Water's Fitness for Life: Understanding Its Unique Properties

1. CHAPTER 3 WATER AND THE FITNESSOF THE ENVIRONMENT

2. I. Water’s Polarity and Its Effects • A. The polarity of water molecules results in hydrogen bonding • A HYDROGEN BOND FORMS WHEN THE OXYGEN OF ONE WATER MOLECULE IS ELECTRICALLY ATTRACTED TO THE HYDROGEN OF A NEARBY MOLECULE. • HYDROGEN BONDING BETWEEN WATER MOLECULES IS THE BASIS OF WATER’S UNUSUAL PROPERTIES.

4. Figure 3.0 Earth

5. SPECIAL PROPERTIES OF WATER • COHESION • ADHESION • HIGH SURFACE TENSION • HIGH HEAT CAPACITY • DENSITY • VERSATILE SOLVENT

7. Figure 3.1 Hydrogen bonds between water molecules 

8. Figure 3.1 Hydrogen bonds between water molecules 

9. B. Organisms depend on the cohesion of water molecules • HYDROGEN BONDING MAKES WATER MOLECULES STICK TOGETHER, AND THIS COHESION HELPS PULL WATER UPWARD IN THE MICROSCOPIC VESSELS OF PLANTS. Figure 0301 HYDROGEN BONDS B/W MOLECULES • HYDROGEN BONDING IS ALSO RESPONSIBLE FOR WATER’S SURFACE TENSION. • SURFACE TENSION: A measure of how difficult it is to stretch or break the surface of a liquid.

13. C. Water moderates temperatures on Earth • HYDROGEN BONDING GIVES WATER A HIGH SPECIFIC HEAT. • SPECIFIC HEAT = The amount of heat that must be absorbed or lost for 1 g of a substance to change its temperature 1° C. • HEAT IS ABSORBED WHEN H+ BONDS BREAK AND IS RELEASED WHEN H+ BONDS FORM, MINIMIZING TEMP. FLUCTUATIONS TO WITHIN LIMITS THAT PERMIT LIFE.

14. Figure 3.4 Evaporative cooling

15. D. Oceans and lakes don’t freeze solid because ice floats • ICE IS LESS DENSE THAN LIQUID WATER B/C ITS MORE ORGANIZED H+ BONDING CAUSES EXPANSION INTO A CRYSTAL FORMATION. • FLOATING ICE ALLOWS LIFE TO EXIST UNDER THE FROZEN SURFACES OF LAKES AND POLAR SEAS. Figure 0305 THE STRUCTURE OF ICE

19. Figure 3.5 The structure of ice (Layer 1)

21. Figure 3.5 The structure of ice (Layer 2)

23. Figure 3.5x1 Ice, water, and steam

25. Figure 3.6 Floating ice and the fitness of the environment

27. Figure 3.6x1 Floating ice and the fitness of the environment: ice fishing

29. Figure 3.6x2 Ice floats and frozen benzene sinks

30. E. Water is the solvent of life • WATER IS AN UNUSUALLY VERSATILE SOLVENT B/C ITS POLARITY ATTRACTS IT TO CHARGED POLAR SUBSTANCES. • WHEN IONS OR POLAR SUBSTANCES ARE SURROUNDED BY WATER MOLECULES, THEY DISSOLVE AND ARE CALLED SOLUTES. • HYDROPHYLIC = “LIKE” WATER • HYDROPHOBIC = “FEAR” WATER Figure 0307 A CRYSTAL OF TABLE SALT DISSOLVING IN WATER Figure 0308 A WATER SOLUBLE PROTEIN

32. II. The Dissociation of Water A. Organisms are sensitive to changes in pH • WATER CAN DISSOCIATE INTO H+ AND OH- • THE CONCENTRATION OF H+ IS EXPRESSED AS pH. • ACIDS DONATE ADDITIONAL H+ IN AQUEOUS SOLN’S. • BASES DONATE ADDITIONAL OH- IN AQUESOUS SOLN’S. • pH SCALE: A measure of hydrogen ion concentration ranging in value from 0 to 14. • ACID = 0-7 • NEUTRAL = 7 • BASE = 7 – 14 Figure 0309 THE pH OF SOME AQUEOUS SOLUTIONS

34. Unnumbered Figure (page 47) Chemical reaction: hydrogen bond shift