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C. Johannesson
The Nature of Solutions
SolutionsSolutions
C. Johannesson
MixturesMixtures
Can be divided into two categories:• Heterogeneous (different throughout)
–Suspensions
–Colloids• Homogeneous (same throughout)
–Solutions
C. Johannesson
MixturesMixtures
Can also be classified according to the size of their solute.• Solution < 1nm• Colloid 1-1000 nm• Suspension >1000nm
FYI: 1nm = 1 x 10-9 m = 0.000000001m (in other words…really small!)
C. Johannesson
Types of MixturesTypes of Mixtures
Solutions, Colloids, and Suspensions (based on size of solute)
C. Johannesson
SuspensionsSuspensions
Particles in a suspension settle out.Examples: oil and water, paint, mud in
water, flour in water
C. Johannesson
ColloidsColloids
Particles in a colloid scatter light, but are usually not visible to the human eye.
Examples: Milk, fog, mayonaise, shaving cream, jelly, blood
C. Johannesson
SolutionSolution
Particles in a solution are never visible, and do not scatter light.
Example: sugar and water
C. Johannesson
Tyndall EffectTyndall Effect
Scattering of light by colloidal particles• Used to distinguish a colloid from a
solution
C. Johannesson
DefinitionsDefinitions
Solution - Solution - homogeneous mixture made by dissolving one substance (solute) into another substance (solvent).
Solvent Solvent – substance that dissolves the solute
Solute Solute - substance being dissolved
C. Johannesson
SolutionsSolutions
The solute dissolves in the solvent!
C. Johannesson
SolutionsSolutions
Solute + Solvent =Solute + Solvent = SolutionSolution
This makes a solution!
C. Johannesson
SolubilitySolubility
Solubility is the measure of how “dissolvable” a substance is.
(maximum grams of solute that will dissolve in
100 g of solvent at a given temperature) Some substance will not dissolve
insoluble Some will dissolve
Soluble
C. Johannesson
Factors that Affect SolubilityFactors that Affect Solubility
Temperature
• solids, liquids increased temperature leads to an increase in solubility
• gases increase in temperature leads to a decrease in solubility
What does this mean?
• Solids dissolve better at higher temperatures while gases dissolve better at lower temperatures!
C. Johannesson
Solubility CurveSolubility Curve
shows the dependence of solubility on temperature
As temperature increases, the solubility of most solids increases and the solubility of gases decreases.
C. Johannesson
Factors that Affect SolubilityFactors that Affect Solubility
Pressure• Affects the solubility of gases in liquids
*Gases dissolve better at higher pressures!
C. Johannesson
Factors that Affect SolubilityFactors that Affect Solubility
Nature of the Solute
• Water is called the universal solvent because it is a polar molecule (making it easy to dissolve most things).
• Polar solutes dissolve in polar solvents.
• Non-polar solutes dissolve in non-polar solvents.
• “Like dissolves Like”
C. Johannesson
Factors that Affect SolubilityFactors that Affect Solubility
NONPOLAR
NONPOLAR
POLAR
POLAR
““Like Dissolves Like”Like Dissolves Like”““Like Dissolves Like”Like Dissolves Like”
C. Johannesson
Types of SolutionsTypes of Solutions
When you dissolve one substance into another, a limited amount of solute can be dissolved in a given amount of solvent.
Three types of Solutions can be made:• Unsaturated• Saturated• Supersaturated
C. Johannesson
Types of SolutionsTypes of Solutions
SATURATED SOLUTION
no more solute dissolves
UNSATURATED SOLUTIONmore solute dissolves
SUPERSATURATED SOLUTION
becomes unstable, crystals form
concentration
C. Johannesson
Solubility CurveSolubility Curve
Where they are on a solubility curve
C. Johannesson
Factors affecting the RATE of dissolving
Factors affecting the RATE of dissolving
Temperature Heat it!Surface Area Crush it!Agitation Stir it!
C. Johannesson
ElectrolytesElectrolytes
StrongElectrolyte
Non-Electrolyte
All of it Ionizes
Bright Light
- +
salt
- +
sugar
None of it ionizes
No Light
- +
acetic acid
WeakElectrolyte
Some of it ionizes
Weak Light
C. Johannesson
Units of Concentration:Units of Concentration:
1. Percent by Mass
% = mass of solute x 100
mass of solute + solvent
C. Johannesson
Example:Example:
A solution of NaCl is prepared
by dissolving 5.0g of salt in
550.5g of water. What is the
percent by mass concentration
of this solution?
C. Johannesson
Example:Example:
A solution of sugar water is
prepared by dissolving 124.8
grams of glucose in 1775 grams
of water. What is the percent by
mass concentration of this
solution?
C. Johannesson
Units of Concentration:Units of Concentration:
2. Molarity
M = moles solute
Liters of solution
C. Johannesson
Example -Example -
What is the molarity of a
solution composed of
5.85g KI dissolved in
0.125L of solution?
C. Johannesson
ExampleExample
How many moles of solute are
present in 10.2 liters of a 3.5
Molar solution?
C. Johannesson
Units of Concentration:Units of Concentration:
3. Molality
m = moles solute
kg of solvent
C. Johannesson
Example -Example -
What is the molality of a solution composed of 2.55g of acetone (CH3)2CO, dissolved in 200.0g water?
C. Johannesson
Example:Example:
If a 6.0 molal solution contains 7.19 moles of solute, what is the mass, in kg, of solvent?