Theory of dilute solution

Thesis Overview

<p> </p><p><strong>Introduction:</strong></p><p>The knowledge of the laws of solutions has been said, to be important because almost all the chemical processes which occur in nature, whether in animal or vegetable organisms, or in the non-living surface of the earth, and also those which are carried out in the laboratory, take place between substances in solution. For example, a sound judgment regarding physiological processes is impossible without this knowledge; and this holds true for the greater number of the scientifically and technically important reactions. Solutions are more important than gases, for the latter seldom react together at ordinary temperatures, whereas solutions present the best conditions for the occurrence of all chemical processes (Homer, 1980).</p><p>A dilute solution has a low concentration of the solute compared to the solvent. The opposite of a dilute solution is a concentrated solution, which has high levels of solute in the mixture.</p><p>Dilute solutions containing non-volatile solute exhibit the following properties:<br>(1) Lowering of the Vapour Pressure<br>(2) Elevation of the Boiling Point<br>(3) Depression of the Freezing Point<br>(4) Osmotic Pressure</p><p>The essential feature of these properties is that they depend only on the number of solute particles present in solution. Being closely related to each other through a common explanation, these have been grouped together under the class name Colligative Properties (Greek colligatus = Collected together) (Bahl, et al., 2012).</p><p>Physical properties can be divided into two categories. Extensive properties (such as mass and volume) depend on the size of the sample. Intensive properties (such as density and concentration) are characteristic properties of the substance; they do not depend on the size of the sample being studied. This section introduces a third category that is a subset of the intensive properties of a system. This third category, known as colligative properties, can only be applied to solutions. By definition, one of the properties of a solution is a colligative property if it depends only on the ratio of the number of particles of solute and solvent in the solution, not the identity of the solute.</p><p>A colligative property may be defined as one which depends on the number of particles in solution and not in any way on the size or chemical nature of the particles. In other words, colligative properties are a set of solution properties that can be reasonably approximated by assuming that the solution is ideal.<br>Here we consider only properties which result from the dissolution of nonvolatile solute in a volatile liquid solvent. They are essentially solvent properties which are changed by the presence of the solute. The solute particles displace some solvent molecules in the liquid phase and therefore reduce the concentration of solvent, so that the colligative properties are independent of the nature of the solute.<br>For a given solute-solvent mass ratio, all colligative properties are inversely proportional to solute molar mass.</p><p>Measurement of colligative properties for a dilute solution of a non-ionized solute such as urea or glucose in water or another solvent can lead to determinations of relative molar masses, both for small molecules and for polymers which cannot be studied by other means. Alternatively, measurements for ionized solutes can lead to an estimation of the percentage of dissociation taking place.<br>Colligative properties are mostly studied for dilute solutions, whose behavior may often be approximated as that of an ideal solution.</p> <br><p></p>