Solutions qualitative concentration terms

There are many ways of expressing the relative amounts of solute(s) and solvent in a solution. The terms saturated, unsaturated, and supersaturated give a qualitative measure, as do the terms dilute and concentrated. The term dilute refers to a solution that has a relatively small amount of solute in comparison to the amount of solvent. Concentrated, on the other hand, refers to a solution that has a relatively large amount of solute in comparison to the solvent. However, these terms are very subjective. If you dissolve 0.1 g of sucrose per liter of water, that solution would probably be considered dilute 100 g of sucrose per liter would probably be considered concentrated. But what about 25 g per liter—dilute or concentrated In order to communicate effectively, chemists use quantitative ways of expressing the concentration of solutions. Several concentration units are useful, including percentage, molarity, and molality. 

LeChateher s principle (Section 18.3) allows us to make qualitative predictions about the effects of changes of conditions on an equihbrium system but does not ahow quantitative calculations. However, at equihbrium at a given temperature, a certain ratio of concentration terms is very nearly constant for all solutes and gases involved in any given reaction. (Solids and pure liquids are not included in the ratio.) Because it is not exactly constant, we will use two or at most three significant digits in equihbrium constant calculahons. For the general reaction... 

Because a mixture, unlike a chemical compound, has a variable composition, the relative amounts of substances in a solution must be specified. The qualitative terms dilute (relatively little solute present) and concentrated (relatively large amount of solute) are often used to describe solution content. However, we need to define solution composition more precisely to perform calculations. For example, in dealing with the stoichiometry of solution reactions in Chapter 4, we found it useful to describe solution composition in terms of molarity, or the number of moles of solute per liter of solution. 

These equations differ from those for dilute solutions by the term (1—6c) in the denominator. The change in the vapour pressure, and in the boiling point and freezing point, is therefore relatively greater in concentrated than in dilute solutions. This result is confirmed qualitatively by experiment in almost every case, as a review of the literature of the subject will show (see in particular the researches of Abegg, Auwers, and others). It is clear from the primitive nature of the underlying assumptions that the above equations can only be accurate for a limited range of concentration. 

Suppose you re a worker in a hospital pharmacy lab and you must prepare a salt solution that matches the salt concentration of a patient s blood. You need to measure things carefully. Blood is a dilute salt solution, but the term dilute gives only qualitative information. In this case, you need a quantitative concentration unit. 

The oxidative deterioration of most commercial polymers when exposed to sunlight has restricted their use in outdoor applications. A novel approach to the problem of predicting 20-year performance for such materials in solar photovoltaic devices has been developed in our laboratories. The process of photooxidation has been described by a qualitative model, in terms of elementary reactions with corresponding rates. A numerical integration procedure on the computer provides the predicted values of all species concentration terms over time, without any further assumptions. In principle, once the model has been verified with experimental data from accelerated and/or outdoor exposures of appropriate materials, we can have some confidence in the necessary numerical extrapolation of the solutions to very extended time periods. Moreover, manipulation of this computer model affords a novel and relatively simple means of testing common theories related to photooxidation and stabilization. The computations are derived from a chosen input block based on the literature where data are available and on experience gained from other studies of polymer photochemical reactions. Despite the problems associated with a somewhat arbitrary choice of rate constants for certain reactions, it is hoped that the study can unravel some of the complexity of the process, resolve some of the contentious issues and point the way for further experimentation. 

The solute and solvent molecules present in any solution have different intensities of attractive force fields, and also have different molecular volumes and shapes. A concentration difference between the surface region and the bulk solution occurs because the molecules that have the greater fields of force tend to pass into the interior, and those with the smaller force fields remain at the surface. The Gibbs surface layer of a solution is more concentrated in the constituents that have smaller attractive force fields, and thus whose intrinsic surface free energy is smaller than the interior. As we stated in Section 3.3, this concentration difference of one constituent of a solution at the surface is termed adsorption. In qualitative terms, if the solution has a smaller surface tension than its pure solvent, the solute is concentrated in the surface layer indicating a positive adsorption according to... 

The concentration of a solution can be expressed either qualitatively or quantitatively. The terms dilute and concentrated are used to describe a solution qualitatively. A solution with a relatively small concentration of solute is said to be dilute one with a large concentration is said to be concentrated. Chemists use various ways to express concentration quantitatively, and we examine several of these next. 

The qualitative explanation of the observed relaxation time data in dilute metal-ammonia solutions in terms of the cavity model is thus quite satisfactory. One does not have to consider the monomers in solutions with concentration equal to and less than O.OIM because the monomer concentration is lower by about a factor of... 

The general term concentration refers to the quantity of solute in a standard qiran-tity of solution. Qualitatively, we say that a solution is dilute when the solute concentration is low and concentrated when the solute concentration is high. UsiraUy these terms are used in a comparative sense and do not refer to a specific concentration. We say that one solution is more dilute, or less concentrated, than another. However, for commercially available solutions, the term concentrated refers to the maximum, or near maximum, concentration available. For example, concentrated aqueous ammonia contains about 28% NH3 by mass. 

Equation 10 does not provide an adequate representation of the data. First, the rate constants calculated using this equation for experiments carried out at a pH greater than 10 are 15-20% smaller than the experimentally determined values. A second, and perhaps more compelling point is that Equation 10 does not correctly predict the dependence of rate upon Ns concentration in the more alkaline solutions. In qualitative terms what is observed is that the points in a plot of k vs. (N3-) approach linearity as the alkalinity of the solution is increased. A plot of the data in Table II obtained at pH 10.1 exhibits much less curvature than that presented in Figure 1. In a similar plot of the data in Table III obtained at a hydroxide ion concentration of 9 x 10r3M there is no detectable deviation from linearity. 

Gamma radiation can be used with macroscopic amounts of polymer. This is particularly welcome when polymers are not compatible with the GPC technique. Larger samples can be characterized by viscosity changes, usually measured in dilute solutions. All that is needed is a suitable solvent. If the Mark-Houwink parameters are known, it is possible to calculate viscosity-average molecular weight, Mv, from dilute solution viscosities. However, even the raw viscosity-concentration data in terms of the reduced viscosity may be enough to indicate the sensitivity of a given polymer in qualitative terms. The reduced viscosity at concentrations c is isp/c where t]sp — (solution viscosity — solvent viscosity)/solvent viscosity. 

Therefore, systems with two intermediate products treated in terms of kinetic equations (2.1.2) reveal at t —> oo only the stationary solutions n,i(oo). To observe non-trivial time behaviour of concentrations (meaning auto-oscillations or temporary structure), either more freedom degrees (accompanied with lost transparency of the qualitative analysis) or greater nonlinearity are required according to this theorem. 

It is immediately apparent that the Daniell cell differs from the zinc-chlorine battery in that the electrode materials (i.e., zinc and copper) of the former are both metals that normally exhibit a tendency to lose electrons. If the Daniell cell is to function as a battery, both metals cannot lose electrons—one must lose and the other must gain electrons. In this particular case, the issue can be decided, qualitatively at least, in terms of the order of activity of the metals. From Table 11.1, it should be recalled that zinc is much more active chemically than copper hence zinc might be expected to lose electrons more readily than copper if the metals are in contact with solutions of their ions at the same concentration. It may be inferred correctly that the reactions that occur when the Daniell cell serves as a source of electrical energy are as follows ... 

Expression (2.24) gives at least a qualitative description of the experimentally observed dependence of the initial quantum yield cpo of reaction on the concentration of MO acceptor. Indeed, the number (concentration) of dye ions MOad adsorbed at the surface of a colloidal particle before the light illumination, is a function of the MO concentration in a the solution and follows the dye adsorption isotherm at the same surface. Since MOad increases with increasing MO concentration, at surpassing of a certain concentration [MO], the ratio kj" K MO can appear to be much less that unity. If the Dad value is fixed, the second term of sum (24) becomes constant, and hence... 

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