Transcript UNIT SEVEN: Earth’s Water  Chapter 21 Water and Solutions  Chapter 22 Water Systems  Chapter 23 How Water Shapes the Land.

UNIT SEVEN: Earth’s Water
 Chapter 21 Water and Solutions
 Chapter 22 Water Systems
 Chapter 23 How Water Shapes the
Land
Chapter Twenty-One: Water and
Solutions
 21.1 Water
 21.2 Solutions
 21.3 Acids, Bases, and pH
Chapter 21.2 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.
Investigation 21B
Solubility Curve of KNO3
 Key Question:
What is a solubility curve?
21.2 Water and solutions
 A solution is a mixture
of two or more
substances that is
homogeneous at the
molecular level.
 Homogeneous means
the particles are evenly
distributed.
21.2 Water as a mixture
 Muddy water is heterogeneous because it
contains larger particles of soil or plant
debris.
21.2 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.
21.2 Tyndall effect
 Tyndall effect is
occurring if you shine a
flashlight through a jar
of liquid and see the
light beam.
 This distinguishes a
colloid from a solution.
21.2 Suspensions
 In a mixture called a
suspension the particles
can range widely in size.
 Muddy water, will settle
when it is left still for a
period of time.
21.2 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.
21.2 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?
21.2 Water and solutions
 When the solute particles are evenly
distributed throughout the solvent, we
say that the solute has dissolved.
21.2 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)?
21.2 Solubility
 Chalk and talc do not have solubility values.
 These substances are insoluble in water
because they do not dissolve in water.
21.2 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
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
3. Relationships:

Solubility table for reference

35.9 g of salts in 100 mL water at 25 °C
4. Solution

…if there are 35.9 g salt/100 mL water, then

“x” g/ 200 mL water

= 71.8 g salts are need in 200 mL of water
21.2 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!)
21.2 Solubility graphs
 Solubility values for three solutes are plotted in
this temperature-solubility graph.
21.2 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.
21.2 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.
21.2 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.
21.2 Solutions of gases and liquids

Some solutions have
a gas as the solute.

In carbonated soda,
the fizz comes from
dissolved carbon
dioxide gas (CO2).
21.2 Solutions of gases and liquids
 When temperature increases, the
solubility of gases in liquid decreases.
21.2 Solutions of gases and liquids
 The variety and no. or organisms is
controlled somewhat by the
relationship between dissolved oxygen
and temperature.
21.2 Solutions of gases and liquids
 The concentration of dissolved oxygen
in water is important for fish and
aquatic life.
21.2 Solutions of gases and liquids
 Oil and vinegar salad
dressing separates
because oil is not
soluble in vinegar
(mostly water).
 Liquids that are not
soluble in water may
be soluble in other
solvents.
21.2 Solubility rules
 A set of solubility rules helps predict
when an ionic compound is soluble or
insoluble.