Transcript Properties of

Properties of
Solutions
Changes In State
A Review of Matter
• Types of matter
• Pure substances
– Elements – cannot be broken down by chemical
means
– Compounds – two or more elements combined in
definite proportions
• Mixtures
– Homogeneous – evenly mixed, uniform throughout
– Heterogeneous – unevenly mixed, varied composition
Increasing Surface Area
Increases Dissolution
What is a Solution?
• Homogeneous mixture of substances in the
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same state.
A solution may be;
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A solid n solid. Ex. Zn + Cu  brass (alloy)
Gas n gas. Ex. Air.
Liquid n liquid. Ex. alcohol + water
And, most familiar to you, a substance, usually a
solid, dissolved in water.Ex. NaCl + water.(sea water)
Components of a Solutions
• A solute is the substance being dissolved.
• The solvent is the substance that exists in
the greater amount, into which the solute
is mixed.
• Ex. In sea water, salt is the solute, while
water is the solvent.
• Water’s properties make it a universal
solvent.
The Secret To Waters Dissolving
Power is it’s Polarized Nature
The polar water molecules surround the solute molecules, forming H-bonds
and dipole attractions
Aqueous Solutions
• Solutions of a substance dissolved in
water are termed aqueous and are written
as follows;
• NaCl (s)  Na+ (aq) + Cl- (aq) (where
s = solid, aq = aqueous, and g = gas)
• The particles of a homogeneous aqueous
solution are very small, will not settle and
will pass through a filter.
Mixtures Can Be Separated
Properties of Mixtures
• Light will pass directly through a solution.
• The light beam will not be visible in the
body of the solution.
• Light will be scattered by the larger
particles of heterogeneous solutions.
• This is called the Tyndall Effect, after the
scientist who discovered it.
Colloids and Suspensions
Scatter Light. Solutions Do Not.
Summary of Solution Properties
• Aqueous solutions are homogeneous
mixtures
• They are clear and do not disperse light.
• Can have color (ex. CuSO4 is blue).
• Particles will not settle when left standing.
• Particles pass readily through a filter.
Solubility
• Ability of a substance to dissolve in
another substance.
• “Like dissolves like.”
– Polar molecules dissolve in polar substances
– Non-polar (lipids, oils) dissolve in non-polar.
• All materials do not dissolve in equal
concentrations.
Solubility
• Highly soluble materials are said to be soluble
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or miscible.
Materials that dissolve very little are said to be
insoluble or immiscible.
A material dissolves because the attraction of the
solvent molecules is greater than the attractive
force holding the solute molecules together.
Insoluble materials have a greater affinity for
their own molecules.
These last 2 points is why oil pools together in
water
Temperature and Pressure
• Solubility is relative to changing temperature.
• Generally, solubility increases with increasing
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temperature.
Pressure has NO EFFECT on the solubility of
solids and liquids (that compressibility thing
again) ONLY GASES.
Gases behave oppositely, they are more soluble
at higher pressure and lower temperature
(open a warm seltzer bottle and a cold one at
the same time).
Gas Mixtures React Opposite to
Liquids in Terms of Pressure and
Temperature
Solubility Graphs
• We can look at a graph of solubility curves
to determine how much solute can
dissolve in a specific quantity of solvent.
• We need to know;
– Which solute
– What temperature
• See reference tables F and G.
Table F
• Guidelines for solubility (Table F)
– Table F is broken down into Ionic compounds
that are soluble. Try learning the exceptions,
there are fewer and you’ll know the rules by
default.
• There are many Ionic compounds that are
insoluble and many exceptions (use the
table).
Table G
• Graph of solubility curves
• Broken down into;
– X axis = Temperature in Celsius
– Y axis = amount of solute per 100g H2O.
• How to read graph
– Trace given info, grams or °C, along curve of
X and Y axis to find desired data point for
given solute.
Saturation
• There is an upper limit to how much solute a
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given solvent can hold at a certain temperature.
When holding the maximum amount of solute the
solution is said to be saturated.
When a solution is saturated the addition of any
more solute will cause a precipitate to form.
Ex. Have you ever found un-dissolved substance
on the bottom of your coffee or ice tea?
Using Table G (solubility curves)
To Predict Solubility of Substances
• Find KNO3 (potassium nitrate) in table G.
• At approximately 32°C, 100 grams H20 can hold
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a maximum of ~50grams of KNO3. It is
saturated at this mass and temperature.
If the temperature was raised to 50°C, 100g of
solvent could hold up to ~83 grams of KNO3.
One could add an additional 33 grams of solute
to re-saturate the solution.
If you do not add more solute, the solution
would be called unsaturated.
Supersaturation
• This occurs when a solution is heated, saturated
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and then slowly cooled, creating a new
saturation point.
The solution maintains it’s homogeneous
appearance.
Supersaturated solutions are very unstable.
Addition of a single crystalline molecule will
cause the solution to form a precipitate.
Determining Saturation
• Visual inspection: Does the solution contain un•
dissolved particles?
Addition of more solid solute:
1. Does the solid fall to the bottom?
• Yes  solution is saturated
• No  solution is not saturated
2. Does a precipitate form (material comes out of
solution)?
• Yes  solution is supersaturated
• No  return to (1)
Concentration of Solutions
• Compositions of homogeneous mixtures can
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vary.
Two terms are commonly used;
– Dilute
– Concentrated
• The above terms are relative, that is, they are
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not very precise and tell little about how much
solute is present.
More precise terms are; molarity, % mass, %
volume & ppm (parts per million).
Molarity
• Molarity is the number of moles of solute
per liter of solution.
M = # mol solute
L solution
• Molarity can be used as a conversion
factor to find Volume and # of mols.
M (mol/L) x V (L) = # of mol
Percent by Mass
• Mass of a certain ingredient divided by the
total mass.
% Mass = Mass of part x 100
Mass of Whole
Parts Per Million
• PPM is used when very small amounts are
present.
• Generally used to report acceptable levels
of toxins, pollutants, poisons or other
trace amounts of substances.
PPM = grams of solute x 106
grams of solution
Dilution
• The process of preparing a less
concentrated solution from a more
concentrated one.
M1 V1 = M2 V2
• Where M1 and M2 equal the old and new
molarities and…
• V1 and V2 equal the old and new volumes.