Transcript SOLUTIONS 19.2 Chapter Nineteen: Solutions 19.1 Water 19.2 Solutions 19.3 Acids, Bases, and pH.

SOLUTIONS 19.2
Chapter Nineteen: Solutions
19.1 Water
19.2 Solutions
19.3 Acids, Bases, and pH
Chapter 19.2 Learning Goals
Explain how solutions are formed.
Define solubility and interpret
solubility graphs.
Describe factors that affect the
concentration of solutions.
Compare and contrast solubility of
solid, liquid, and gaseous matter.
19.2 Water and solutions
A solution is a mixture
of two or more
substances that is
uniform at the
molecular level.
19.2 Water as a mixture
Muddy water not a
solution.
Muddy water is
heterogeneous
because it contains
larger particles of
soil or plant debris.
19.2 Water and solutions
Although we often think of
solutions as mixtures of
solids in liquids, solutions
exist in every phase; solid,
liquid, or gas.
Solutions of two or more
solids are called alloys.
Steel is an alloy (solution) of
iron and carbon.
19.2 Suspensions
In a mixture called a suspension the
particles can range widely in size.
Muddy water, a suspension, will settle
when it is left still for a period of time.
19.2 Colloids
Colloids are mixtures, and look like
solutions, but their particles are too
small to settle to the bottom of their
container over time.
Examples of colloids are mayonnaise,
egg whites, and gelatin.
19.2 Tyndall effect
Tyndall effect is
occurring if you
shine a flashlight
through a jar of
liquid and see the
light beam.
19.2 Types of mixtures
 How can you tell the difference
between a solution, a colloid and a
suspension?
First, try filtering it, then look for the Tyndall effect.
19.2 Water and solutions
A solution contains at least two
components: a solvent, and a solute.
The solvent is the part of a mixture
that is present in the greatest amount.
Which of these is
the solvent?
19.2 Water and solutions
When the solute particles are evenly
distributed throughout the solvent,
we say that the solute has dissolved.
19.2 Solubility
The term solubility
means the amount of
solute (if any) that can
be dissolved in a
volume of solvent.
Is there a limit for how much
seltzer (solute) can dissolve in
water (solvent)?
19.2 Solubility
Chalk and talc do not have solubility
values.
These substances are insoluble in water
because they do not dissolve in water.
19.2 Solubility
A solution is saturated
if it contains as much
solute as the solvent
can dissolve.
Any solute added in
excess of the
substance’s solubility
will not dissolve.
What will happen to any un-dissolved gas when
you unscrew the cap of seltzer water?
Solving Problems
Seawater is a solution of water, salt,
and other minerals.
How much salt can dissolve in 200 mL
of water at 25 °C?
1. Looking for:
 …grams of solute
2. Given
 … v = 200 mL; T = 25 C
Solving Problems
1. Looking for:
 …grams of solute
2. Given
 … v = 200 mL water; T = 25 C
3. Relationships:
 Solubility table for reference
 38 g of salts in 100 mL water at 25 °C
4. Solution
 …if there are 38 g salt/100 mL water, then
 “x” g/ 200 mL water
 = 76 g salts are need in 200 mL of water
19.2 Solubility
A solution is saturated if it
contains as much solute as the
solvent can hold.
An examples of a saturated
solution is air.
 Air can be saturated with water.
(We call it humidity!)
19.2 Solubility
For something to dissolve in water,
the water molecules need to break the
bonds between the solute molecules.
Water dissolves each substance
differently because the chemical bond
strengths between atoms found in
different solutes are not the same.
19.2 Solubility graphs
Solubility values for three solutes are
plotted in this temperature-solubility graph.
19.2 Concentration
In chemistry, it is
important to know
the exact
concentration of a
solution—that is the
exact amount of
solute dissolved in a
given amount of
solvent.
19.2 Concentration
Two other common ways of expressing the
concentration of a solution are molarity
and mass percent.
19.2 Concentration
Molarity is equal to the moles of solute
per liter of solution.
19.2 Concentration
The mass percent of a solution is
equal to the mass of the solute
divided by the total mass of the
solution multiplied by 100%.
Solving Problems
How many grams of salt (NaCl) do you
need to make 500 grams of a solution with
a mass percent of 5% salt? The formula
mass of NaCl is 58.4 g/mol.
What is the molarity of this solution?
1. Looking for:
 …grams of solute
2. Given
 … mass solvent = 500 g; concentration = 5%
 …formula mass = 58.4 g/mol
Solving Problems
3. Relationships:
 Mass percent = mass of solute
total mass of solution
 Molarity = moles of solution
liter of solution
x 100%
4. Solution
 … 5% = (mass of salt ÷ 500 g) × 100%
 …0.05 × 500 g = 25 g
 # of moles = 25 g
= .4 moles
58.4 g/mol
 Assume 1 L of solution = .4 moles/L = .4M
19.2 Equilibrium
When a solute like sugar is mixed with a
solvent like water, two processes are
actually going on continuously.
 Molecules of solute dissolve and go into solution.
 Molecules of solute come out of solution and
become “un-dissolved.”
When the rate of dissolving equals the rate
of coming out of solution, we say
equilibrium has been reached.
19.2 Equilibrium
When a solute like sugar is mixed with a
solvent like water, two processes are
actually going on continuously.
 Molecules of solute dissolve and go into solution.
 Molecules of solute come out of solution and
become “un-dissolved.”
When the rate of dissolving equals the rate
of coming out of solution, we say
equilibrium has been reached.
19.2 Equilibrium
When a solution is unsaturated its
concentration is lower than the
maximum solubility.
A supersaturated solution means
there is more dissolved solute than
the maximum solubility.
19.2 Solubility of gases in liquids
 Some solutions have
a gas as the solute.
 When you drink
carbonated soda, the
fizz comes from
dissolved carbon
dioxide gas (CO2).
19.2 Solubility of gases in liquids
When temperature increases, the
solubility of gases in liquid
decreases.
19.2 Solubility of gases in liquids
The variety and no. or organisms is
controlled somewhat by the
relationship between dissolved
oxygen and temperature.
19.2 Solubility of gases in liquids
 Oil and vinegar
salad dressing
separates because
oil is not soluble
in water.
Liquids that are
not soluble in
water may be
soluble in other
solvents.
19.2 Solubility rules
A set of solubility rules helps predict
when an ionic compound is soluble or
insoluble.
Investigation 19C
Solubility of CO2
Key Question:
How is the solubility of a gas affected by
temperature?