The Nature of Solutions

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• The Nature of Solutions

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What is a Solution?

• A solution is a homogeneous mixture in which
• The particles are extremely small
  (submicroscopic) and considered to be individual
  particles.
• The particles are evenly distribut-ed throughout
  the entire mixture, such that the amount of
  dissolved particles is the same no matter where
  in the solution a sample is collected. (sample is
  an aliquot)

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What is a Solution?

• The particles in a solution wont separate out of
  the mixture once the particles are dissolved
  they stay dissolved.
• If the dissolved particles are ionic in nature,
  the solution will conduct electricity the
  dissolved ions are called electrolytes. (neither
  pure water nor dissolved covalent compnds will
  conduct electricity)

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What is a Solution?
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What is a Solution?
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A Study in Solutions
A solution is composed of two phases, solute and
solvent. The phase of a soln into which the
particles of the mixture are dissolved is the
solvent phase. the phase that does the
dissolving There is usually a higher volume of
the solvent present The solvent is typically not
involved in a chem rxn.
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A Study in Solutions
The solute phase is the phase of the solution
that is dissolved The solute is dissolved into
the solvent. There is usually a lower volume of
the solute present in relation to the solvent. In
a chemical reaction its the solute that is
involved in the reaction.
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A Study in Solutions
There are several different types of
solutions Solid solutions most common solid
soln is metal alloys (brass, bronze,
carbon-steel, etc.)
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A Study in Solutions
Gaseous solutions most common gaseous soln is
air When two or more gases are mixed they
automatically form a solution (all gaseous
mixtures form solutions)
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A Study in Solutions
Liquid solns most common liquid soln are those
in which the solvent is water (AKA aqueous). The
solvent and the soln is in the liquid phase,
but the solute
can be a gas,
solid, or liquid.
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The Formation of a Soln
A solution is formed through a series of
steps. 1st the attractive forces between
solute-solute particles and solvent-solvent
particles must be broken Particles must be
separated Intermolecular forces are
broken Requires energy so its an endothermic
process
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The Formation of a Soln
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The Formation of a Soln
2nd new intermolecular forces of attraction are
formed between solute-solvent particles Solvent
particles completely surround the solute
particles New attractions formed which releases
energy, so it is an exothermic reaction
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The Formation of a Soln
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The Formation of a Soln
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Degrees of Saturation
You cant dissolve an unlimited amount of solute
into solution There are degrees to how much you
can dissolve, Known as degrees of
saturation When you have a soln that can still
hold more solute it is called unsaturated You can
still dissolve more solute in an unsaturated
solution
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Degrees of Saturation
When you have a soln that can not hold any more
solute, the solute is classified as saturated You
add more solute into a soln that is already
saturated, it collects at the bottom of the
flask. The solvent is too
full, to hold
anymore solute.
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Degrees of Saturation
When you have a soln that has more solute
dissolved than the solvent should be able to
hold, are called supersaturated soln. The extra
solute that is dissolved is forced into soln by
heating Supersaturated solutions are extremely
unstable Even 1 more crystal can cause all of the
extra solute to resolidify.
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Degrees of Saturation
In a supersaturated soln, the soln is very
unstable, and is just barely holding onto its
solute. A single crystal can cause it to revert
back to saturated.
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Knowing How Much Solute
Its important to know how much solute is
dissolved in a solution Need to know the amount
of reactant (solute) in a chem rxn. Need to know
how much drug is in the soln (solute) Need to
know the edible amount of the flavoring (solute)
Knowing how much is the same as the
concentration of the solute
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Knowing How Much Solute
The concentration of a solution is defined as how
much solute is dissolved in a given amount of
solvent. In chemistry, these concentrations are
recorded calculated in Mass Percent Percent by
Volume Molarity Dilution
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Molarity
One way concentration is measur-ed is by how many
moles of solute are dissolved per liter of
solvent.
Molarity is interpreted as there is a 5.00 molar
solution of saline, there are 5.00 moles of salt
dissolved in enough water for a volume of 1
liter.
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Molarity
Vinegar is a dilute soln of acetic acid. What is
the molarity of the soln produced when 2.08 moles
of acetic acid is dissolved in sufficient water
to prepare a soln with a vol of 1.50 L?
2.08 moles
Molarity (M)
1.39 M
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Molarity
How many moles of bromine are dissolved in a 0.50
L soln with a 0.0100 M soln of bromine in Water?
X moles
0.0100 M
0.005 mols of Br2
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Mass Percent

• Concentration expressed as a percent ratio of
  solute vs. solvent.
• Describes solutions in which a solid is dissolved
  in a liquid.

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Mass Percent

• Percent by mass mass of solute x 100
• mass of solution
• Mass can be measured in any unit.

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Dilution (Molarity)
The concentration of a solution can be less
concentrated by a process of dilution. In order
to dilute a solution, more solvent is added, and
is still measurable.
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Dilution (Molarity)
M1V1 M2V2
Formula used to calculate how much sample is
needed to acquire a particular concentration of
soln?
M1 is the conc of the orig sample V1 is the
vol from the orig sample M2 is the conc of
diluted sample V2 is the vol of the diluted
sample
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Dilution (Molarity)
How much concentrated 18 M sulfuric acid is
needed to prepare 250 ml of a 6.0 M solution?
(V1)
(6.0 M)
(18 M)
(250ml)
V1 83 ml
So if we were to extract 83 ml of the 18 M soln
and add 167 ml of water, we would end up with
250 ml of 6.0 M sulfuric acid.
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Solubility
Not all types of solute particles will dissolve
in a solvent. Those that do dissolve are
considered soluble Those that dont dissolve are
considered insoluble To determine if particles
soluble you can Follow the solubility rules Or
look at the solubility constant
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Solubility Rules
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Solubility
The solubility of a particle is dependent on the
chemical nature of the particle itself. In order
for a solute to dissolve in a solvent the
particles involved must be compatible. Solute
particles that are polar in nature dissolve in
polar solvents particles that are nonpolar in
nature dissolve in nonpolar solvents
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Polar Solvents
Remember that polarity is established in
molecules that are unsymmetrical and have bonds
composed of atoms with significant
electronegativity differences. Solvents that are
polar in nature dissolve solutes that are polar
and/or charged. The charges of both
particles attract each other
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Polar Solvents
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Polar Solvents
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Nonpolar Solvents
No permanent dipoles are formed in these
solvents These solvents dissolve nonpolar
particles, but are immiscible in polar
solvents Dissolve each other
simply because the intermolecular
forces are so weak
that they mix together
polar
nonpolar
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Like Dissolves Like
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Increasing Solubility
Increasing the temp of a soln. can increase the
solubility of solids Increasing the temp
increases the motion of the solute particles The
solute moves faster so more more of it comes into
contact with solvent Increasing the temp of a
soln decreases the solubility of gases Gases are
high enough in energy that they are loosely
dissolved
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Increasing Solubility
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Increasing Solubility
Increasing the pressure over a soln will increase
the solubility of a gas The higher the pressure
the higher the solubility The pressure prevents
the gas from escaping from the soln. Increasing
the pressure over a soln will not affect the
solubility of a solid
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Increasing Solubility
Increasing the surface area of the solute
increases the solubility solvation takes place at
the surface of a solid The smaller the solute
particle, the more overall surface area
av-ailable for solvation to take place. If the
solute particles are large, it will help to
grind them into a fine powder to increase solu-
bility
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Solubility