Download Water, Water Everywhere!

Review
• What is the difference between a compound
and an element?
– Give an example of each.
• What is the difference between a covalent and
ionic bond?
• What are van der Waals forces?
Properties of Water
Section 2-2
Water!
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What is the chemical formula for water?
How much water covers the Earth?
How much of your body is water?
Is there water in food?
How long could you live without water?
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H2O
75%
60-70%
Yes!
3 days
Properties of Water
• Phases: Solid, Liquid, Gas
• Polarity
• Hydrogen bonds
– Adhesion
– Cohesion
• Making Mixtures
– Solutions
– Suspensions
• Making Acids and Bases
Water Density
• Ice is less dense than liquid water
• When water freezes air is trapped within the
frozen ice making the cube larger and less
dense
• Benefits:
– Fish and plant life can survive in liquid layers of
water under ice
PHASE CHANGES:
the closeness and speed of the compounds
Polarity
Hydrogen ends
become slightly
positive
• Water is polar
• Although the
compound is
neutral overall
there is a shift
of charge
within the
compound
The much larger atom, Oxygen,
pulls more on the shared eThis end of the compound becomes slightly
more negative.
Hydrogen Bonding
• Due to polarity, water compounds attract to
one another
• Slightly negative oxygen attracts slightly
positive hydrogen from another compound
• This attraction among water is COHESION.
• Water is also attracted to other materials.
This is ADHESION.
COHESION
Water compounds attract
To one anothercauses water to “bead”
ADHESION
Water compounds attract
To glass molecules
And form a meniscus
The greatest solvent on Earth!
• Water’s polarity allows it to break ionic bonds
of other compounds…creating free ions.
Mixtures
Two or more elements physically mixed together but
not chemically combined (not bonded)
1. SOLUTIONS- a solute is dissolved into a solvent
– Distributes evenly
– Ex: Koolaid, salt water
2. SUSPENSIONS- added substance does not dissolve
but breaks into small enough pieces that it remains
suspended in the water and does not settle out.
- Ex: blood
RECAP
• Why does ice float on a lake?
• Explain the polarity of water – how are the
charges distributed?
• What is the difference between adhesion and
cohesion?
• Explain the difference between a solution and
a suspension
Water Dissociation
• Water can break apart on its own into 2 charged ions
– Hydrogen ions and hydroxide ions
Acids and Bases
Water can react to form individual ions:
H2O
H+ + OH-
• In pure water this occurs naturally but the
amount of H+ is always = to the amount of
OH- so water remains neutral
pH scale: “the power of Hydrogen”
• Some solutions made with water become acidic or
basic. This is determined by the amount of H+
(hydrogen ions) in the solution
Acids
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pH range from 0 – 6.99
Any compound that forms H+ ions in solution
H+ ions > OH- ions
The closer to 0 the more acidic the solution
Examples: stomach acid, lemon juice
Bases (Alkaline)
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pH ranges from 7.01 to 14
Any compound that forms 0H- ions in solution
OH- ions > H+ ions
The closer to 14 the more basic the solution
Examples: lye, bleach, oven cleaner
ACID:Any compound that forms H+ ions in solution
BASE: Any cmpnd that forms 0H- ions in solution
pH and Living Things
• pH values in living cells are usually kept
between 6.5 and 7.5
– Optimal pH for chemical reactions to take place in
the body
– Any switch in pH could cause serious/fatal
problems
Buffers
• Weak acids or bases that can react with strong
acids or bases
• Used to regulate pH and prevent sharp sudden
changes in pH
• There are natural buffers in your blood that
keep the pH at 6.5 to7.5
RECAP
• What makes a solution acidic or basic?
• How is acidity measured?
• A solution with pH 8.5 is considered….