Concentration expression mass/volume

In molecular weight determinations it is conventional to dissolve a measured mass of polymer m2 into a volumetric flask and dilute to the mark with an appropriate solvent. We shall use the symbol Cj to designate concentrations in mass per volume units. In practice, 100-ml volumetric flasks are often used, in which case C2 is expressed in grams per 100 ml or grams per deciliter. Even though these are not SI units, they are encountered often enough in the literature to be regarded as conventional solution units in polymer chemistry. 

Solution concentration may be expressed as a percentage, which is the amount of solute dissolved per 100 units of solvent. It may be expressed as mass %, mass/volume %, or volume/volume %. Know how to calculate the appropriate percentage concentration for a solution. 

Note 1 The solute concentration is most frequently expressed in terms of mass concentration, molality or volume fraction. If expressed in terms of mass concentration or molality, the corresponding refractive index increments are referred to as specific or molal refractive index increments, respectively. 

The Einstein theory shows that volume fraction is the theoretically favored concentration unit in the expansion for viscosity, even though it is not a practical unit for unknown solutes. As was the case in the Flory-Huggins theory in Chapter 3, Section 3.4b, it is convenient to convert volume fractions into mass/volume concentration units for the colloidal solute. According to Equation (3.78), 0 = c(V2/M2), where c has units mass/volume and V2 and M2 are the partial molar volume and molecular weight, respectively, of the solute. In viscosity work, volumes are often expressed in deciliters —a testimonial to the convenience of the 100-ml volumetric flask In this case, V2 must be expressed in these units also. The reader is advised to be particularly attentive to the units of concentration in an actual problem since the units of intrinsic viscosity are concentration when the reduced viscosity is written as an expansion of powers of concentration c. (The intrinsic viscosity is dimensionless when the reduced viscosity is written as an expansion of powers of volume fraction 0.) With the substitution of Equation (3.78), Equation (42) becomes... 

The concentration expressed as the mass of the analyte in the test solution divided by the volume of the test solution. The term mass fraction should be used if the amount of the analyte is related to the mass of the sample. 

Standards can be expressed in various units, such as a load (mass/unit area), a dose (mass/body mass), or a concentration (mass/volume mass contaminant/mass soil). The use of a unit depends on the environmental compartment under consideration. We might consider the amount of pollution in water (a concentration), the consequences of equilibrium uptake by (or exposure to) a human (a dose), or the acceptable uptake by an ecosystem under steady conditions (the loading). The choice of unit depends on the point in a cycle or pollutant linkage at which we set the standard, as illustrated in Figure 3.1. 

Chemists often express the concentration of an unsaturated solution as the mass of solute dissolved per volume of the solution. This is different from solubility. It is usually expressed as a percent relationship. A mass/volume percent gives the mass of solute dissolved in a volume of solution, expressed as a percent. The mass/volume percent is also referred to as the percent (m/v). 

You need to calculate the concentration of the solution, in grams of solute dissolved in 100 mL of solution. Then you need to express this concentration as a mass/volume percent. 

You have learned about several different ways in which chemists express concentration mass/volume, mass/mass, and volume/volume percent parts per million and parts per billion and molar concentration. The Concept Organizer above summarizes what you have learned in this chapter so far. 

In aquatic systems, concentrations can also be expressed as mass per unit mass and in the oceans some trace constituents are present at concentrations of ng kg or pg kg More often, however, sample sizes are measured by volume and concentrations expressed as ng or pg In the case of freshwaters, especially, concentrations expressed as mass per litre will be almost identical to those expressed as mass per kilogram. As a kind of shorthand, however, water chemists sometimes refer to concentrations as if they were ratios by weight, thus, mg are expressed as ppm, pg as ppb and ng as ppt. This is unfortunate as it leads to confusion with the same units used in atmospheric chemistry with a quite different meaning. 

Paresthesia Abnormal physical sensations such as numbness, prickling, or tingling Particle A very small but discrete mass of solid or liquid matter Particle concentration Concentration expressed in terms of number of particles per unit volume of air or another gas... 

In addition to solubility, the concentration of a dissolved substance in a given solvent can be expressed in parts per notation, when low concentrations of a particular substance are still considered significant. In these cases the metric system is the most convenient way to express values as metric units increase stepwise as ten, hundred, thousand and so on. Typically this is given on the basis of mass but it can also be expressed by volume, mass/volume (m/v) ratio, or number of moles. For example A milligram (1 mg or 0.001 g) is one part per thousand of a gram (1000 mg or 1 g) or one part per million (ppm) of a kilogram (1000 000 mg or 1000 g). 

Mass concentration. Generally, two methods are used to express mass concentration mass of solute per unit volume of the mixture (m/v basis) and mass of the... 

Most laboratory analysis methods measure concentration. The choice of units for concentration depends in part on the medium and in part on the process that is being measured or described. In water, a common expression of concentration is mass of chemical per unit volume of water. Many naturally occurring chemicals in water are present at levels of a few milligrams per liter (mg/liter). The fundamental dimensions associated with such a measurement are [M/L3]. The letters M, L, and T in square brackets refer to the fundamental dimensions of mass, length, and time, which are discussed further in the Appendix. For clarity in this book, specific units, such as (cm/hr) or (g/m3), either are free-standing or are indicated in parentheses, not in square brackets. 

For any case in which F is zero, a definite reproducible solubility equilibrium can be reached. Complete representation of the solubility relations is accomplished in the phase diagram, which gives the number, composition, and relative amounts of each phase present at any temperature in a sample containing the components in any specified proportion. Solubilities may therefore be expressed in any appropriate units of concentration, such as the quality of the solute dissolved (defined mass, number of moles) divided by the quantity either of the solvent (defined mass, volume, or number of moles) or of the solution (defined mass, volume, or number of moles). Jacques et al. (1981) have provided a compilation of the expressions for concentration and solubility. 

When analyzing the thermodynamic properties of polymer solutions, it is sufficient to consider only one of the components, which for reasons of simplicity is normally the solvent. For many physicochemical calculations, especially when dealing with dilute solutions, it is convenient to express the solvent activity as a power series in terms of polymer concentrations C2 in mass/volume units. 

Note that the concentration expressed as for e.g. ppb, is by volume. For liquids suspended as an aerosol, expressing the concentration on a mass per unit volume basis is a natural approach. However, the following approach is sometimes used. 

In the case of smaller concentrations pphm (parts per hundred million) and ppb (parts per billion where billion = I09) can also be used. Another possibility to express the atmospheric level of trace gases and aerosol particles is the mass concentration", which gives the mass of a substance per unit volume of air. The dimension of the mass concentration is g cm-3 or more frequently /ig m 3. This quantity is a function of the temperature and pressure since the air volume in the denominator depends upon these physical parameters. Thus, it is reasonable to express its values in /rg m 3 STP (standard temperature and pressure). In this book we will use concentrations expressed mainly in ppm and in ng m-3 STP. Table 4... 

Three ways of quantitatively expressing the concentration of a solution will be presented here Mass/mass percent, %(m/m), mass/volume percent, %(m/v), and molarity, M. A fourth, molality, will appear later in this chapter. You should know an interesting fact about concentrations. No matter what size sample of a solution you have, be it a teaspoonful or a bucketful, the concentration is the same for both. This is because concentrations are stated in terms of the amount of solute in a fixed amount of solvent 100 g, 100 mL, or 1.00 L. It s like density. The density of mercury is 13.6 g/mL. If I have 100 mL or three drops of mercury, the density of mercury is still 13.6 g/mL. Neither density nor concentration depends on the size of the sample. 

Air is ma.de up primarily of N2, O2, and Ar, which comprise 99.9% of dry air. There is a variable amount of water vapor, and many minor and trace gaseous components, as well as aerosol and particulate species. Table 26.1 lists some atmospheric gaseous components of environmental interest, along with representative concentrations in the troposphere. Typically, gaseous concentrations are expressed as mixing ratios, that is, volume/volume concentrations. A 1-ppm concentration represents 1 volume in 10 volumes of air. Such mixing ratios are independent of temperature and pressure. Environmental effects, though, may be quantitatively related to mass concentrations, and concentrations may be reported as mass per unit volume, usually mg/m of air, under specific conditions of temperature and pressure. Aerosols and particulates are reported in this way. 

In dilute solution, the total number of moles of solute and solvent in unit volume will approach Ci, the molar concentration of solvent. Then the mole fraction X2 of solute can be expressed as X2 = C2/(Ci+C2) - C2/Ci, where C2 is the molar concentration of solute. If the mass/volume concentration of solute is C2 and M2 is the molecular weight of... 

The concentration of a solution can be expressed in different terms (molarity, molality, parts by mass, parts by volume, and mole fraction). Because a concentration is a ratio involving mass, volume, and/or amount (mol), the various terms are interconvertible. 

M NaCl has the same concentration as 1.0 mL of 0.1 M NaCl. Concentration is most often expressed as the ratio of the quantity of solute to the quantity of solution, but sometimes it is the ratio of solute to solvent. Because both parts of the ratio can be given in units of mass, volume, or amount (mol), chemists employ several concentration terms, including molarity, molality, and various expressions of parts of solute per part of solution (Table 13.4). 

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