Water http://www.youtube.com/watch?v=HW5eBfZhE4M

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. http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=mov:: 640::480::/sites/dl/free/0073532223/811313/Polarity.mov::Polarity

interacts with water does not interact

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

strongest at the surface – called surface tension Cohesion between adjacent molecules is strongest at the surface – called surface tension http://dsc.discovery.com/videos/time-warp-water-droplet.html

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

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

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

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

Water will spontaneously decompose, albeit in small amounts: 1 x 10 -7 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

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

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

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

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

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

So what? pH changes disrupts charge, affects enzyme function

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

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

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

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

Water in zero gravity http://www.youtube.com/watch?v=ntQ7qGilqZE