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
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.
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
Generally, the solubility of solid solutes in liquid
solvents increases with increasing temperature. Do
you know why?
• The opposite is true of gases:
Carbonated soft drinks are more “bubbly” if stored in
Warm lakes have less O2 dissolved in them than cool
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.
1. Dissolve sample in 100 mL of
water at ~600C
2. Cool solution to 00C
3. All NaCl will stay in solution (s
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
mass solution literssolution
Mole Fraction (c) molality
nsolute moles solute
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?
• A 2.5 g sample of ground water was found to contain 5.4 mg of Zn2+.
What is the concentration in 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
In a titration a solution of accurately known concentration is
added gradually added to another solution of unknown
concentration until the chemical reaction between the two
solutions is complete.
Equivalence point – the point at which the reaction is
Indicator – substance that changes color at (or near)
the equivalence point
Slowly add base
to unknown acid
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
• 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
K values and normal bp and fp
The result – altered PCD
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
Worksheets and WebAssign
• Some substances form semipermeable membranes, allowing
some smaller particles to pass through, but blocking other larger
• 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).
• The pressure required to stop osmosis,
known as osmotic pressure, p, is
p = i( )RT = iMRT
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
• 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
• Water will flow into the cell, and
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
What’s Next? Chapter 12 – Heat in
• Please R&O Chapter 12 – print off
all materials listed for this chapter.