Transcript Chapter 7 Notes

Chapter 7: Solutions

A solution is a
homogeneous
mixture that
consists of the
solute and the
solvent.
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Liquid Solutions

The solute can NOT be
separated from the solvent
by filtration.
 It can ONLY be separated
by evaporation of the
solvent.
 Solute particles are not
visible, but can produce a
colored solution.
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Types of Solutions
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Water as a Solvent


Water is one of the most common (and important!)
solvents as it can dissolve a variety of substances.
Water is highly polar (Ch. 4) with hydrogen bonding
intermolecular forces.
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Water as a Solvent

Water dissolves most ionic compounds.
 When NaCl dissolves in water, sodium ions at
the surface are attracted to the oxygen atoms
in water and the chloride ions at the surface
are attracted to the hydrogen atoms in water.
 Each ion is surrounded by six water
molecules referred to as a hydration sphere.
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Water
as a
Solvent
Video
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Water as a Solvent

Water also dissolves highly polar molecules
like formaldehyde (CH2O) and molecules with
hydrogen bonding like methanol.
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CCl4 – a Non-polar solvent

Carbon
tetrachloride is a
tetrahedral
molecule, but
each C-Cl bond
pulls in an equal
and opposite
direction making it
non-polar.
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CCl4 – a Non-polar solvent
Only non-polar solutes will dissolve in
CCl4.
 Ex) I2, C10H8, and CS2.
 What do these have in common?

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Summary of Solubility

“Like dissolves like”
Water
Ni(NO3)2
dissolves in
polar layer
Distinct
boundary
layer
CCl4
I2 dissolves in
non-polar layer
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Learning Check

Would the following substances be
soluble in Water or CCl4?
– Glyceraldehyde (a simple sugar)
– Hexane
– CaCl2
– Br2
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Electrolytes
Pure water is a
poor conductor
of electricity.
 When ions are
present, though,
water becomes
an excellent
conductor.

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Strong, Weak, and Non-electrolytes

Strong electrolytes
are substances that
completely dissociate
into ions when in
water.
 Most ionic
compounds are
strong electrolytes.
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Strong, Weak, and Non-electrolytes

Weak electrolytes
are substances that
partially dissociate
into ions when in
water.
 Weak acids and
weak bases are
weak electrolytes.
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Strong, Weak, and Non-electrolytes

Non-electrolytes are
substances that
dissolve in water, but
produce no ions.
 These are molecular
compounds like the
alcohols and sugars.
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Formation of Ions

Split the following into ions.
– NaCl
– CaCl2
– Na2SO4
– Al(NO3)3
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Equivalent (Eq)





An equivalent is the amount of an electrolyte
that produces one mole of charge.
Does NOT depend on the type of charge
(positive or negative), just the magnitude of
the charge.
1 mole Na+ = 1 Eq
1 mole Ca+2 = 2 Eq
1 mole PO4-3 = 3 Eq
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Equivalent

Determine the number of equivalents
present in:
– 0.25 moles of Mg+2
– 0.23g of Na+1
– 4.50g of CO3-2

Convert Eq to grams
– A solution contains 0.23 Equivalents of
HPO4-2. What mass is present?
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Electrolytes in Body Fluids

In replacement solutions for body fluids, the
electrolytes are given in milliequivalents per
liter (mEq/L).
Ringer’s Solution (Saline)
Na+

147 mEq/L Cl−
K+
4 mEq/L
Ca2+
4 mEq/L
155 mEq/L
Note that the mEq/L of cations must equal the
mEq/L of anions.
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Solubility
Solubility is the maximum amount of
solvent that can be dissolved in a
specific amount of solvent.
 Usually expressed as the mass of
solute per 100. grams of solvent.

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Unsaturated Solution

When a solution
could dissolve
more of the
solute, it is said to
be unsaturated.
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Saturated Solution

Contains the
maximum amount
of solute allowed.
If you added more
solid, it will not
dissolve.
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Solubility and Temperature
Most solid solutes
will increase in
solubility with an
increase in the
temperature.
 Can produce a
super-saturated
solution!

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Sodium Acetate

Start with 160g of NaC2H3O2 in 100mL of
water at 20oC.
 Begin to warm to 100oC.
 Then cool – no solid forms!
Temperature
20o C
60o C
100o C
Solubility Limit
46g / 100mL
139g / 100mL
170g / 100mL
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Sodium Acetate
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Solubility and Temperature

The solubility of a
gas in a liquid
decreases with an
increase in
temperature.
 Fish need >5ppm
to thrive.
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Concentration of Solutions
The quantity of solute in a solution can
be defined as a percentage.
 Used commonly in the health field.
 Mass / Mass Percentage (m/m or w/w).

= mass of solute (g) x 100
mass of solution (g)
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Concentration of Solution
Volume / Volume Percentage (v/v).
= volume of solute (mL) x 100
volume of solution (mL)
 Mass / Volume Percentage (m/v or w/v).
= mass of solute (g)
x 100
volume of solution (mL)

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Using a Percentage
A percentage can be written as a
fraction and then used as a conversion
factor.
 Thus, a 5.0% NaCl (m/m) can be written
as:
5.0 g of NaCl
100.g of solution

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Molarity
Chemists use this method for
concentration.
 M = moles of solute / Liters of solution.
 Problems may involve mass that must
be converted to moles.

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Dilution
Stock solutions are often diluted to use
in a laboratory.
 The moles of solute remain the same!
 C1 x V1 = C2 x V2
 C’s can be either a percentage or a
molarity.
 V’s can be either milliliters or liters, but
both must be the same unit.

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Solution Stoichiometry
Molarity and volumes can be used to
calculate quantities for an aqueous
reaction.
 Remember that M = Moles / Liters.
 Will require a mole-to-mole conversion
in second step from balanced reaction.

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Solutions

A solution:
– is transparent (may be colored).
– contains tiny solute particles, which are not
visible.
– does not settle out over time.
– can not be filtered.
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Colloids
A colloid contains larger solute particles
that causes the “Tyndall effect.”
 A collloid:

– will be opaque.
– can not be filtered.
– does not settle out over time.
– can be separated by a semi-permeable
membrane.
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Types of Colloids

Aerosol = a liquid or solid in a gas.

Foam = a gas in a liquid or solid.

Emulsion = a liquid or solid in a liquid.

Sol = a liquid or solid in a solid.
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Suspensions
A suspension contains very large solute
particles.
 A suspension:

– is opaque.
– will settle out over time.
– can be filtered.
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Comparison
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Learning Check

Classify as a solution, colloid, or
suspension.
– The CaCO3 made a few weeks ago in the
lab (Chemical Reaction exercise).
– Mixing a Crystal lightTR packet with water.
– Orange juice (no pulp).
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Osmosis

When a semi-permeable membrane
separates two solutions, only the solvent
molecules can move across the barrier.
 If two solutions of different concentrations are
placed on either side of the barrier, then the
solvent will flow from the lower solute side to
the higher solute side.
 To prevent this, an external pressure would
be needed to stop the net flow.
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Osmosis
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Osmotic Pressure
The pressure necessary to prevent the
net flow is proportional to the molarity of
the solution.
 Higher molarity = Higher osmotic
pressure.

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Learning Check

A semipermeable membrane separates a
10% sucrose solution A from a 5% sucrose
solution B. If sucrose is a colloid, fill in the
blanks in the statements below.
1. Solution ____ has the greater osmotic
pressure.
2. Water initially flows from ___ into ___.
3. The level of solution ____will be lower.
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Importance of Osmosis
Our cells have semi-permeable
membranes to contain the cell materials
inside.
 Our blood plasma has an osmotic
pressure equal to that of our red blood
cells.
 Any external fluid administered like an
I.V. must be isotonic.

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Isotonic Solutions

A saline solution
(NaCl) will have a
concentration of
0.90% (m/v).
 A glucose (aka
dextrose) will have a
concentration of
5.0% (m/v).
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Hypotonic Solutions

If a solution of
lower
concentration
comes into contact
with a red blood
cell, that solution
is said to be
hypotonic.
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Hypertonic Solutions

If a solution of
higher
concentration
comes into
contact with a red
blood cell, that
solution is said to
be hypertonic.
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Learning Check

When placed in each of the following, indicate
if a red blood cell will
1) not change, 2) hemolyze, or 3) crenate.
A.____ 5% glucose solution
B.____ 1% glucose solution
C.____ 0.5% NaCl solution
D.____ 2% NaCl solution
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