Water and the Fitness of the Environment - Notes PDF

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Detailed notes on Chapter 3 , Water and Fitness of the Environment. These notes are helpful for any assignments regarding this topic....

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Water and the Fitness of the Environment

The Polarity of Water Molecules Results in Hydrogen Bonding ● The structure of water is the key to its special properties ● 1 atom of oxygen and 2 atoms of hydrogen ● Water molecules are polar ✓ Oxygen end has a slight negative charge ✓ Hydrogen end has a slight positive charge ● Hydrogen bonds form between water molecules when the slight negative oxygen atom of one water molecule is attracted to the slight positive hydrogen atoms of another water molecule ✓ Each water molecule can form a maximum of 4 H-bonds ✓ Very weak Four Emergent Properties of Water Contribute to Earth’s Fitness for Life ● The key to each of these properties is hydrogen bonds 1. Cohesion is when water molecules are joined together ✓ Adhesion is the clinging of one substance to another ➢ Water molecules attached to another type of molecule ✓ Transpiration is the movement of water molecules up the very thin xylem tubes and their evaporation from the stomates in plants. The water molecules cling to each other by cohesion and the xylem walls by adhesion. 2. Moderation of temperature ✓ Made possible by water’s high specific heat ➢ The amount of heat required to raise or lower the temperature of a substance by 1 degree Celsius ➢ Makes the temperature of Earth’s oceans relatively stable and able to support a great deal of plant and animal life 3. Insulation of bodies of water by floating ice ✓ Water’s solid state is less dense than its liquid state ✓ Solid water forms a crystal lattice structure in which each water molecule is bonded to 4 other water molecules ✓ Ice floats because it is less dense than liquid water ✓ This prevents large bodies of water from freezing solid 4. Water is an important solvent ✓ A solvent is the substance that something is dissolved in

✓ A solute is the substance that dissolves in the solvent ✓ Aqueous solutions are solutions in which water is the solvent ✓ Hydrophilic substances are water-soluble ➢ Ionic and polar compounds ✓ Hydrophobic substances do not dissolve in water ➢ Nonpolar compounds Acidic and Basic Conditions Affect Living Organisms ● Caused by dissociation of water molecules ✓ A hydrogen ion is transferred from one water molecule to another, has a charge of +1 ✓ End up with a hydroxide ion (OH-) and a hydronium ion (H3O+)

● The pH scale runs between 0 and 14 and measures the relative acidity and alkalinity of aqueous solutions ✓ Acids have an excess of H+ ions and a pH below 7.0; [H+] > [OH-] ✓ Bases have an excess of OH- ions and a pH above 7.0; [H+] < [OH-] ✓ Pure water is neutral and has a pH of 7.0; [H+] = [OH-] ● Buffers are substances that minimize changes in pH; they accept H+ from a solution when they are in excess and donate H+ when they are depleted ● Carbonic acid (H2CO3) is an important buffer in living systems; it moderates pH changes in blood and in the oceans...