ii iii i c. johannesson the nature of solutions solutions
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II
III
I
C. Johannesson
The Nature of Solutions
SolutionsSolutions
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MixturesMixtures
Can be divided into two categories:• Heterogeneous (different throughout)
–Suspensions
–Colloids• Homogeneous (same throughout)
–Solutions
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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!)
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Types of MixturesTypes of Mixtures
Solutions, Colloids, and Suspensions (based on size of solute)
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SuspensionsSuspensions
Particles in a suspension settle out.Examples: oil and water, paint, mud in
water, flour in water
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ColloidsColloids
Particles in a colloid scatter light, but are usually not visible to the human eye.
Examples: Milk, fog, mayonaise, shaving cream, jelly, blood
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SolutionSolution
Particles in a solution are never visible, and do not scatter light.
Example: sugar and water
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Tyndall EffectTyndall Effect
Scattering of light by colloidal particles• Used to distinguish a colloid from a
solution
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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
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SolutionsSolutions
The solute dissolves in the solvent!
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SolutionsSolutions
Solute + Solvent =Solute + Solvent = SolutionSolution
This makes a solution!
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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
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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!
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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.
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Factors that Affect SolubilityFactors that Affect Solubility
Pressure• Affects the solubility of gases in liquids
*Gases dissolve better at higher pressures!
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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”
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Factors that Affect SolubilityFactors that Affect Solubility
NONPOLAR
NONPOLAR
POLAR
POLAR
““Like Dissolves Like”Like Dissolves Like”““Like Dissolves Like”Like Dissolves Like”
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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
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Types of SolutionsTypes of Solutions
SATURATED SOLUTION
no more solute dissolves
UNSATURATED SOLUTIONmore solute dissolves
SUPERSATURATED SOLUTION
becomes unstable, crystals form
concentration
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Solubility CurveSolubility Curve
Where they are on a solubility curve
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Factors affecting the RATE of dissolving
Factors affecting the RATE of dissolving
Temperature Heat it!Surface Area Crush it!Agitation Stir it!
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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
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Units of Concentration:Units of Concentration:
1. Percent by Mass
% = mass of solute x 100
mass of solute + solvent
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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?
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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?
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Units of Concentration:Units of Concentration:
2. Molarity
M = moles solute
Liters of solution
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Example -Example -
What is the molarity of a
solution composed of
5.85g KI dissolved in
0.125L of solution?
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ExampleExample
How many moles of solute are
present in 10.2 liters of a 3.5
Molar solution?
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Units of Concentration:Units of Concentration:
3. Molality
m = moles solute
kg of solvent
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Example -Example -
What is the molality of a solution composed of 2.55g of acetone (CH3)2CO, dissolved in 200.0g water?
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Example:Example:
If a 6.0 molal solution contains 7.19 moles of solute, what is the mass, in kg, of solvent?