1. Water and the Fitness of the Environment

2. A. Water and Hydrogen Bonding
Polar Molecule- asymmetric shape with opposite charges on opposite end
Hydrogen bonds- weak attractions of molecules to each other due to opposite charge

3. B. The Properties of Water

4. 1. Cohesion- water molecules cling to each other
1. Cohesion- water molecules cling to each other. This aids in the transport of water in plants

5. 2. Adhesion- water molecules cling to other substances
2. Adhesion- water molecules cling to other substances. Aids in the transport of water in plants
Adhesion

6. 3. High Surface Tension- at the interface between water and air, there is an ordered arrangement of water molecules

7. 4. High Specific Heat- water gains and loses heat slowly
4. High Specific Heat- water gains and loses heat slowly. This stabilizes temperatures within organisms and in their environment

8. 5. Water Expands when it Freezes- water contracts until about 4oC
5. Water Expands when it Freezes- water contracts until about 4oC. Then it expands because water molecules in ice are relatively far apart. This allows water to stay in liquid form in the winter

9. 6. Water is an excellent solvent- all polar compounds dissolve in water. This allows the transport of many important substances in organisms

10. 7. Water is clear- this allows light to penetrate to aquatic plants

11. Aqueous Solutions 1. Solution- a solute dissolved in a solvent
Solute- material that is dissolved
Solvent- material that dissolves the solute

12. 2. Concentration- the amount of solute in the solvent
Mole x 1023 molecules. Equal to the molecular weight of the substance in grams
Molecular weight- weight of all the atoms in a molecule.
Molarity- number of moles of a solute per liter of solution

13. Figuring Molecular Weight
Example: CO2
Carbon weighs Daltons
Oxygen #1 weighs Daltons
Oxygen #2 weights Daltons
CO2 weighs Daltons

14. D. Acids, Bases and pH Dissociation of water molecules: H2O H+ + OH-
At 25 oC the concentration of H+ and OH- is equal at 10-7 in pure water
Acids increase H+ in solution and decrease OH-
Bases decrease H+ in solution and increase OH-

15. pH Scale- Negative logarithm (Base 10) of the H+ ion concentration
In any solution, the sum of the OH- ions and H+ ions is 10-14
ions are inversely proportional
The pH scale is based on the power of 10
pH scale: fig 3.3 on p.54
Buffer- weak acids or bases that combine reversibly with H+ ions and therefore resist changes in pH