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The Formations of Solutions

Objectives:

    1.    Explain the process by which solutions form.

    2.    Give the definition of solubility and explain how it is affected by various factors.

Key Terms:

    solvation        hydration        solubility

Notes: (15-3)

At some point you may have heard the phrase "like dissolves like" (polar dissolves polar and non-polar dissolves non-polar).  To understand this phenomena you must consider the intermolecular forces at work in a solution.  If the intermolecular forces present in the solution are compatible with the solvent, the solvent is considered soluble.

Solvation is the term given to the interaction between solvent and solute.  
If the solvent is water the reaction is called hydration - water is the most common polar solvent

(w3.rz-berlin.mpg.de/~mwolf/newfemtos/ eldyn/solvation.gif)

(omega.dawsoncollege.qc.ca/ ray/chemistry/nacl3.gif)

The solubility is the amount of solute that can dissolve in a solution at given conditions.  It depends on several conditions and is expressed in grams of solute per 100grams of solvent.

Temperature
Solubility of a gas is decreased with an increase in temperature
due to an increase in the kinetic energy of the molecules
Solubility of a solid is usually increased with an increase in temperature (endothermic reactions)
exception:
Exothermic - increasing temperature decreases solubility
an increase temperature has no effect on solubility when there is no temperature change for the solution
Pressure
Solubility of a gas is increased with and increase in pressure
Solubility of of a solid is usually unaffected by pressure

Factors affecting the rate of dissolving

Surface area
The greater the surface area the greater the rate of dissolving
Breaking the solute into smaller pieces increases the surface area
Stirring - increases the rate of dissolving by bringing solvent in contact with solute
Temperature - increases rate by increasing the kinetic energy of the solvent
 

 

Last modified: March 31, 2003