SOLUTIONS
Chapter 13
What is a solution?
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In chemistry, a solution is a homogenous mixture
composed of two or more substances. In such a mixture,
a solute is dissolved in another substance, known as a
solvent. A common example is a solid, such as salt or
sugar, dissolved in water,a liquid.
A mixture is a substance made by combining two or
more different materials in such a way that no chemical
reaction occurs. The objects do not bond together in a
mixture. A mixture can usually be separated back into
its original components. Some examples of Mixtures are
oil, ocean water and soil.
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A suspension is a heterogenous fluid containing
solid particles that are sufficiently large for
sedimentation.
A colloid is a homogeneous solution with
intermediate particle size between a solution and a
suspension.
What is concentration?
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Solvent: The substance in which the solute dissolves
to make the solution.
Solute: The substance dissolved in a solution.
Aqueous: Describes a solution in which the solvent is
water.
Concentration: The quantity of solute in a specific
quantity of solvent or solution.
Molarity: A concentration unit, expressed in moles of
solute per liter of solution.
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Molarity(M) = moles of solute/liters of
solution=mol/L
Class Practice
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What is the molarity of a potassium chloride
solution that has a volume of 400 ml and contains
85 g of KCl?
Sodium thiosulfate, Na2S2O3, is used as a fixer
when developing photographic film. What is the
mass in grams of Na2S2O3 needed to make 100ml
of a 0.250M solution?
Home work
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Page 475 Practice problems do all odd #.
Separating mixtures
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There are many ways to separate mixtures into their
components.
filtering
distillation
chromatography
Magnetic
separation
Different ways of separating
mixture
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1 A magnet can be used to separate IRON from SAND.
How it works: The magnet sticks to the iron but not to the sand.
3. Filtering (filtration) can be used to separate a solid (or suspension)
from a liquid.
How it works: The liquid (and anything dissolved in the liquid) passes
through holes in the filter paper but the solid particles are too big and get
stuck.
Example: Filtration would be used to separate the dirt from some salty
water.
4. Evaporation can be used to separate a dissolved SOLUTE from a
SOLUTION
Example: Evaporation would be used to obtain some pure salt from salty
water.
How it works: When salty water is warmed the water evaporates leaving
behind crystals of salt.
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Distillation is a method of separating chemical
substances based on differences in their volatilities in a
boiling liquid mixture. Example: Used to separate crude
oil into more fractions for specific uses such as transport,
power generation and heating.
Chromatography is a physical method of separation in
which the components to be separated are distributed
between two phases, one which is the stationary
(stationary phase) while the other (the mobile phase)
moves in a definite direction..
Gas Solubility
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Gases can dissolve in liquids: Gases may dissolve in
liquids, for example, carbon dioxide or oxygen in
water.
Gas solubility depends on pressure: A soda bottle can
be considered to be saturated since there is some soda
above the liquid level and some is in the liquid itself.In
an unopened soda bottle there is much higher partial
pressure of CO2 in the neck of the bottle, above the
liquid than there is in the air outside the bottle. Due to
this difference in the pressure the CO2 dissolves in the
liquid.
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Gas solubility decreases with increasing
temperature: After the soda bottle is opened the
soda is allowed to warm, the soda forms fewer
bubbles and tastes flat.
Liquids and miscibilities
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Miscible: Indicates liquids that will dissolve in each
other.
Immiscible: Indicates liquids that will not dissolve
appreciably in each other example oil and water.
Polarity of the solute and solvent
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Polar solvents dissolve polar compounds, and non
polar solvents dissolve non polar compounds
example when a sugar cube having polar sucrose
molecules is dissolved in water a polar solvent.
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Hydrogen bonding : High solubility is expected
when hydrogen bonds form between solute and
solvent molecules.
Two compounds that are both polar or both non
polar are likely to be miscible.
Two compounds that can form hydrogen bonds with
each other are likely to be miscible.
Solubility principles at work
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Dry cleaners use solubility principles to remove
stains. Commonly used dry cleaning solvent is
tetrachloro ethylene C 2Cl4.
Vitamin C dissolves in water. Some sources of
vitamin C are,
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Vitamin A dissolves in oils and fats. Vitamin A
affects vision because the human body uses it to
make a pigment called visual purple, one of the
vital light sensitive molecule in the retina.
Conductivity in Solutions
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Conductivity is a measure of water’s ability to
conduct electrical current. Measurements of
conductivity provide a general indication of water
quality.
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Electrical conductivity is a measure of a material's
ability to conduct an electric current. When an
electrical potential difference is placed across a
conductor, its movable charges flow, giving rise to
an electric current. The conductivity σ is defined as
the ratio of the current density to the electric field
strength :
Electrolytes
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What are electrolytes?
Electrolytes are substances that become ions in
solution and acquire the capacity to conduct
electricity.
Non electrolyte is a substance that does not
dissociate into ions and so in solution it is a
nonconductor of electricity.
Non electrolyte
in solution
Weak electrolyte
Strong electrolyte
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Tap water conducts electricity:
You should avoid water when you are using electricity.
Unlike distilled water that does not conduct enough
electricity to light a bulb in the conductivity apparatus
tap water contains various ions from dissolved
minerals. Water sources like water from a well has
more concentration of salts than the surface water
such as lakes and rivers.
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While swimming in the pool, get out of the pool
if a thunderstorm strikes. Chlorinated water
conducts electricity.
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Dissociation: A process in which a compound
separates into fragments, such as simpler
molecules,atoms,radicals or ions.
Hydration: The process by which water molecules
surround each ion as it moves into solution.
Factors affecting solubility
 Temperature:The
solubility of a given solute in a given
solvent often depends on temperature. For around 95%
of solid solutes, the solubility increases with
temperature, but gaseous solutes exhibit more complex
behavior. As the temperature is raised gases usually
become less soluble in water, but more soluble in
organic solvents.
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Pressure:Henry’s Law states that the solubility of a gas is
directly proportional to the pressure of that gas, which may be
written as p=kc
where k is a constant.
Polarity: "Like dissolves like" This indicates that a solute will
dissolve best in a solvent that has a similar polarity to itself.
For example, a very polar (hydrophilic) solute such as urea is
highly soluble in highly polar water, less soluble in fairly polar
methanol, and practically insoluble in non-polar solvents such
as benzene.
Colligative properties
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Colligative properties of solutions are properties that depend
upon the concentration of solute molecules or ions, but not upon
the identity of the solute. Colligative properties include
1. freezing point depression: the difference between the
freezing point of a pure solvent and that of a solution.
2. boiling point elevation:the difference between the boiling
point of a solution and that of the pure solvent.
3.vapor pressure lowering, and osmotic pressure.
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The concentration of the solute affects freezing and
boiling point changes: The more particles there are
the greater the freezing point depression and the
boiling point elevation. Based on the number of
moles of solute particles produced, 1 mole of
sodium chloride is expected to be twice as effective
dissolved in water as 1 mol of sucrose,
C₁₂H₂₂O₁₁(s)H₂O- C₁₂H₂₂O₁₁ (aq)
NaCl(s)-H₂ONa+(aq)+Cl-(aq)
Emulsions
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An emulsion is a mixture of two immiscible
substances. One substance is dispersed in the other
Examples of emulsions include butter and
margarine, espresso, mayonnaise, the photosensitive side of photographic film, and cutting fluid
for metal working. In butter and margarine, a
continuous liquid phase surrounds droplets of water
(water-in-oil emulsion). Emulsification is the process
by which emulsions are prepared.
Surfactant
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What is soap?: A sodium or potassium salt of a long
chain fatty acid. If the skin has accumulated oil dirt
and bacteria then to remove this one must first
emulsify the oil by scrubbing then stabilize it with an
emulsifier such as soap.
Only then can the soap and oily dirt emulsion be
rinsed away from the skin.
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The soap ion dissolves the oil, forming a tiny sphere
called a micelle, while the other end on the outside
of the micelle dissolves in the surrounding water. The
oil droplet stays suspended in the water and can be
easily washed away. The characteristic property of
a surfactant is its ability to form a layer between
two dissimilar phases.
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Soap forms micelle which is the bubble.A thin film of
water is coated on both surfaces by soap molecules.
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Hard water destroys soap’s surfactant abilities.
Detergents outperform soaps in hard water.
Homework
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Page 504
Term review all
Test prep all
Q.9 b
Q 10 all
Q.24 and 32 all