Concentration units interconversion

There is tolerable agreement between the values in Tables XVI and XVH, in such cases as direct or almost direct comparison is possible. Thus, for example, the Russian value of 48.52% by weight for the solubility of neodymium chloride at 30°C may be compared with 49.7% by Hinchey and Cobble, at 25°C. Indeed, if one follows the solubilities reported for neodymium chloride back to Matignon, the values at or near 25°C are all reasonably close together (178, 201, 205, 207, 258, 259). On the question of comparability, it may be remarked here that solubility comparisons are from time to time precluded by the preference of some authors for weight units, and of others for volume concentration units. When densities are also given, then of course interconversion is straightforward, but densities are by no means always available when needed. 

The most important aspect of eqn [4.1] is to recognize clearly the units involved, and to prepare the solution accordingly for molar concentrations you will need the relative molecular mass of the chemical, so that you can calculate the mass of substance required. Further advice on concentrations and interconversion of units is given on p. 45. 

Compile in tabular form data given in a problem. Students seem to grasp fairly well the complicated process of solving equilibrium problems. We believe this is because they have learned to organize the data in a table. We introduce them to a similar process for the interconversion of concentration units and for the determination of the nature of a solution after acids and bases are combined. 

E )q)lanation of the tabular method for the interconversion of concentration units... 

Length. It is when we come to units of length that the problems begin. The SI unit of length is the metre, m. Accordingly, the SI unit of concentration is mol m. Interconversion between concentration in mol m and concentration expressed in the more familiar units of mol dm is simple, i.e. 

Photoresponsive polymers can be obtained by introducing photochromic units, such as azobenzene or spiropyran groups, into the macromolecules of polymeric compounds. As described in Chapter 1 of this book, photochromic compounds can exist in two different states, such as two isomeric structures that can be inter-converted by means of a light stimulus, and the relative concentrations of which depend on the wavelength of the incident light. For instance, in azobenzene compounds, photochromism is due to trans-cis photoisomerization around the N=N double bond, while in spiropyran compounds photochromism involves interconversion between the neutral spiro form and the zwitterionic merocyanine form (Figure 1). 

A wide range of units is commonly used to express solution concentration, and confusion often arises in the interconversion of one set of units to another. Wherever possible throughout this book we have used the SI system of units. Although this is the currently recommended system of units in Great Britain, other more traditional systems are still widely used and these will be also described in this section. 

Both in this book and in medical practice, you will need to interconvert different units used for the weight and size of compounds and for their concentration in blood and other fluids. Table 1 provides definitions of some of the units used for these interconversions. 

In view of the frequent need to make interconversions of composition units it is recommended that, whenever solution concentration measurements are made, the density of the solution at the relevant temperature is also measured and recorded (see section 3.9). 

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