Solutions
This kind… 
Section 15.1
Forming Solutions
Objectives
1. To understand the process of dissolving
2. To learn why certain substances dissolve in water
3. To learn qualitative terms describing the
concentration of a solution
4. To understand the factors that affect how fast a solid
dissolves
Section 15.1
Forming Solutions
What is a solution?
 Solution – homogeneous mixture
 Solvent – substance present in largest amount
 Solutes – other substances in the solution
 Aqueous solution – solution with water as the
solvent
Section 15.1
Forming Solutions
Original State
of Solute
State of
Solvent
Air, natural gas Gas
Gas
Gas
Antifreeze in
water
Liquid
Liquid
Liquid
Brass
Solid
Solid
Solid
Carbonated
water (soda)
Liquid
Gas
Liquid
Seawater,
sugar solution
Liquid
Solid
liquid
Example
State of
Solution
Section 15.1
Forming Solutions
A. Solubility – Ionic Substances
 Ionic substances breakup into individual cations and
anions.
Section 15.1
Forming Solutions
A. Solubility of Ionic Substances
 Polar water molecules interact with the positive and
negative ions of a salt.
Section 15.1
Forming Solutions
Solubility of Polar
Substances
 Ethanol is soluble in water because of the polar OH bond.
Polar ethanol
Molecule 
 Polar
water
molecule
Section 15.1
Forming Solutions
A. Solubility – Polar Substances
 Why is solid sugar soluble in water?
 Polar substances are hydrophilic.
Polar OH
bonds in
sugar
molecule
Section 15.1
Forming Solutions
A. Solubility – Substances Insoluble in Water
 Nonpolar oil does not interact with polar water 
nonpolar substances are hydrophobic.
 Water-water hydrogen bonds keep the water from
mixing with the nonpolar molecules.
Section 15.1
Forming Solutions
A. Solubility – How Substances Dissolve
 A “hole” must be made in the water structure
for each solute particle.
 The lost water-water interactions must be
replaced by water-solute interactions.
 “like dissolves like” – polar solutes dissolve
in polar solvents, nonpolar solutes dissolve in
nonpolar solvents
Section 15.1
Forming Solutions
What kind of bear is hydrophilic?
A Polar Bear! 
Section 15.1
Forming Solutions
Solution Composition:
Concentration
• Amounts of substances can vary in different solutions.
– Concentration - amount of solute in relation to solvent
– Qualitative measures of concentration
• concentrated – relatively large amount of solute
• dilute – relatively small amount of solute
Section 15.1
Forming Solutions
Solution Composition: Concentration
Which solution is more concentrated?
B
Section 15.1
Forming Solutions
Solution Composition: Concentration
Which solution is more concentrated?
Neither
Section 15.1
Forming Solutions
Solution Composition:
How much solute can you dissolve in the solvent?
The solubility of a solute is limited.
 Saturated solution – contains as much
solute as will dissolve at that temperature
 Unsaturated solution – has not reached
the limit of solute that will dissolve at
that temperature
Section 15.1
Forming Solutions
Interpreting Solubility Curves
At 20oC, a solution
with less than 38g
NaCl in 100g water
would be
unsaturated.
At 40oC, about 38g NaCl
can be dissolved in 100g
water. The solution will
then be saturated.
How much Ba(NO3)2 can
be dissolved in 100g
water at 80oC?
Section 15.1
Forming Solutions
B. Solution Composition: An Introduction
 Supersaturated solution – occurs when a
solution is saturated at an elevated
temperature and then allowed to cool but
all of the solid remains dissolved
• Contains more dissolved solid than a
saturated solution at that temperature
• Unstable – adding a crystal causes
precipitation
Section 15.1
Forming Solutions
Making a Supersaturated Solution
At 20oC, a solution
containing ~19g Na2SO4
dissolved in it would be
saturated.
To dissolve more solute,
the temperature has to
be increased.
Ex.: At 20oC, a solution
containing more than
19g Na2SO4 dissolved in
it would be
supersaturated.
If we dissolve more
solute at a higher
temperature, then cool
the solution slowly so the
extra solute stays
dissolved in it, the
solution will be
supersaturated.
Section 15.1
Forming Solutions
Supersaturated Solution
YouTube Video
Section 15.1
Forming Solutions
Factors Affecting the Rate of Dissolving
Increasing the number of collisions between solute and solvent
particles increases the rate (speed) at which a solid dissolves.
Three factors that speed up dissolving:
– Increasing Surface area – dissolving occurs at the surface  the
greater the surface area exposed to solvent, the faster the
dissolving process
Ex.: A sugar cube will dissolve faster if it is ground to small
crystals, increasing the total surface area.
– Stirring – removes newly dissolved particles from the surface of
the solid and continuously exposes the surface to fresh solvent.
– Increasing Temperature – higher temperatures cause molecules
to move more rapidly; in addition, most solids are more soluble
at higher temperatures*.
Ex.: More sugar will dissolve in hot water than in cold water.
*For gases dissolved in water, the opposite is true: the solubility of
gases in water typically decreases as the temperature increases.
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problems?
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SOLUTIONS! 