Properties of WaterChapter 2

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

Three Physical States of H2O

Solid (ice)

Liquid

Gas (vapor)

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