Water (H2O)
Most important inorganic molecule in living things.
Living organisms = 75-80% H2O. Many biological processes require H2O
› Survive 21-24 days without food› Survive 3 days without water
Properties of Water
Buoyancy Polarity Cohesion Adhesion Surface Tension High Specific Heat Forms solutions Neutral pH
Heats Slowly & Cools Slowly
High Specific Heat- a lot of heat is needed to raise the temperature of 1 gram of H2O by 1°C
H2O retains heat & cools slowly.› Ex: pool/ocean is warm in the fall.
Allows organisms to maintain relatively constant body temperatures.
Polar Molecule
Atoms of different elements don’t always share e- equally.
› More protons (+) in the nucleus means a stronger attraction for electrons (-).
Polar Molecule
e- drawn the nucleus with more protons MORE than the others. › Charges form polar molecules or polar
regions of large molecules
Cohesion- ability of H2O molecules to resist coming apart. › Keeps H2O molecules together as they
move from roots to leaves.
Giant Sequoia
Cohesion and Surface Tension How droplets of H2O form. Attraction between H2O molecules
surface tension› Surface Tension- molecules in the
surface layer are H-bonded to H2O molecules below them.
› Prevents water’s surface from easily breaking.
Water Strider Droplet Formation
Adhesion- attraction between H2O molecules and molecules of other substances (that can form H-Bonds). › Due to polarity of H2O
› Other polar substances get wet (mix with H2O)
› Nonpolar molecules, like oils, do not.
Adhesion
Adhesion and Capillary Action
Attraction of H2O to surfaces with a charge capillary action
Capillary Action- tendency of liquids to rise in tubes of small diameter.› Explains movement of H2O from roots
leaves
Forms Solutions Many substances dissolve in H2O. Solution- mixture in which 1+ substances
are evenly distributed in another substance.› Can be mixtures of liquids, solids, or gases.› Substances transported in organisms as
solutions of water. Ex: Plasma (liquid part of blood)- made up of
various ions and macromolecules, as well as gases, that are dissolved in H2O.
Parts of Solutions Solute- substance being dissolved.
› Ex: Sugar Solvent- substance in which solute is
dissolved. › Ex: H2O
Sugar + H2O Sugar H2O
**Sugar & H2O molecules remain unchanged and can be separated again.**
Low Density Solid Ice (solid) is LESS dense than liquid
H2O.
Acids and Bases Bonds break between some water
molecules as they collide.› Forms a H ion (H+) and a hydroxide ion
(OH-).
Pure H2O ALWAYS has a low concentration of H+ and OH- ions
H+ ions = OH- ions
Acids and Bases Compounds that form H+ when
dissolved in H2O are acids.› Adding acids to pure H2O H+ level
increases above that of pure H2O
Bases- compounds that reduce [H+] in a solution.› Many bases form OH- when dissolved in
H2O.
› Lower [H+] because OH- reacts with H+ to form H2O.
Acids and Bases pH scale- measures H+ concentration
in a solution.
Acids and Bases Each whole # (on pH scale) represents
a factor of 10. › Solution with pH 5 has 10 times more H+
than a solution with pH 6. › Note: Stomach acid pH= 2 Blood pH=
7.5
Questions1. Lemons have a pH of 2. Are lemons
acidic or basic?2. The strongest bases have a pH of ____.3. Pure water is a neutral substance.
What is the pH of pure water?
Animations/Tutorials/Videos Matter:
http://www.teachersdomain.org/asset/lsps07_int_naturematter/ Matter Video Review:
http://www.teachersdomain.org/asset/psu06-nano_vid_matter/ Atomic Structure:
http://www.teachersdomain.org/asset/lsps07_int_theatom/ Chemical Bonding:
http://www.teachersdomain.org/asset/lsps07_int_chembonds/ Water Video:
http://www.teachersdomain.org/asset/idptv11_vid_d4ksow/ NOVA Hunting the Elements Video:
http://www.pbs.org/wgbh/nova/physics/hunting-elements.html