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

SOLUTIONS
Chapter Nineteen: Solutions
19.1 Water
19.2 Solutions
19.3 Acids, Bases, and pH
Chapter 19.1 Learning Goals
Describe water in terms of its
polarity.
Discuss properties of water related
to hydrogen bonding.
Explain why water is a good solvent.
Investigation 19A
Solubility Curve of KNO3
Key Question:
What is a solubility curve?
19.1 Water
We live on a watery planet.
All life on Earth depends on
this combination of hydrogen
and oxygen atoms.
 What are the properties of
water that make it so valuable?
19.1 The shape of a water
molecule
When two hydrogen
atoms each share
one electron with an
oxygen atom, a
neutral molecule is
formed.
19.1 The shape of a water
molecule
Because negative
charges repel, the
electrons pairs around
the oxygen atom are
located where they are
the farthest apart.
This results in a
geometric shape called
a tetrahedron.
19.1 Water is a polar molecule
A water molecule
has a negative end
(pole) and a positive
end.
A molecule (like
water) with a charge
separation is called
a polar molecule.
19.1 Another polar molecule
Ammonia, NH3, is
another polar
molecule. With one
lone pair and three
bonding pairs of
electrons.
This gives the
ammonia molecule a
pyramid shape.
19.1 Water is a polar molecule
Methane, CH4, is a
nonpolar molecule.
Since there are no
lone pairs of
electrons, the
electrons are
shared equally
between atoms.
19.1 Hydrogen bonds
A hydrogen bond is a bond between
the hydrogen on one molecule to
another atom on another molecule.
Hydrogen bonds are relatively weak
so they constantly break and re-form.
19.1 Ice and hydrogen bonds
Frozen water (or ice)
has an organized
structure that
resembles a
honeycomb because
each water molecule
can form hydrogen
bonds with four
other water
molecules.
19.1 Properties of water
Water has a high
specific heat value
because of hydrogen
bonds.
In order for water to
boil, enough energy
must be added to
separate the
hydrogen bonds.
19.1 Plants and hydrogen bonds
 The attraction
between water
molecules helps
water travel from
roots to stems
and leaves.
19.1 Water as a solvent
Water dissolves
sodium chloride
(salt) to form a
solution of
sodium (+) and
chlorine (-) ions.
19.1 Water as a solvent
In general, like
dissolves like:
 water dissolves
polar substances
 non-polar solvents
dissolve non-polar
substances
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?
Chapter Nineteen: Solutions
19.1 Water
19.2 Solutions
19.3 Acids, Bases, and pH
Chapter 19.3 Learning Goals
Differentiate acids and bases.
Define pH.
Explain the significance of acids,
bases, and pH to living organisms
and the environment.
Investigation 19B
Acids, Bases, and pH
Key Question:
What is pH?
19.3 What are acids?
An acid is a compound that dissolves in
water to make a particular kind of solution.
Chemically, an acid is any substance that
produces hydronium ions (H3O+) when
dissolved in water.
19.3 What are acids?
Some properties of acids are:
1. Acids create the sour taste in
food, like lemons.
2. Acids react with metals to
produce hydrogen (H2) gas.
3. Acids change the color of blue
litmus paper to red.
4. Acids can be very corrosive,
destroying metals and burning
skin through chemical action.
19.3 Bases
A base is any substance that dissolves
in water and produces hydroxide ions
(OH-).
19.3 What are bases?
Some properties of bases are:
1. Bases create a bitter taste.
2. Bases have a slippery feel, like
soap.
3. Bases change the color of red
litmus paper to blue.
4. Bases can be very corrosive,
destroying metals and burning
skin through chemical action.
19.3 Acids and bases
One of the most important properties of
water is its ability to act as both a weak acid
or as a weak base.
In the presence of an acid, water acts as a
base.
In the presence of a base, water acts as an
acid.
19.3 The pH scale
The pH scale ranges from 0 to 14.
 Acids have a pH less than 7.
 A base has a pH greater than 7.
 Pure water has a pH equal to 7.
19.3 Determining pH
pH is an abbreviation
for “the power of
hydrogen”.
The pH for a solution
equals the negative of
the exponent of the
hydronium ion (H3O+)
concentration.
Solving Problems
A solution contains a hydronium ion
concentration of 10-4.5 M. What is the pH
value of the solution? Is this solution
acidic or basic?
1. Looking for:
 …pH and whether acid or base
2. Given:
 … H3O+ conc. = 10-4.5 M.
3. Relationships:
 …pH = neg exponent of H3O+ concentration
4. Solution:
 …pH = 4.5
19.3 pH in the environment
The pH of soil directly affects the
availability of nutrients for plants.
Blueberries grow
best in what pH
soil?
19.3 pH in the environment
The pH of water directly affects
aquatic life.
How are frogs and
amphibians
sensitive to pH
changes?
19.3 The pH scale
Red and blue litmus paper are pH
indicators that test for acids or bases.
19.3 Acids and bases in your body
Many reactions, such as the ones that
occur in your body, work best at specific
pH values.
19.3 pH and blood
The pH of your blood
is normally within the
range of 7.3–7.5.
Holding your breath
causes blood pH to
drop.
High blood pH can be
caused by
hyperventilating.
Are You Feeling a Little Sour?
By nature, our slightly
alkaline pH needs to remain
balanced. Yet what we eat
and drink changes our pH.
For example, if you eat a lot
of meat and no vegetables,
your pH becomes acidic.