# Chapter 15 � Solutions

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```					Chapter 15 – Solutions
Goals for Chapter 15
• Understand solutions
• Calculations of various ways to express
concentrations of components in solutions
• Understand Colligative properties:
– Boiling point elevation
– Freezing point depression
– Osmotic pressure

9 equations for this Chapter

Some images taken from Lemay – 10 edition
What are solutions?
A solution is a homogenous mixture of two or more substances

The solute is(are) the substance(s) present in the smaller
amount(s)

The solvent is the substance present in the larger amount

Type of solutions

Concentrated and dilute – know the difference.
The solution process – NaCl in H2O
The intermolecular forces between solute and solvent particles
must be strong enough to compete with those between solute
particles and those between solvent particles.

Name three factors that affect rate of dissolving.
Surface Area
Stirring                  Explain
Temperature
Conductors?
An electrolyte is a substance that, when dissolved in water,
results in a solution that can conduct electricity.

A nonelectrolyte is a substance that, when dissolved, results
in a solution that does not conduct electricity.

nonelectrolyte      weak electrolyte     strong electrolyte

Can you name examples of each?
What dissolves in What?
Two substances with similar intermolecular forces are likely to
be soluble in each other.

•     non-polar molecules are soluble in non-polar solvents
CCl4 in C6H6
•     polar molecules are soluble in polar solvents
C2H5OH in H2O
•     ionic compounds are more soluble in polar solvents
NaCl in H2O or NH3 (l)

“like dissolves like”

Understand the difference between chemical reactions and solution formation
Temperature
Generally, the solubility of solid solutes in liquid
solvents increases with increasing temperature. Do
you know why?
Temperature
• The opposite is true of gases:
 Carbonated soft drinks are more “bubbly” if stored in
the refrigerator.
 Warm lakes have less O2 dissolved in them than cool
lakes.
Fractional crystallization is the separation of a mixture of substances
into pure components on the basis of their differing solubilities.

Suppose you have 90 g KNO3
contaminated with 10 g NaCl.

Fractional crystallization:
1.   Dissolve sample in 100 mL of
water at ~600C
2.   Cool solution to 00C
3.   All NaCl will stay in solution (s
= 34.2g/100g)
4.   78 g of PURE KNO3 will
precipitate (s = 12 g/100g). 90
g – 12 g = 78 g
OK, what does that big M stand for
on the bottle in front of the room?
We need ways to discuss how much solute a given volume of
solution contains – quantitatively – this is not cooking school.

You will know how to calculate:

% by mass, mole fraction, ppm, Molarity, and molality, and dilution

The concentration of a solution is the amount of solute
present in a given quantity of solvent or solution.
Expression of Concentration – the Equations – know these

Percent by Mass                     Molarity
mass solute                 moles solute
% mass                   100     M 

Mole Fraction (c)                     molality
nsolute                  moles solute
cA                        m
ntotal                   kgssolvent
Sum fractions = 1             dilutions
ppm (parts per million)               M 1V1  M 2V2
mass solute                You should be an expert at

ppm                 10 6       writing formulas and calculating
moles – also, density comes into
mass solution              playas well (molality).
Let’s try some
•   A solution containing equal masses of glycerol (C3H8O3) and water has
a density of 1.1 g/ml. Calculate M, m, and mole fraction of glycerol.

5.97 M, 10.9 m, 0.163
•   A solution is made by dissolving 13.5 grams of glucose in 0.100 kg of
water. What is the mass percentage of solute?

11.9%
•   A 2.5 g sample of ground water was found to contain 5.4 mg of Zn2+.
What is the concentration in ppm?

2.2 ppm

•   How would you prepare 60.0 mL of 0.2 M HNO3 from a stock solution of
4.00 M HNO3?

3 mL of acid + 57 mL of water = 60 mL

Worksheets and WebAssign
Titrations
In a titration a solution of accurately known concentration is
concentration until the chemical reaction between the two
solutions is complete.
Equivalence point – the point at which the reaction is
complete
Indicator – substance that changes color at (or near)
the equivalence point

to unknown acid
UNTIL
the indicator
changes color
What volume of a 1.420 M NaOH solution is required to titrate
25.00 mL of a 4.50 M H2SO4 solution?

H2SO4(aq) + 2NaOH(aq)                   2H2O(aq) + Na2SO4(aq)

4.50 mol H2SO4            2 mol NaOH
25.00 mL x                     x
1000 mL soln             1 mol H2SO4

1000 ml soln
x                    = 158 mL
1.420 mol NaOH

Is this type of calculation really anything new?
Colligative Properties of Solutions
Colligative properties are properties that depend only on the
number of solute particles in solution and not on the nature of
the solute particles.
1. Boiling Point Elevation

ΔTb = iKbm

2. Freezing Point Depression              Why m and not M?

ΔTf = iKfm

3. Osmotic Pressure

p = iMRT
K values are tabular information found in your book
But why?
• Non-volatile solutes reduce the ability of the
surface solvent molecules to escape the liquid.
Therefore, vapor pressure is lowered.
• The amount of vapor pressure lowering
depends on the amount (number of particles) of
solute.
K values and normal bp and fp
values
The result – altered PCD
Colligative Properties
and i
Colligative properties depend on the number of particles
dissolved – so - solutions of electrolytes (which
dissociate in solution) should show greater changes
than those of nonelectrolytes.
The van’t Hoff Factor

Tf = iKfm

We will be using the limiting values in our calculations – determine
how many ions are produced by dissolution of the compound
Why not whole numbers for i?
• One mole of NaCl in water does not really give rise to
two moles of ions.
• Some Na+ and Cl− reassociate for a short time, so the
true concentration of particles is somewhat less than two
times the concentration of NaCl. What determines the
“somewhat”?

Worksheets and WebAssign
Osmosis
•   Some substances form semipermeable membranes, allowing
some smaller particles to pass through, but blocking other larger
particles.
•   In biological systems, most semipermeable membranes allow
water to pass through, but solutes are not free to do so.
•   In osmosis, there is net movement of solvent from the area of
higher solvent concentration (lower solute concentration) to the
are of lower solvent concentration (higher solute concentration).
Osmotic Pressure
• The pressure required to stop osmosis,
known as osmotic pressure, p, is

n
p = i(         )RT = iMRT
V
where M is the molarity of the solution

If the osmotic pressure is the same on both sides
of a membrane (the concentrations of solute are
the same), the solutions are isotonic.
Osmosis in Cells
• If the solute concentration
outside the cell is greater than
that inside the cell, the solution
is hypertonic.
• Water will flow out of the cell,
and crenation results.
• If the solute concentration
outside the cell is less than that
inside the cell, the solution is
hypotonic.
• Water will flow into the cell, and
hemolysis results.

IV fluids better be….

Colloids in Biological Systems
• Sodium stearate is one example of
such a molecule.

• These molecules can aid in the
emulsification of fats and oils in
aqueous solutions.
What’s Next? Chapter 12 – Heat in
Chemical Reactions
• Please R&O Chapter 12 – print off
all materials listed for this chapter.

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