Transcript The Chemistry of Water - Hatboro

The Chemistry of Water
The Chemistry of Water
H bond
Water is a polar
molecule.
Has both + & –
charges
Cohesion
1. When water molecules form
hydrogen bonds with other water
molecules.
Adhesion
•H2O molecules form hydrogen bonds
with other polar molecules.
•water climbs up fiber – ex. paper towel
Surface tension:
Adhesion & Cohesion working together
•A property of liquid
surfaces that causes the
surface layer to behave like
a thin elastic 'skin‘ & results
in a downward pulling
motion of water
molecules.
Capillary Action:
Adhesion & Cohesion working together
The upward pull
of water against
gravity from
plants roots to
the leaves.
The Chemistry of Water
1. H2O molecules form hydrogen
bonds with each other
2. + attracted to –
3. creates a ‘sticky’
molecule
Low Density of Ice
• Most (all?) substances are more
dense when they are solid
But not water…
•Ice floats!
–H bonds form a crystal
with loose structure
Ice floats…..
ice floats because hydrogen bonds hold water
molecules further apart in a solid than in a
liquid
Why is it so impt that ice floats?
•Oceans & lakes don’t freeze solid
if ice sank…
•eventually all ponds, lakes & even
ocean would freeze solid
•during summer, only upper few
inches would thaw
•surface ice insulates water below
allowing life to survive the winter
Temperature Moderation
•Organisms relay on heat of vaporization
to remove heat
Temperature Moderation
•H2O resists changes in temperature
–takes a lot to heat it up
–takes a lot to cool it down
•H2O moderates temperatures on
Earth
The Universal Solvent
•H2O is a good solvent due to its polarity
• polar H2O molecules surround + & –
ions
• solvents dissolve solutes creating
aqueous solutions
•Saltwater; which is solute?
which is solvent?
The universal solvent
Questions
1. What causes hydrogen bonds to form between
polar molecules?
(A) The atoms of polar molecules give up
electrons to hydrogen atoms.
(B) Polar molecules have partially charged
regions that attract other polar molecules.
(C) The hydrogen atom in water molecules
becomes negatively charged.
(D) Hydrogen atoms in water molecules attract
each other with positive charges.
Questions
2. Which of the following properties
of water is not caused by hydrogen
bonding?
(A) pH
(B) cohesion
(C) adhesion
(D) surface tension
Questions
3. What term describes the sugar in a
glass of lemonade?
(A) solvent
(B) solution
(C) solute
(D) protein
Questions
4. What is the relationship between
hydrogen bonds and ionic bonds?
5. What determines whether a
compound will dissolve in water?
6. How do polar molecules form
hydrogen bonds?
Properties of Water Review
Ability to dissolve other substances
Creates surface tension
Exhibits capillary action
Low density of ice
Temperature moderation
• Goldfish hibernate at the bottom of a pond in the
winter.
• Humans cannot have too high of a fever or the
chemical reactions in their bodies will stop.
• Land near large bodies of water stay warmer
longer in the fall then land away from large
bodies of water.
Properties of Water Review
• Goldfish hibernate at the bottom of a pond in the
winter.
• Humans cannot have too high of a fever or the
chemical reactions in their bodies will stop.
• Land near large bodies of water stay warmer
longer in the fall then land away from large
bodies of water.