Chapter 3: Water and the Fitness of the Environment

I. Importance of Polarity Polarity in water results in hydrogen bonding One water molecule can create 4 hydrogen bonds

II. Unique Characteristics of Water Cohesion Moderates Temperature Density Use as a solvent

A. Cohesion Water molecules stick together, why? -cohesion, hydrogen bonds hold water together Adhesion - substances sticking together High Surface Tension

B. Moderating Temperature Water absorbs and releases heat with little temperature change - heat: measure of the total quantity of kinetic energy - temperature: measure the intensity of heat due to average kinetic energy - specific heat: measure of how well a substance resists changing its temperature when it absorbs or releases heat

B. Moderating Temperature (cont.) Water has a very high specific heat, 10X iron Water resists temperature change because hydrogen bonds have to be broken to raise the temperature which takes a lot of heat / energy Maintains temperature of oceans, organisms, and Earth Water has a high heat of vaporization which allows for evaporative cooling

C. Density Water is less dense in solid form then liquid form Water freezes when it can no longer break H-bonds. H-bonds become rigid when they can not break and form a matrix Ecological implications?

D. Solvent Solvent, Solute, and Solution Great solvent for ionic solutions and polar molecules Aqueous Solution - one with water as the solvent Hydrophobic vs. Hydrophilic

III. Mole Mole (mol) - equal in number to the molecular weight of a substance but upscaled from daltons to units of grams. One mole of table salt would weigh… 58 grams Avagadro’s number - number of molecules in a mol 6.02 x 1023 Molarity - number of moles of solute per liter of solution

IV. pH Hydrogen Ion - single proton with a charge of +1 (H+) Hydroxide Ion - (OH-) charge of -1 Dissociation - transfer of H+ ions

H20 goes back and forth H+ and OH-

A. Acid Substance that increases the H+ concentration of a solution Acids donate H+ ions to a solution Examples: HCL and H2SO4

B. Base Substance that increases the OH- concentration of a solution. It can do this by giving off OH- ions or taking on H+ ions Examples: NaOH and NH3 (why?)

V. pH Scale Scale ranging from 0-14 and expresses the concentration of H+ ions in a solution. Product of OH- and H+ concentrations is always 10-14. Defined as -log(H+) base 10 pH declines as H+ concentrations increase Each pH unit represents a 10 fold difference in H+ and OH- concentrations

VI. Buffer Substance that minimizes the change of pH in a substance Accepts and donates ions in solution when needed Usually an acid-base pair like H2CO3 in blood