A solution is a mixture of two components, a solute and a solvent. The solute is the substance being dissolved and is less abundant, while the solvent does the dissolving and is more abundant. Solutions can become more or less concentrated depending on how much solute is dissolved. Molarity is used to describe concentration and is calculated as moles of solute per liter of solution. Dilutions add water to more concentrated solutions to make them weaker. Mixtures are classified based on particle size and whether they exhibit the Tyndall effect.

1. Solutions
IB Chemistry: Chapter 1 Section 1.5

2. What parts make up a solution?
 Solution
is a mixture of two components.

1. Solute: less abundant component, the substance being
dissolved

2. Solvent: more abundant component, the dissolver

Solutions in water are called aqueous (aq).

3. Concentration

As more and more solute gets dissolved, the solution becomes
more concentrated.

When the solvent can no longer dissolve any more solute, it is
saturated. (If less solute is dissolved, unsaturated.)

Solution can dissolve more solute than usual under particular
circumstances – supersaturated.

4. Molarity
 Molarity
is a term we use to describe concentration.
= mol/dm3, Molarity = moles (n) of solute dissolved
in 1 dm3 of solution.
M
is the molarity of 2.98g of NaCO3 in 500cm3 of
solution?
 What

5. Dilutions

Sometimes, we need a diluted solution for a particular
procedure.

In order to dilute, you add water to a more concentrated
solution.

The equation we use to determine how much concentrated
solution we need is:
 M1V1=M2V2

6. Types of Mixtures
 Classified
by:
 Size of the particles
 Whether they exhibit the Tyndall effect

7. Types of Mixtures
 Solution:
 Particles
are evenly distributed and do not
separate on standing
 No Tyndall Effect
 Example: food coloring and water mixture

8. Solution Example
Notice how you
cannot see a
distinction between
solute and solvent. It
is the same
throughout the
solution.

9. Types of Mixtures
 Suspensions:
 Particles
are not evenly distributed. Particles
are suspended but will eventually settle into
layers
 Exhibits Tyndall Effect
 Examples: Dirt and water mixture

10. Suspensions
The larger particles in
a suspension settle
out over time.
Particles are only
physically combined.

11. Types of Mixtures
 Colloids:
 Particles
are not evenly distributed. Particles are
suspended but will eventually settle into layers
 Exhibits Tyndall Effect
 Examples: milk

12. Colloids
Looks like a solution to the
naked eye. Particles are
suspended. The particle size
is the “in betweener”, larger
than a solutions’ particles
but smaller than a
suspensions’ particles.

13. What is this “Tyndall effect”?
 Light
scattering by particles.
 Found
in colloids and suspensions, but not
solutions.

14. Tyndall Effect

15. Hydrates
 Hydrates
are ionic compounds that have water molecules
absorbed into the crystal lattice.
 Hydrates
are still solid, just have certain amounts of water
attached to the ions.
 An
example of a hydrate is Copper (II) Sulfate pentahydrate:
 CuSO4 ● 5H2O

16. Hydrates

An example of a hydrate is:
 CuSO4  5H2O
 This means that for every 1 unit of copper sulfate, there
are 5 units of water.
 Or, for every 1 mole of copper sulfate there are 5 moles of
water.

Solve for the molar mass. (The dot does not mean
multiply, just add the mass of water to mass of copper
sulfate.)

17. Properties of Solutions:
Dissociation
 When
 If
a solute dissolves, the solute molecule is
surrounded by water molecules.
the solute is ionic, than the ions separate and are
surrounded by water molecules.
 Example:
NaCl  Na+ + Cl-

18. Model of NaCl dissolving in water
Na+
ClNa+
ClNa+
Cl-
Na+
Cl-
Cl-
Na+
Na+

19. Dissociation Continued

Because of this, ionic substances have more of an effect on the boiling point
and freezing point than a covalent bond (something that is not ionic).




C6H12O6 (s)  C6H12O6 (aq)
NaCl(s)  Na+ (aq) + Cl-(aq)
CaCl2 (s)  Ca2+ (aq) + 2Cl-(aq)
(1 particle being dissolved, not ionic)
(2 particles being dissolved, ionic)
(3 particles being dissolved, ionic)
CaCl2 will have the largest effect (higher melting/boiling pts) and glucose
the least effect (lower melting/boiling pts).

20. Ability to Conduct Electricity

If ions are present in solution, it will conduct eletricity……all
ionic substances will conduct electricity when dissolved.
 Ex: Tap water, salt water

Solutes that conduct electricity when dissolved are called
electrolytes.

21. Electrolytes
 Importance
of electrolytes:
 The movement of calcium ions allows muscles to
contract and relax
 Presence
of sodium and potassium ions allow your
nerve cells to respond to stimuli.

22. STRONG vs. weak Electrolytes

Strength depends on number of ions in solution

More ions = stronger electrolyte, Fewer ions = weaker
electrolyte

For strong electrolytes, increasing concentration increases conductivity

Weak electrolytes, increasing concentration does not effect conductivity

23. Think about it!!!
 For
strong electrolytes, increasing concentration
increases conductivity
 Weak
electrolytes, increasing concentration does not
effect conductivity
WHY????

24. Colligative Properties

1. Boiling point of the solvent elevates

2. Freezing point is lowered
Vapor pressure is lowered, fewer molecules of solvent are
escaping to the gas phase when a solute is present. The solvent
molecules cannot escape because they are “busy” keeping the
solute dissolved.


25. Salting the Roads!
 Rock
salt (CaCl2) is used to keep the roads from
freezing in the winter. Ever wonder why that
happens????