Solutions!
Classification of Matter
Matter
Pure
Mixtures
Substances
Homogeneous Heterogeneous
Elements Compounds
Mixtures Mixtures
Heterogeneous Mixtures
• See visibly different regions
– Granite
– Dirt
– Cereals
– Oil & Vinegar
• See a boundary
– Ice cube in water
Homogeneous Mixtures
• Particles very small – on atomic scale
– Can’t see particles
– Can’t sort particles
– Can’t get trapped by filter
– Can’t scatter light
• Particles are evenly distributed
• Particles do not separate
CuSO4(aq)
source source
Which is a solution & how do you know?
Solution
• Homogeneous mixture of 2 or
more substances in a single
physical state (phase)
Parts of a Solution
• Solute = dissolved substance
• Solvent = dispersing medium
Identify the solute
and solvent in each
picture
Solute = ? Solvent = ?
Hints to identify solute & solvent
• Solute: changes phase
= substance you have less of
• Solvent: maintains phase
= substance have the most of
Aqueous Solutions
• Water is
solvent
• Transition
metals form
brightly
colored
solutions
Solutions occur in all 3 phases!
Solute Solvent Example
Gas Gas Air
Liquid Gas Water Vapor in Air
Solid Gas Mothballs
Gas Liquid Seltzer Water
Liquid Liquid Antifreeze in radiator
Solid Liquid Salt water
Gas Solid H2 in Pd metal
Liquid Solid Fillings: Hg in Ag
Solid Solid Alloys: Brass, etc.
Gas dissolved in a solid
CO2 in and out of water
Bubbles mean it’s a mixture not a solution!
Alloys
Alloys
Soluble
Soluble – capable of being dissolved
A substance that dissolves in
another substance is soluble
in that substance
Insoluble
A substance that does not
dissolve in another substance
Amounts that can dissolve
• Solubility = maximum amount of
substance that will dissolve in given
amount of another substance
• LIMITS to amounts of most liquid/solid
solutes that will dissolve in given solvent
• Temperature and pressure affect solubility
Factors that affect the rate of dissolving
• Rate of dissolving is different from
amount that will dissolve!
• Rate is how fast
–factors influence rate of dissolving:
• Temperature
• Stirring or Agitation
• Surface Area of Solute
• Amount of solute already dissolved
Dissolving
• Dissolving is physical change
• All physical & chemical changes
are accompanied by changes in
energy
Equations for Dissolving
C6H12O6(s) + H2O(l) C6H12O6(l)
NaCl(s)+H2O(l) Na+1(aq) + Cl-1(aq)
source
Covalent substances dissolve to produce
molecules in solution
Ionic substances dissolve to produce
ions in solution
Solvation
• Interaction between solvent molecules and
solute particles
– Solute particles are surrounded by solvent
particles in the dissolving process
• Solute particles may be ions, polar molecules,
or nonpolar molecules
• Solvent molecules may be polar or nonpolar
Hydration
Specific name for solvent-solute
interaction when solvent is water
Hydration of
chloride ion
Also called:
molecule-ion
interaction
Molecule-ion interaction
Solute-solvent interaction
must be greater than:
interaction between
solute particles
for dissolving to occur
Solvation in different systems.
Solubility
• Amount solute that will dissolve in specific
solvent at given TEMPERATURE and
PRESSURE
• Amount can be determined experimentally
• Units:
grams solute per 100 grams solvent
Solubility Curves of Selected Solids
Solubility traces
for most but not
all solids have
(+)’ve slopes;
The hotter the
solvent, the
more solute
dissolves
Solubility Curves of Selected Gases
Solubility
traces for all
gases have
(–)’ve slopes
Why do fish like cold water?
Why do you see
bubbles form on
the side of the
beaker as the
water warms up?
(Note: it’s not hot
enough to boil)
Vocabulary Interlude
• Miscible: two liquids that mix
together in any amounts
– Water and ethanol are miscible in all
proportions
• Immiscible: Liquids that will not mix
– Oil and water are immiscible
Oil & H2O are immiscible
Types of Solutions
Matter
Pure Substances Mixtures
Homogeneous Heterogeneous
Elements Compounds Mixtures =
Mixtures
Solutions
Conduct current
Nonconductor
Electricity
• What do you need to conduct
electricity?
Mobile, charged particles!!!!
Vocabulary Interlude
• Electrolyte:
• substance that dissolves in water to form
solution that conducts electricity
• ions in the solution
• Nonelectrolyte:
• substance that dissolves in water to form
solution that does not conduct electricity
• neutral molecules in solution
Electrolyte vs. Nonelectrolyte
Which solution conducts a current?
Dilute vs. Concentrated
Tells relative amount of solute in solvent
• Concentrated
–large amounts of solute
• Dilute
–small amounts of solute
Which solution is
most dilute?
The most
concentrated?
How do you
know?
The stronger the color, the more
concentrated the solution
Which solution is
more concentrated?
More dilute?
What can you say
about the # of solute
particles in pictures
b and c?
It’s the same!
Unsaturated Solution
Less solute than maximum amount
that will dissolve at that temperature
and pressure
Saturated Solution
• No more solute will dissolve at
that temperature & pressure
• Solubility = amount of solute
required to form a saturated
solution
The solution is saturated when the solute
stops dissolving
Dynamic Equilibrium = Saturated Solution
Microscopic level:
Rate of dissolving =
Rate of
recrystallization
Macroscopic level:
No apparent change
Supersaturated Solution
• Contains more solute than
saturated solution
–VERY unstable
–have to be clever to make them up
(need to use heat)
Testing for saturation:
Toss a crystal of solute into
solution and see what happens
3 possible results:
• Crystal dissolves: Unsaturated solution
• Crystal sinks to bottom of solution:
Saturated solution
• Bam! Suddenly have lots of solid solute in
beaker: Supersaturated solution
What kind of solution was this?
How do terms saturated, unsaturated &
supersaturated fit in with the solubility curves?
• Saturated solutions have maximum solute that will
dissolve at given temperature
– Points on traces represent saturated solutions
• All points above a trace represent supersaturated
solutions of that solute
• All points below a trace represent unsaturated
solutions of that solute
Characterize points
A A, B, C, D with respect
B to the KNO3 trace
using the terms
dilute & concentrated,
saturated, unsaturated,
or supersaturated
C A,C = concentrated &
D supersaturated
B,D = dilute &
unsaturated
Summary of Dissolving
• Occurs at surface of solid
• Involves interaction between solute
and solvent
• Interaction is called “solvation”
• If water is solvent, interaction is called
“hydration”
• Involves changes in energy
Solubility Information
• Often presented in graphs
• Graph show number of grams of substance that
can be dissolved in water between 0oC and
100oC
• Trace represents a saturated solution
– space above each trace represents supersaturated
solutions
– space below each trace represents unsaturated
solutions
Solubility Graphs
• Traces: have positive or negative slopes
• Most solids have positive slope
– the hotter the water, the more solute dissolves
• All gases have negative slope
– the hotter the water, the less gas dissolves
– The colder the water, the more gas dissolves