Section 11.02

The Solution Process

Introduction

"A solute will dissolve in a solvent if the solute particles have greater attraction for the solvent than they do for their fellow solute particles."-Haiku

Basically, the solute (thing being dissolved) will actually dissolve if the attraction between it and the solvent (stuff you're dissolving it with) is stronger than the attraction between the solute and itself. The solvent has to be able to pull the particles away from the solute in order to dissolve it.  They then mix and form a solution.

Water and Sodium Chloride

How soluble a thing is depends largely on its polarity. Solvents work best when they are similar in polarity to their solutes.  Neutral water molecules are dipolar, meaning that it is charged both positively and negatively at the same time on different places of the molecule.  Sodium chloride is an ionic compound held together by the attraction between the positive sodium ion and the negative chlorine ion.  

Mixing dipolar water with ionically bonded sodium chloride makes a solution.  The dipolar solvent pulls the ionic solute apart easily because they both have positive and negative charges and are of similar polarity.  The attraction between an ion, like sodium chloride, and a dipolar molecule, like water, is called an ion-dipole attraction.

Heat of Solution

The heat of a solution is the amount of heat energy absorbed or released when a solute dissolves in a specific amount of solvent.

Enthalpy

The enthalpy change in a liquid solution made from a liquid solvent and a solid solute can be calculated as:

ΔH(solution) = ΔH(1) + ΔH(2) + ΔH(3)

when:

  • ΔH(1) is the energy absorbed to spread out the particles of the solvent so that there is room for the solute to dissolve into it.  This is endothermic.
  • ΔH(2) is the energy absorbed to spread out the solute by dissolving so that it forms a solution.  This is endothermic.
  • ΔH(3) is the energy released when the solute and solvent mix together.  This is exothermic.

Quiz

  1. Contrast and define:  solution, solvent, solute.
  2. Give a general equation for an endothermic solution process and an exothermic solution process.  Tell which is which.
  3. What is an ion-dipole attraction?
  4. True or false:  Polarity is largely unrelated to how well a solute will dissolve.
  5. True or false:  A solute will dissolve in a solution only if it has a much stronger attraction to itself than to the solution.

Activity

Comment Stream