Unit 4: Solutions
8.2 : Characteristics of
Solutions
What is a Solution?
• A homogeneous mixture of two or more substances
• Solutions can be
• solids (ex. An alloy is a solution of two or more metals)
• liquids (ex. Apple juice)
• gases (ex. Air)
Solution Terminology
In a solution (ie: sugar water), there is:
Solute  the substance that is in lesser quantity
the substance that dissolves in the solvent
 ie: sugar
Solvent  the substance that is in greater quantity
 What dissolves the solute
 ie: water
Solution Terminology
Concentrated Solution  a solution with a relatively large
quantity of solute compared to the volume of the solution
Dilute Solution  a solution with a relatively small quantity
of solute compared to the volume of solution
8.3: The Dissolving Process
The Dissolving of Ionic Compounds
• In order for ionic compounds to dissolve, the bonds
within it must be broken.
• How can an ionic compound, like NaCl, dissolve in water
at room temperature? By:
• Hydration: the process where ions are surrounded
by water molecules, and
• Dissociation: the separation of ions that occurs when
ionic compounds dissolve
NaCl(s) 
Na + (aq) + Cl - (aq)
3K3PO4(s)  3 K+
(aq) + PO4 (aq)
The Dissolving of Molecular Compounds
• Molecular compounds vary with how easily they dissolve in
water
• Depends on polarity and hydrogen bonds!
• Miscible  liquids that mix in all proportions (ex. Ethanol
and water)
• Immiscible  liquids that do not mix (ex. Oil and water)
Dissolving Rules
• RULE for dissolving: *Like Dissolves Like*
• Solutes dissolve in solvents of similar polarity
If solute is Ionic or polar covalent, it:
• dissolves in polar solvents
• because the solute-solvent attractions are strong, so the
solutes are able to break the solvent HYDROGEN bonds
to form new bonds.
Dissolving Rules
If the solute is non-polar, it:
• does not dissolve in polar solvents
• because the solute-solvent attractions are weak
compared to the attractions between solvent
molecules. Solutes cannot break solvent hydrogen
bonds.
Dissolving Rules
Examples:
• Does KCl dissolve in H2O?
• YES: ionic compounds
• always dissolve in water
• Does CO2 dissolve in H2O?
• NO: CO2 is non-polar, and water is polar.
• Does CO2 dissolve in CH4?
• YES: both are non-polar (like dissolves like!)
Surfactant
• A compound that can reduce the surface tension of a
solvent
• Allow polar solvents to mix with non-polar liquids
(water)
(oil)
• Soaps and detergents are surfactants!!
• When you are washing your greasy hands, does only
water work to remove the grease?
• NO! You need soap!
Surfactant
•
•
•
•
A surfactant has a non polar “tail” and a polar “head”
The non-polar tail attaches to the non-polar grease or oil
The polar head attaches the polar water molecules
Now the water can connect to and remove the
grease/oil!
8.2: pg 381 # 1 – 3, 8
8.3: pg 384 # 1; pg 389 # 2, 3, 6, 8, 12, 14