Water ~ H 2 O

1. Water ~ H2O Some unusual properties

2. 1. Water cohesive and adhesive. • Cohesion - holding together of LIKE substances. • Adhesion - holding of different substances to each other. • eg: surface tension - eg: water acts “sticky”, like it has a “skin” • Surface tension -is due to cohesion of water mycs to one another by hydrogen bonds. • adhesive & cohesive nature of water explains capillary action: • movement of water up a piece of porous paper, through the pores in leaves or soil, or into a germinating seed.

3. 2. Water has high specific heat • Specific heat - amt of energy needed to raise the temp of 1 gram of a substance by 1 degree C. • Takes a lot of heat = to raise the temp of water...and • much heat must be lost to lower its temperature. • Result: body of water warms slowly in spring, cools slowly in the fall; gradual temp changes. • Living things (high % of water) gain & lose heat slowly. • organisms - temp doesn’t fluctuate wildly. • they gain and loose heat very slowly.

4. 3. High boiling Point of H2O • takes a lot of heat energy to overcome all the “hydrogen bonds” between water mycs...and to change water from liquid to gas... • temps on earth seldom reach the boiling point, so organisms won’t have to worry about boiling away. • eg: alcohol...low bp, • eg: acetone

5. 4. Water is a good evaporative coolant • Water mycs - change from liquid to gas by absorbing enough heat to escape the liquid into the air. • When they escape the body, they carry away a lot of heat energy. • eg. humans sweat; dogs pant... • Lick finger - place outside moving car.

6. 5. Water has high freezing point + lower density as a solid than as liquid. • As warm water cools, mycs lose energy, move closer together; H bonding holds them closer together. • Water becomes more dense. • * water is peculiar ! - Max density occurs at 40 C • As water cools, from 40 C to freezing, it expands again, becoming less dense (mycs move apart) forming ice which floats.

7. 5. continued • Some organisms have adaptations - allow them to survive freezing tems. • Winter wheat, some insects, fish, and frogs have antifreezes - often glycerol (used in car’s antifreeze)

8. 6. Water is a solvent • More substances dissolve in water than any other liquid. • Substance dissolves - mycs or ions separate, mingle with solvent (= water mycs) • Polar mycs of water - attracted to charged ions and to other polar mycs. • “Likes dissolve likes”