Solubility salt 2008

Solubility salt 2008 - THE SOLUBILITY OF A SALT IN WATER AT...

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THE SOLUBILITY OF A SALT IN WATER AT VARIOUS TEMPERATURES ©2008, 2007, 1995, 1991 by David A. Katz. All rights reserved. Permission for academic use provided the original copyright is included. OBJECTIVE To measure the solubility of a salt in water over a range of temperatures and to construct a graph representing the salt solubility. THEORY One of the most common forms of a homogeneous mixture is a solution. The one component of a solution, which is usually present in the greatestr proportion, is called the solvent . The other components, present on a smaller scale, called solutes , are considered to be dissolved in the solvent. There are a number of different kinds of solutions: gases in gases (example: air), liquid in liquids (example: gasoline), gases in liquids (example: carbonated soft drinks), solids in solids (example: alloys such as brass), and solids in liquids (example: salt water). This experiment will involve a solution formed with a solid solute (a chemical salt) and a liquid solvent (water). If the properties of a solution remain constant, the system of solute and solvent is considered to be at equilibrium. Obviously, if the solid is disappearing into the solvent, the system is not at equilibrium. Solubility of a solid in a liquid is dependent on temperature, thus, at a given temperature, only a certain maximum amount of solute will dissolve in a given amount of solvent. Beyond that amount of solute, no more will dissolve and excess solute will remain in the solid form, settling to the bottom of the solution container. This maximum amount of dissolved solute, expressed quantitatively, is given in units of grams of solute/100 g of solvent. Such a solution is termed a saturated solution , since it is holding all the solute it can hold at that temperature. Experiments show that when excess solute is in contact with a saturated solution, an equilibrium is established in which solute is continually dissolving in amounts just equal to the solute separating from solution (crystallization) (see Figure 1). When saturated solutions of solid solutes are prepared at elevated temperatures and then permitted to cool, the excess solute usually separates from the solution by crystallizing. However, if a saturated solution is prepared at an elevated temperature and any excess, undissolved solute is removed, crystallization often does not take place when the solution is allowed to cool undisturbed. The solution can contain more of the solute than normally is held in equilibrium with the solid state. Such solutions are said to be supersaturated . A supersaturated solution is a system in a metastable (unstable) condition. Agitation of the solution or the addition of a seed crystal of the solute may start crystallization of the excess solute. After crystallization, a saturated solution remains.
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This note was uploaded on 12/07/2011 for the course CHEM 152 taught by Professor Staff during the Spring '08 term at Pima CC.

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Solubility salt 2008 - THE SOLUBILITY OF A SALT IN WATER AT...

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