Dissolved substances

The process of extraction with solvents is generally employed either for the isolation of dissolved substances from solutions or from solid mixtures or for the removal of undesired soluble impurities from mixtures. The latter process is usually termed washing. 

Although spindles are caUbrated for pure sucrose, other components are normally present in sugar that contribute to the density, such as ash and invert. Because the densities of these components are not much different from that of sucrose, the spindle value is considered a measure of total dissolved substances. 

Introduction Insoluble hquids may be brought into direct contact to cause transfer of dissolved substances, to allow transfer of heat, and to promote chemical reaction. This subsection concerns the design and selection of equipment used for conduc ting this type of liquid-hquid contact operation. 

Finally, we may note that every solution exerts a vapor pressure less than that of the pure solvent at the same temperature. Corresponding to this vapor-pressure lowering is an equivalent boiling-point raising. Dissolved substances lower the vapor pressure of the solvent. Such reduction increases with the concentration of solute. Since a solution boils when its vapor pressure reaehes that of its surroundings, it must be heated to a temperature above the boiling point of the pure... 

Weight ratio G/G dissolved substance extracted by washing liquid to the substance in the cake before washing = 0.98... 

Through these processes dissolved substances and/or finely dispersed particles can be separated from liquids. All five technologies rely on membrane transport, the passage of solutes or solvents through thin, porous polymeric membranes. 

To best understand adsorptive solvent recovery we have to consider some fundamentals of adsorption and desorption. In a very general sense, adsorption is the term for the enrichment of gaseous or dissolved substances (the adsorbate) on the boundary surface of a solid (the adsorbent). On their surfaces adsorbents have what we call active centers where the binding forces between the individual atoms of the solid structure are not completely saturated. At these active centers an adsorption of foreign molecules takes place. 

Adsorption The gathering of a gas, liquid, or dissolved substance on the surface or interface zone of another substance. 

Solution A liquid mixture of dissolved substances, displaying no phase separation. Specific gravity Weight of a particle, substance or chemical solution in relation to an equal volume of water. 

Rotation of Tartaric Acid.—The s]iccific loi.iiion of a dissolved substance can be calculated from the rotation of tli<-solution if the conccntiation is known. The foi inula to be for this purpose is —... 

This method ctui be applied to a number of pollutmits, including suspended and dissolved substances, as well as to heat balance computations. 

But, since the specific rotation of dissolved substances vary with the concentration and the nature of the solvent, these data should always be given when the specific rotation is quoted. 

More complicated and less known than the structure of pure water is the structure of aqueous solutions. In all cases, the structure of water is changed, more or less, by dissolved substances. A quantitative measure for the influence of solutes on the structure of water was given in 1933 by Bernal and Fowler 23), introducing the terminus structure temperature, Tsl . This is the temperature at which any property of pure water has the same value as the solution at 20 °C. If a solute increases Tst, the number of hydrogen bonded water molecules is decreased and therefore it is called a water structure breaker . Vice versa, a Tsl decreasing solute is called a water structure maker . Concomitantly the mobility of water molecules becomes higher or lower, respectively. 

This usage of the word saturated shows that chemists, like other people, sometimes use the same word with two entirely different meanings. On p. 164 this word was used to describe a solution which contains the equilibrium concentration of a dissolved substance. As used here, in reference to organic compounds, it means that all bonds to carbon are single bonds and they are all formed with hydrogen or other carbon atoms. 

See also Oxidation, Reduction). Some dissolved substances in water occur either in an oxidized or a reduced form, and their state can be changed by either the acquisition of electrons (reduction) or the loss of electrons (oxidation). This transfer system is an reduction-oxidation system, or redox. (Red. - Oxid. n+ = ne—, where n is number of electrons involved), and can be used to measure and... 

Chemists need to be able to specify the composition of mixtures quantitatively. For example, a chemist may need to monitor a pollutant, administer a dosage, or transfer a known amount of a solute. In this section we examine the properties and types of mixtures as well as how to use the molar concentration of a dissolved substance to analyze solutions quantitatively. 

FIGURE G.3 Solutions are homogeneous mixtures in which one substance, the solvent (here water), is usually in large excess. A dissolved substance is called a solute. 

Now that we have reviewed some basic aspects of the chemical composition of the ocean we can turn to a more fundamental question. What processes determine the composition of the ocean Current evidence suggests that rivers are the most important contributors of dissolved substances to the ocean. Since there is geologic evidence that the concentration and composition of the ocean has been relatively constant over the last 1.5 billion years, we must conclude that the river input must be balanced by removal. 

---