1. Water

2. The unequal distribution of electrons makes
water a polar molecule (+/- regions)
Oxygen is more
electronegative than
hydrogen
This propensity to bond mean water sticks to itself, to other charged atoms and molecules, and greater the electrical attraction, the more energy is required to break those bonds.
640::480::/sites/dl/free/ /811313/Polarity.mov::Polarity

3. interacts with water does not interact

4. Since opposite charges attract, polar molecules form hydrogen
Bonds, ‘sticking’ together
This is cohesion
H- bonds are one type of Van de Waals force -
the attraction of two of the same type of molecule

5. strongest at the surface – called surface tension
Cohesion between
adjacent molecules is
strongest at the surface
– called surface tension

6. Molecules that do not form
H bonds are non-polar
Non-polar substances are
hydrophobic

7. Water forms H bonds with other polar molecules and ions
This is adhesion
Adhesion creates a meniscus
capillary action
results from both adhesion and cohesion

8. Water is a solvent for solutes that are charged i. e
Water is a solvent for solutes that are charged i.e. salt (ionic) & sugar (polar covalent)
Na+ and Cl- dissociate
in water, creating a
solution
NaCl is hydrophillic

9. Water transpired to atmosphere
Cohesion, adhesion and capillary action transport water throughout a plant

10. Water will spontaneously decompose,
albeit in small amounts: 1 x in pure H2O
This is used to set the neutral value of pH at 7
2H2O
H3O+
hydronium
OH-
hydroxide
Simplified as: H+
Creates charged ions

11. Some solutes affect the concentration of H+ ions
in a solution, altering the sol’ns pH (% hydrogen)
Acids
• act as H+ donors,
• lowers the pH
Pure water is neutral; pH = 7
1/1000,000 molecule decomposes
Bases
• act as H+ acceptors
• OH left behind in sol’n
• increases the pH

12. H2O HCl --- H+ + Cl- acid neutral base H+ H+ H+ H+ H+ H+ H+ H+ H+ H+
NaOH --- Na+ + OH-

13. • Buffers moderate changes in pH by interacting
with (acting as a reservoir for) H+ or OH-

14. Strong vs Weak it’s not about pH
Refers to the percent of the molecules that will dissociate in water
strong = all molecules dissociate weak = only some (few) will
Acetic acid (vinegar)
and
bicarbonate (baking soda)
HCl
and
NaOH

15. Any strong acid or base is dangerous!
Wear goggles and gloves
NaOH burn

16. So what?
pH changes disrupts charge, affects enzyme function

17. Water has a high specific heat –
it takes a lot of energy to raise it’s temp
Brooks
Inst of Photo.
Pitzer
College
70 F
80F
90F
100F
Univ. of
Redlands
Relatively
constant
ocean temp
USD
Therefore it does not gain or lose heat rapidly
Large bodies of water act to regulate climate

18. High internal water content of organisms lets
them maintain a stable internal temp

19. Water has a high heat of vaporization
Changing state from liquid to gas takes energy,
therefore sweat is cooling

20. Solid water is less
dense than liquid
so..
…ice floats; ponds and lakes remain habitable in winter

21. Water in zero gravity