Transcript Shape Group Methods

Chapter 12 - Solutions
Chapter 12 - Solutions
.
Solutions,
Paul G. Mezey
Chapter 12 - Solutions
Pure substances
.We’ve 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
Chapter 12 - Solutions
Solutions
.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
Chapter 12 - Solutions
Solutions
. 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
Chapter 12 - Solutions
Figure
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) DON’T MIX,
and are said to be IMMISCIBLE.
Solutions and Osmosis,
Paul G. Mezey
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!
Solutions and Osmosis,
Paul G. Mezey
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.
Solutions and Osmosis,
Paul G. Mezey
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.
Solutions and Osmosis,
Paul G. Mezey
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.
Solutions and Osmosis,
Paul G. Mezey
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 can’t pass through,
then we are “controlling the mixing.”
Solutions and Osmosis,
Paul G. Mezey
Chapter 12 - Solutions
Osmosis
.
Solutions and Osmosis,
Paul G. Mezey
Chapter 12 - Solutions
Osmosis
.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
Chapter 12 - Solutions
Osmosis
.
Solutions and Osmosis,
Paul G. Mezey
Chapter 12 - Solutions
Osmotic pressure
. 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
Chapter 12 - Solutions
Osmotic pressure
. 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
Chapter 12 - Solutions
Osmotic pressure and molar mass
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.
4. 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
Chapter 12 - Solutions
Problem
.
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
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.
Solutions and Osmosis,
Paul G. Mezey
Chapter 12 - Solutions
Blood cells and osmosis
.
Normal blood cell
in isotonic (same
concentration)
solution.
Collapsed blood cell
in hypertonic (more
concentrated)
solution.
No osmosis.
Water leaves the
cell during osmosis.
Bloated blood cell
in hypotonic (less
concentrated)
solution.
Water enters the
cell during osmosis.
Solutions and Osmosis,
Paul G. Mezey
Chapter 12 - Solutions
.
Solutions and Osmosis,
Paul G. Mezey
Be Careful
.
Attention,
Paul G. Mezey