1. Water
The Molecule That Supports All Of Life
AP Biology 2007-2008
2. The Chemistry Of Water
Water is a polar molecule
The atoms of water are held together by
polar covalent bonds
Who wins?
Oxygen(-)?
Hydrogen(+)?
AP Biology
3. Noodle time!
Do hydrogen bonds hold oxygen
and hydrogen together IN water?
Pink – Yes
Purple – No
Yellow – I’m not sure
AP Biology
4. Noodle time!
What kind of bonds do hold the
hydrogen atoms to the oxygen
atom in H2O?
Pink – Non-polar covalent
Purple – Hydrogen
Yellow – Ionic
Green – Covalent
AP Biology
5. The Chemistry Of Water
Molecules of water are held together by
Hydrogen bonds
H+ of one water molecule attracted to O- of
another water molecule
AP Biology
6. The Properties Of Water (Super Powers)
1. Cohesion & Adhesion
2. Good Solvent
3. Low Density As A Solid
4. High Specific Heat I’m pretty super!
5. Heat Of Vaporization
6. Ionization of Water
AP Biology
7. 1.Cohesion
Caused by the hydrogen bonds between
H2O molecules
Makes water “sticky”
Allows for this kid to drink out of his
straw Try that
with flour…
And this guy to walk on water or sugar…
AP Biology
8. 1. Adhesion
Caused by hydrogen bonding between
H20 and OTHER molecules
Causes meniscus
AP Biology
11. 2. Universal Solvent
Solvents dissolve solutes creating solutions
The polarity of H20 makes it a good solvent
polar H2O molecules surround + & – ions
pulling them apart
AP Biology
12. Noodle Time
Is any kind of liquid a good solvent?
Let’s try it!
AP Biology
13. What dissolves in water?
Hydrophilic
substances have attraction to H 2O
polar or non-polar?
AP Biology
14. What doesn’t dissolve in water?
Hydrophobic
substances that don’t have
an attraction to H2O
polar or non-polar?
AP Biology fat (triglycerol)
15. 3. Low Density as a solid (Ice Ice Baby)
Most substances are more dense when
they are solid, but
not water…
Ice floats!
H bonds form a crystal
And this has
made all the
difference!
AP Biology
17. Why is “ice floats” important?
Oceans & lakes don’t freeze solid
surface ice insulates water below
allowing life to survive the winter
if ice sank…
ponds, lakes & even oceans would freeze solid
in summer, only upper few inches would thaw
seasonal turnover of lakes
sinking cold H2O cycles nutrients in autumn
AP Biology
18. The Fireproof Balloon
NOODLE TIME!
What will explode first?
Pink - A balloon with H2O
Green - A balloon without H2O
Why did this happen?
AP Biology
19. 4. High Specific Heat
H2O resists changes in temperature
high specific heat
takes a lot to heat it up
takes a lot to cool it down
H2O moderates temperatures on Earth
AP Biology
20. Evaporative cooling
5. Heat of vaporization
Organisms rely on heat of
vaporization to remove body heat
AP Biology
22. 6. Ionization of water & pH
Water ionizes H2O → H+ + OH–
H+ splits off from H2O, leaving OH–
if [H+] = [-OH], solution is neutral
if [H+] > [-OH], solution is acidic
if [H+] < [-OH], solution is basic
pH scale
how acidic or basic a solution is
1 → 7 → 14
AP Biology
23. H+ Ion Examples of Solutions
Concentration pH
pH Scale 100
10–1
0
1
Hydrochloric acid
Stomach acid, Lemon juice
tenfold change 10–2 2
in H+ ions 10–3 3 Vinegar, cola, beer
10–4 4 Tomatoes
pH1 → pH2 10–5 5 Black coffee, Rainwater
10-1 → 10-2 10–6 6 Urine, Saliva
10 times less H +
Pure water, Blood
10–7 7
pH8 → pH7 10–8 8 Seawater
10-8 → 10-7 10–9 9 Baking soda
10 times more H+ 10–10 Great Salt Lake
10
pH10 → pH8 10–11 11 Household ammonia
10-10 → 10-8 10–12 12 Household bleach
100 times more H+ 10–13 13 Oven cleaner
10–14 14 Sodium hydroxide
AP Biology