert the concentrations to mM. cholesterol—200 mg% glucose-75 mg% urea-20 mg%... 

The value of the partition coefficient in this derivation, AT, is the ratio of the concentration of solute in the coating to the concentration of solute in the ambient (vapor) phase, with all concentrations being expressed in units of mass of solute per unit volume. Alternative expressions for the partition coefficient can be derived for concentration units of (moles of solute/coating volume) or (mass of solute/coating mass), or on a mole fraction basis. The value of K will be dependent on the concentration units used. For our purposes in the remainder of discussion, will refer specifically to the partition coefficient using the concentration units of mass per unit volume as described above. 

F cumene, C and dl-lsopropylbenzenes, D. Equation (4e) defines the equilibrium constant, K, for reaction (3). The concentration units used are moles of component per unit mass of total reactor fluid. Over the range of conditions used In this work, the reactor fluid was a liquid phase maintained by sufficient pressure at all conditions of temperature and composition. 

Let us first derive the units of the overall mass transfer coefficients when the concentration units used are in mole fractions. Let the overall mass transfer coefficient for the gas side be Kyf and that for the liquid side be K. Gd Y is mole of solute flowing per unit time. Mass transfer is a process where mass crosses an area perpendicular to the direction of motion of the solute particles. This area is the contact area for mass transfer. Let the differential area be designated as dA. Thus, in terms of mass transfer, Gd[Y] is equal to j,/([y/] - y )dA. From this expression, the dimensions of Kyf are mole per unit time per unit mole fraction per unit square area or MItImole fraction-1. In an analogous manner, Ld X is equal to ] -... 

The valne of R depends upon the unit used for the other variables. Table 11.1 gives its various values and units, along with the units used for AH and T. By convention, the concentration units used in the calculation of K are in gmmols/L. 

R Value R Units K Concentration Units Used AH° Units T Units... 

Equations (7-13) and (7-14) are dimensionless all units cancel on each side of the equality sign. Thus the reactivity ratios are indicated to be independent of dilution and of the concentration units used. The reactivity ratios for a particular monomer pair should be the same in bulk and in dilute solution copolymerizations. 

Molality, molarity, mole fraction —> Different concentration units used for quantitative treatment of... 

Molality and normality are other concentration units used in chemistry. 

The concentration unit used for analysis is molarity, that is, the number of moles of solute per liter of solution. It should be noted that the molarity involves a weight/volume ratio, and that the volume involved is that of the total solution. In order to determine the molarity of the system being considered here, one must know the density of the solution. In general, this property cannot be determined from the densities of the individual components but must be found in an independent experiment. The density of acetonitrile-water solutions as a function of the weight fraction of acetonitrile is shown in fig. 1.1. From these data one finds that the density of the solution made of 10 g acetonitrile and 90 g water is 0.979 g mL at 25°C. Thus, the volume of the same solution is 102.15 mL and the corresponding molarity, 0.2437/0.10215 = 2.386 M. The relationship between the molarity cb and mole fraction xb is... 

Because of the inconvenient nature of the standard state defined above, the concentration units used to describe the concentration dependence of the chemical potential are usually different. More convenient choices for concentration are molality and molarity. When the solution is dilute the relationship between mole fraction and molality is quite simple (see equation (1.2.3)). In terms of molality, the expression for the concentration dependence of the chemical potential of component B becomes... 

This equilibrium or partitioning of a solute between micelles and the aqueous surroundings has not been uniformly described in the literature. We speak of distribution coefficient or constant, partition coefficient or constant, or equilibrium constant to describe equilibria that are the same qualitiatively speaking. However, the definition of the above-mentioned coefficients or constants varies. In this chapter we refer to the process as a partitioning of a molecule between micelles and the aqueous surroundings, and we term it the partition coefficient regardless of the concentration units used to define it. 

To make Equation (8.21) tractable for design purposes, it is necessary to make the assumption that thermodynamic equilibrium exists at the interface, i.e., yl = Ki or y,, /x, int = Ki, where Kj is the conventional thermodynamic equilibrium ratio and the asterisks denote an equilibrium composition. Note that the equilibrium designation depends on the concentration units used. For example, if gas concentrations are in partial pressures and liquid compositions are in molar concentrations, a Henry s law coefficient. Hi = must be used. 

Another concentration unit used by chemists is molality, symbolized by an italic, lowercase m. It is defined as the number of moles of solute per kilogram of solvent. The unit of molality is molal, symbolized by a regular (not italic) m. (Some texts use regular m for both.) Note well the differences between molarity and molality the denominator of molality involves a mass not a volume, and it is the mass of the solvent, not the solution. Great care must be taken to avoid confusing molarity and molality because their names as well as their units and symbols are so similar. We must be sure to use the standard notation so that we do not confuse ourselves ... 

Before leaving this section, one comment about the concentration units used should bp made. Molality, which we have used here. and indicated by.the symbol M, is concentration expressed as moles of solute per kilogram of solvent. Molarity, defined as the number of moles of solute per liter of solution, is also a commonly used concentration unit. However, because the volume of a solution varies with composition and with temperature, molarity can be more difficult to deal with than molality, which is... 

Care should be taken when comparing the formulas for the retardation factor, since the mathematical form critically depends on the concentration units used. For example, concentration of adsorbed solute in the hydrology literature is measured in weight of adsorbed material per volume or mass of the fluid, rather than the solid ... 

Our discussion in the previous sections has been based on a Cartesian coordinate system using x, y, and z as the coordinates and the molar concentration of species as the dependent variable. Other coordinate systems and concentration units used in chemical transport models are outlined below. 

Consider now a solution made up of i species. The two basic concentration units used are the mass concentration [density] and molar concentration., defined, respectively, by... 

Chemical concentrations are given in different units depending on the field of technology they come from. They can be converted from one to another, if need be, through suitable conversion equations given in Johnson (1999). Numerical values of equilibrium constants depend on the concentration units used, so the conventional concentrations are given in moles per liter. Other commonly used concentration units are ... 

Conduction of electric current in conductors can be electronic or ionic, depending on the type of charges involved. Electronic conduction is found in all metals and also in certain other nonmetals. Ionic conductors are also known as electrolytes. Substances that ordinarily are not conducting can produce ionic conduction after being dissolved in water or another solvent (e.g., electrolyte solution and weak electrolyte ). The relative amount of substance present in a solution or a mixture is known as its concentration. The different concentration units used mostly are molarity, molality, normality, and mole fraction. The acidity or basicity of a solution is measured by a relative measurement called the pH of solution. It is defined as the cologarithm of the activity of dissolved hydrogen ions (H" "). Pure water is said to be neutral. The pH for pure water at 25 °C (77 °F) is close to 7.0. Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are said to be basic or alkaline. 

The quantity that changes most in example 1 is Ac neither S nor soluble substances considerable changes can occur in all expressions of supersaturation depending on the concentration units used, as seen in example 2 where [Pg.126]

These assumptions control the concentration units used to plot the McCabe-Thiele diagram. If total flows are constant, the solute mass balance is written in terms of fractions, and fractions are plotted on the McCabe-Thiele diagram. If flows of nontransferred species are constant, ratio units must be used, and ratios are plotted on the McCabe-Thiele diagram. 

Chapter 5 discusses the unit problem that exists in the literature listing micellar partition coefficients. The Armstrong-Nome equation gives the PwM solute-micelle affinity coefficient. It is a dimensionless coefficient but valid for one surfactant molecule. The true solute micellar partition coefficient is N with N the micelle aggregation number. Equations 5.8 and 5.9 give an equivalent coefficient whose dimension depends on the concentration unit used. All equations relate linearly 1/k, the retention factor, with [M], the micellar concentration (= surfactant concentration - cmc) in mol/L or in g/L. The relations between the two coefficients are ... 

Using the same settings as obtained in step 2, run the same procedure on pure water. The blank should be very small, if detectable at all. Usually with the 500mL vessel there is a small but significant blank (ca. 0.3 ng). Record this blank and convert it to concentration units using the sensitivity constant from step 2. 

For the percent and concentration units used in the text without designation, they correspond to usage in the original paper. 

It is probably regrettable that the unit of enzyme activity is not the mole/second, which is more in line with the concentration units used by physicists and chemists. 

Ai lication of the Freundilch equation The Freundlich equation can frequently be applied to adsorption of this type, particularly since small adsorbable solute concentrations are usually involved This can be written in the following form for the concentration units used here. 

When appraising results of solubilization studies one must always take into account the concentration units used. Units varying from grams solubilizate per 100 ml surfactant solution to moles solubilizate per gram micelle interior appear in the literature. 

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