Solvation Process

Topics: Solubility, Temperature, Solvent Pages: 5 (1489 words) Published: March 3, 2013
GOMEZ, Gina Melissa N.SY1213

also sometimes called dissolution, is the process of attraction and association of molecules of a solvent with molecules or ions of a solute. As ions dissolve in a solvent they spread out and become surrounded by solvent molecules.

As an ionic compound dissolves, such as NaCl, the ions become surrounded by the solvent, say H2O(water) molecules. The ions are said to be 'solvated' as they become surrounded by the solvent, similar to a hoard of bees surrounding a nest. The solvation process helps stabilize the ions in solution and prevents cations and anions from recombining. Furthermore, because the ions and their shells of surrounding water molecules are free to move about, the ions become dispersed uniformly throughout the solution.

Factors that Affect Solubility

Solute-Solvent Relations
The relation between the solute and solvent is very important in determining solubility. Strong solute-solvent attractions equate to greater solubility while weak solute-solvent attractions equate to lesser solubility. In turn, Polar solutes tend to dissolve best in polar solvents while non-polar solutes tend to dissolve best in non-polar solvents. In the case of a polar solute and non-polar solvent (or vice versa), it tends to be insoluble or only soluble to a miniscule degree. The general rule to remember is "Like Dissolves Like".

Common-Ion Effect
The common-ion effect is a term that describes the decrease in solubility of an ionic compound when a salt that contains an ion that already exists in the chemical equilibrium is added to the mixture. This effect best be explained by Le Chatelier's Principle. Imagine if we were add the slightly soluble ionic compound Calcium Sulfate  into water. The net ionic equation for the resulting chemical equilibrium would be: Calcium Sulfate is slightly soluble meaning that at equilibrium, most of the calcium and sulfate exists in the solid form of Calcium Sulfate. Let's say that we now add the soluble ionic compound Copper Sulfate ( ) into the solution. Copper Sulfate is soluble, therefore its only important effect on the net ionic equation is the addition of more Sulfate  ions. The Sulfate ions dissociated from Copper Sulfate are already present (common to) in the mixture from the slight dissociation of Calcium Sulfate. Thus, this addition of Sulfate ions places stress on the previously established equilibrium. Le Châtelier's Principle dictates that the additional stress on this product side of the equilibrium results in the shift of equilibrium towards the reactants side in order to alleviate this new stress. In shifting towards the reactant side, we can see that from the above equation that the solubility of the slightly soluble Calcium Sulfate is reduced even further.   

Temperature changes affect the solubility of Solids, Liquids and Gases differently. However, those effects have only finitely determined for Solids and Gases.

The effects of temperature on the solubility of solids differ depending on whether the reaction is endothermic or exothermic. Using Le Chatelier's Principle, we can determine the effects of temperature in both scenarios. First, imagine an endothermic reaction (heat is on the reactants side where the solid is). Increasing the temperature would result in stress on the reactants side from the additional heat. Le Châtelier's Principle predicts that the system would shift towards the product's side in order to alleviate this stress. By shifting towards the product's side, more of the solid is dissociated when equilibrium is again established - which equates to increased solubility. Second, imagine an exothermic reaction (heat is on the products side where the dissociated ions from the solid are). Increasing the temperature would result in stress on the products side from the additional heat. Le Châtelier's Principle predicts that the system would shift towards the reactant's...
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