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Figure 3-01

Figure 3-01. 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”

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Figure 3-01

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  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

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

  4. Figure 3-04

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

  6. 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)

  7. 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.

  8. 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.

  9. 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

  10. LE 3-UN53 Hydronium ion (H3O+) Hydroxide ion (OH–)

  11. 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.

  12. 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

  13. Ph Scale

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

  15. 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

  16. 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?

  17. Buffering Systems

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