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Chapter 3

Chapter 3. Water and the Fitness of the Environment. Figure 3.1. The Water Planet. Three-quarters of the Earth’s surface is submerged in water The abundance of water is the main reason the Earth is habitable. Polarity of Water Molecules.

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Chapter 3

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  1. Chapter 3 Water and the Fitness of the Environment

  2. Figure 3.1 The Water Planet • Three-quarters of the Earth’s surface is submerged in water • The abundance of water is the main reason the Earth is habitable

  3. Polarity of Water Molecules • The polarity of water molecules allows them to form hydrogen bonds with each other • Each water molecule can form 4 hydrogen bonds with neighboring water molecules • Hydrogen bonding contributes to the properties of water – Hydrogenbonds + H – + H + –  – + Figure 3.2

  4. Cohesion • Cohesion • Is the bonding of a high percentage of the molecules to neighboring molecules • Is due to hydrogen bonding • Helps pull water up through the microscopic vessels of plants Water conducting cells 100 µm Figure 3.3

  5. Figure 3.4 Surface Tension • Surface tension • Is a measure of how hard it is to break the surface of a liquid • Is related to cohesion

  6. Water’s High Specific Heat • The specific heat of a substance • Is the amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1ºC • Water has a high specific heat, which allows it to minimize temperature fluctuations to within limits that permit life

  7. Moderation of Temperature • Water moderates air temperature • By absorbing heat from air that is warmer and releasing the stored heat to air that is cooler • Heat is absorbed when hydrogen bonds break • Heat is released when hydrogen bonds form

  8. Heat and Temperature • Kinetic energy • Is the energy of motion • Heat • Is a measure of the total amount of kinetic energy due to molecular motion • Temperature • Measures the intensity of heat

  9. Evaporative Cooling • Evaporation • Is the transformation of a substance from a liquid to a gas • Heat of vaporization • Is the quantity of heat a liquid must absorb for 1 gram of it to be converted from a liquid to a gas

  10. Evaporative Cooling • Evaporative cooling • Is due to water’s high heat of vaporization • Allows water to cool a surface

  11. Ice is less dense than water • The hydrogen bonds in ice • Are more “ordered” than in liquid water, making ice less dense Figure 3.5 Ice Hydrogen bonds are stable Liquid water Hydrogen bonds constantly break and re-form

  12. Insulation of Bodies of Water by Floating Ice • Solid water, or ice • Floats in liquid water because it is less dense • Since ice floats in water • Life can exist under the frozen surfaces of lakes and polar seas

  13. The Solvent of Life • Water is a versatile solvent due to its polarity • It can form aqueous solutions • The different regions of the polar water molecule can interact with ionic compounds called solutes and dissolve them

  14. – Na+ + + – + – Positive hydrogen regions of water molecules cling to chloride anions (Cl–). – Na+ – + + Cl – Cl– + – – + – + – – Figure 3.6 A crystal of table salt dissolving in water Negative Oxygen regions of polar water molecules are attracted to sodium cations (Na+).

  15. The Solvent of Life • Water can also interact with polar molecules such as proteins • Ionic and polar regions on the protein’s surface attract water molecules. This oxygen is attracted to a slight positive charge on the lysozyme molecule. – + (b) Lysozyme molecule (purple) in an aqueous environment such as tears or saliva (a) Lysozyme molecule in a nonaqueous environment This hydrogen is attracted to a slight negative charge on the lysozyme molecule. Figure 3.7

  16. Hydrophilic and Hydrophobic Substances • A hydrophilic substance • “water loving” • Has an affinity for water • A hydrophobic substance • “water fearing” • Does not have an affinity for water

  17. Solute Concentration in Aqueous Solutions [Solute] + [Solvent] = [Solution] = 100% The solute is the dissolved substance (eg salt) The solvent is the dissolving agent (eg water) A solution is a homogeneous mixture

  18. + – H H H + H H H H H Hydroxide ion (OH–) Hydronium ion (H3O+) Figure on p. 53 of water dissociating Dissociation of Water • Water can dissociate • Into hydronium ions and hydroxide ions • Changes in the concentration of these ions • Can have a great affect on living organisms

  19. Acids and Bases • An acid • Is any substance that increases the hydronium ion concentration of a solution • A base • Is any substance that reduces the hydronium ion concentration of a solution

  20. The pH Scale • The pH of a solution • Is determined by the relative concentration of hydrogen ions • pH values from 0-7 are acidic • pH values from 7-14 are basic • A pH equal to 7 is neutral

  21. pH Scale 0 1 Battery acid 2 Digestive (stomach) juice, lemon juice 3 Vinegar, beer, wine, cola Increasingly Acidic [H+] > [OH–] 4 Tomato juice 5 Black coffee Rainwater 6 Urine Neutral [H+] = [OH–] 7 Pure water Human blood 8 Seawater 9 10 Increasingly Basic [H+] < [OH–] Milk of magnesia 11 Household ammonia 12 Household bleach 13 Oven cleaner 14 Figure 3.8 The pH scale and pH values of some aqueous solutions

  22. Buffers • The internal pH of most living cells • Must remain close to pH 7 • Buffers • Are substances that minimize changes in the concentrations of hydrogen and hydroxide ions in a solution • Consist of an acid-base pair that reversibly combines with hydrogen ions

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