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Chapter Five: Solutions
Lesson One: Introduction to Solutions
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Classifying Solutions
A homogeneous mixture consisting of a solute and a solvent.
The substance present in the highest quantity is the solvent.
An aqueous solution (aq) has water as the solvent. March 16, 2015
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Types of Solutions: Solutes and Solvents Can Exist in Any Phase
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Did you know??
I
Y
I
F
FY Milk is not actually a solution! I Although it appears to be a homogenous Y
F mixture milk is a "colloid" -­‐ a heterogenous mixture. The particles are I so small that you cannot see them Y
F
without a magnifying glass or a microscope. I
FY
Other examples -­‐ smoke & marshmallows
I
FY
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Solutions in Water
Water is often required for chemical reactions to occur. When solutes are dissolved in water, they are mobile within the solvent, so they can collide with other chemicals more readily. March 16, 2015
Dissolving and Forces of Attraction
What happens when something dissolves?
1. The force between particles in the solute , c
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n
o
break (endothermic process) io , Dip
on d
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or L H-­‐Bo
2. Some of the intermolecular forces in the solvent break (endothermic process) 3. The attraction between the particles of the solute and the particles of solvent result in the formation of new intermolecular bonds (exothermic process) March 16, 2015
Process of Dissolving
The overall process of dissolving can be exothermic or endothermic depending on the energy involved in each step for a particular substance
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If dissolving is:
exothermic
-­‐ the temperature of the solution will increase and the solute dissolves
FYI
endothermic
-­‐ the temperature of the solution will decrease and the solute dissolves
EXothermic = EXiting
ENdothermic = ENtering
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Insoluble substances...
An insoluble substance will not dissolve because the particles in the solute are more attracted to each other than they are to the solvent. March 16, 2015
Electrolytes and Non-­‐Electrolytes
Electrolytes are substances that form solutions that conduct electricity
-­‐ ions are present in the solution
Non-­‐electrolytes are substances that form solutions that don't conduct electricity
-­‐ no ions are present in the solution
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An Interesting Aside
These are electrolyte imbalances, showing the importance of electrolytes in your bodily functions. Salt ions are in high
concentration in the body. Electrolytes are important in the body because they are what your cells use to maintain voltages
across cell membranes to carry electrical impulses and nerve transmissions. In exercise, electrolytes (specifically sodium and
potassium) are lost through sweat and it is imperative that they be replaced. Electrolyte replacement is also crucial when one
has chronic vomiting or diarrhea.
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Arrhenius' Idea
-­‐ Arrhenius studied solutions and their ability to conduct electricity
-­‐ Concluded that ionic solids do not conduct electricity, but their solutions do. -­‐ He proposed that the ionic solids dissociated when they dissolved March 16, 2015
Dissociation
The separation of ions that occurs when an ionic compound dissolves in water
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Dissociation Equations
A dissociation equation shows the process of dissociation
Example
NaCl(s) -­‐-­‐ in water -­‐-­‐> CaBr2(s) -­‐-­‐ in water -­‐-­‐> March 16, 2015
Write a dissociation equation for the following ionic compounds:
FeSO4(s)
(NH4)2S2O3(s)
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NiCl
2(s)
chromium (III) cyanide
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molecular compounds will dissolve depending on the polarity of the solute and solvent
(like dissolves like)
if a molecular compound dissolves it does not dissociate
Example:
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http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::100%::100%::/sites/dl/free/
0072512644/117354/07_Strong_Weak_Nonelectrolytes.swf::Strong%20Electrolytes,%20Weak
%20Electrolytes,%20and%20Nonelectrolytes
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Practice
Read Textbook p. 166-­‐175
Questions: p. 168 -­‐ # 1, 2
p. 170 -­‐ # 3-­‐5
p. 175 -­‐ # 7, 8
p. 175 -­‐ Review -­‐ # 1-­‐7
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