1. Figure 3-01

2. Water is Central to Life Water has several properties that life is dependent upon including: Cohesion High heat of vaporization High specific heat Less dense as a solid than a liquid A “universal solvent” All of these properties are due to the polar nature of water molecules and hydrogen bonding

4. LE 3-3 Water-conducting cells 100 µm

5. Figure 3-04

6. LE 3-6 Na + Cl – + + + + + + + + – – – – – – – – – – –

7. Dissociation Many molecules will dissociate when the are placed in water Ions are separated and “released” into the water environment Table salts dissolves in water (dissociates into sodium and chlorine ions)

8. Acids When hydrogen chloride is placed in water it dissociates into Hydrogen ions (H+) and chlorine ions (Cl-) HCl is an acid Acids are substance that release H+ ions (protons) when they dissociate in water The more acidic a solution, the higher concentration of H+ ions (protons) it has.

9. Bases When sodium hydroxide is placed in water it dissociates into sodium ions (Na+) and hydroxide ions (OH-) NaOH is a base Bases are substance that release OH- ions when they dissociate in water The more acidic a solution, the higher concentration of OH- ions it has.

10. Water Dissociates Water molecules are not completely stable They spontaneously dissociate (at a very slow rate) into H+ and OH- ions. At any given moment only 1/554,000,000 water molecules in pure water dissociates

11. LE 3-UN53 Hydronium ion (H 3 O + ) Hydroxide ion (OH – )

12. Spontaneous Dissociation of Water Is water and acid? Is it a base? Water is amphoteric At equilibrium, the [H+] concentration is 1X10-7 M. At equilibrium, the [OH-] concentration is 1X10-7 M.

13. pH Scale pH is the –log [H+] The pH scale measure the acidity (or basicity) of an aqueous solution The pH scale range from 0-14 The lower the pH, the higher the [H+] The higher the pH the lower the [H+] A pH of 7 is considered to be neutral

14. Ph Scale

15. LE 3-8 pH Scale 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Oven cleaner Household bleach Household ammonia Milk of magnesia Seawater Pure water Human blood Urine Rainwater Black coffee Tomato juice Vinegar, beer, wine, cola Digestive (stomach) juice, lemon juice Battery acid Neutral [H + ] = [OH – ] Increasingly Acidic [H + ] > [OH – ] Increasingly Basic [H + ] < [OH – ]

16. The importance of pH to life Living things typically exist is an aqueous environment The pH of the environment influences the charge of molecules present in that environment The charge of molecules influences their shape (structure) The shape of molecules determines their function

17. Case study-pH and Blood The normal pH of blood is about 7.4 What are the consequences of a change in that pH? Effect on hemoglobin? Why is hemoglobin affected by a change in pH? What homeostatic mechanisms does the blood have to keep its pH constant?

18. Buffering Systems