Chapter 12 - Solutions

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Chapter 12 - Solutions

• Chapter 12 - Solutions

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Solutions, Paul G. Mezey
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Chapter 12 - Solutions
Pure substances
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Weve seen that the physical properties of a pure
substance are dependent on the strength of the
intermolecular forces between the molecules
Solutions and Osmosis, Paul G. Mezey
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Chapter 12 - Solutions
Solutions
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Solutions are mixtures of two or more pure
substances. The substance found in greater
amounts is usually referred to as the SOLVENT,
while all other substances in the solution are
considered to be the SOLUTE(S).
Solutions and Osmosis, Paul G. Mezey
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Chapter 12 - Solutions
Solutions
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Solutes and solvents only tend to mix (are
MISCIBLE) when the intermolecular forces of the
solvent and solute(s) are of similar
strengths. Like dissolves like
Solutions and Osmosis, Paul G. Mezey
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Chapter 12 - Solutions
Figure
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If molecules A and B have large differences in
intermolecular force strengths, then a molecule
of A will be sucked back into pure A instead
of mixing with pure B. Oil (London forces) and
water (hydrogen bonds) DONT MIX, and are said to
be IMMISCIBLE.
Solutions and Osmosis, Paul G. Mezey
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Chapter 12 - Solutions
Figure
If molecules A and B have similar intermolecular
force strengths, then a molecule of A can mix
with pure B. Alcohols (hydrogen bonds) and
water (hydrogen bonds) DO MIX!
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Solutions and Osmosis, Paul G. Mezey
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Chapter 12 - Solutions
Physical properties of solutions
Even though like dissolves like, the presence
of solute molecules in the solvent disrupts the
bulk solvent intermolecular forces to some
extent. This change in forces means that the
physical properties of solutions, like freezing
and boiling points, are slightly different than
those of the pure solvent.
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Solutions and Osmosis, Paul G. Mezey
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Chapter 12 - Solutions
Physical properties of solutions
The disruption of forces generally depends more
on the amount of solute (in terms of
concentration) rather than the chemical identity
of the solute. Such colligative properties of
solutions therefore depend on the concentration
of the solution while ignoring the identity of
the solute.
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Solutions and Osmosis, Paul G. Mezey
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Chapter 12 - Solutions
Dilution of solutions
If we take a solution and add pure solvent to it,
we expect dilution to occur. The solution and
solvent mix until a new solution of lower
concentration is made.
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Solutions and Osmosis, Paul G. Mezey
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Chapter 12 - Solutions
Dilution of solutions
If we instead take a solution and separate it
from pure solvent using a semipermeable
membrane that solute molecules cant pass
through, then we are controlling the mixing.
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Solutions and Osmosis, Paul G. Mezey
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Chapter 12 - Solutions
Osmosis
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Solutions and Osmosis, Paul G. Mezey
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Chapter 12 - Solutions
Osmosis
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Osmosis is the process where the solvent passes
through the semipermeable membrane driven by
the trend to EQUALIZE the solute concentration
on both sides of the membrane.
Solutions and Osmosis, Paul G. Mezey
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Chapter 12 - Solutions
Osmosis
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Solutions and Osmosis, Paul G. Mezey
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Chapter 12 - Solutions
Osmotic pressure
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Osmotic pressure is a colligative property of a
solution that is defined as the external
pressure that must be applied to a solution to
just stop the process of osmosis through the
membrane.
Solutions and Osmosis, Paul G. Mezey
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Chapter 12 - Solutions
Osmotic pressure
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Osmotic pressure P depends on the concentration
of the solution (M), the temperature (T) and the
gas constant (R). P MRT
Solutions and Osmosis, Paul G. Mezey
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Chapter 12 - Solutions
Osmotic pressure and molar mass
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• 1. Make a solution of a certain mass of solute
  in a given total volume.
• 2. Measure the osmotic pressure.
• 3. Calculate M from measured P and T.
• Use M and volume to calculate the
• moles of solute.
• 5. Use moles and mass of solute to calculate
  molar mass.

Solutions and Osmosis, Paul G. Mezey
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Chapter 12 - Solutions
Problem
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An aqueous solution of 21.6 mg of vasopressin
in 100.0 mL of solution has an osmotic pressure
at 25 ?C of 3.70 mmHg. What is the molar mass of
the hormone?
Solutions and Osmosis, Paul G. Mezey
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Chapter 12 - Solutions
Osmosis and biology
Cell walls are often semipermeable membranes that
allow water to pass through, but not many solute
molecules. Body fluids, like blood plasma, must
have concentrations that match those inside the
cell or osmosis might cause cells to shrink or
rupture.
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Solutions and Osmosis, Paul G. Mezey
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Chapter 12 - Solutions
Blood cells and osmosis
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Solutions and Osmosis, Paul G. Mezey
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Chapter 12 - Solutions
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Solutions and Osmosis, Paul G. Mezey
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Be Careful
Be Careful !

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Attention, Paul G. Mezey