Ch. 3 Reading Quiz What are the bonds BETWEEN water molecules called? What CAUSES hydrogen bonding? What does it mean to be hydrophilic? Anything with a pH of 0 – 6 is known as a what? Anything with a pH of 8 - 14 is known as a what? Hydrogen bonds polarity Attracted to water acid base

1. Describe how water contributes to life. Life on earth probably evolved in water Living cells are 70 – 95% water Water covers ¾ of earth Water exists naturally in it’s 3 states on earth – solid, liquid, gas 

Prizes from yesterday…

Polar bonds and asymmetrical shape give opposite charges 2. Describe the structure and geometry of a water molecule, and explain what properties emerge as a result of this structure. Polar bonds and asymmetrical shape give opposite charges 2 “corners” are occupied by hydrogens 2 “corners” have unshared pairs of electrons Oxygen is so electronegative that the atoms have partial charges 

3. Explain the relationship between the polar nature of water and its ability to form hydrogen bonds. Polar molecules are held together by H bonds The + charged hydrogen atom is attracted to the – charged oxygen Each water molecule can form a maximum of 4 hydrogen bonds with other water molecules 

Resists temperature change 4. List the characteristics of water that are emergent properties resulting from hydrogen bonding. Cohesive behavior Resists temperature change High heat of vaporization & cools as it evaporates Expands when it freezes Is a versatile solvent 

5. Describe the biological significance of the cohesiveness of water. Cohesive/cohesion = the phenomenon of a substance being held together by hydrogen bonds Enough hydrogen bonds are in water at any given time to give water more structure than other liquids Contributes to transport in PLANTS; adhesion of water the vessel walls counteracts gravity – forms ‘capillary action’ 

6. Distinguish between heat and temperature. Total kinetic energy due to molecular motion in a body of matter Temperature Measure of heat intensity due to the average kinetic energy of molecules in a body of matter 

Expansion upon freezing 7. Explain how water’s high specific heat, high heat of vaporization and expansion upon freezing affect both aquatic and terrestrial ecosystems. Specific Heat 1 cal/ g/ ‘C Allows a large body of water to act as a ‘heat sink’; provides a stable temperature & environment Ex: desert vs. coast climates Heat of Vaporization the amount of heat a liquid must absorb to have 1 g become gaseous moderates climate, stabilizes temperature, allows for evaporative cooling Expansion upon freezing water is densest at 4’C Expansion due to H bonds getting further apart Allows for ice to float – lakes don’t freeze solid (acts as insulation)

8. Explain how the polarity of the water molecule makes a versatile solvent. (hydrophilic vs. hydrophobic) Hydrophilic Charged regions of polar water molecules have an electrical attraction to charged ions (an affinity for other polar molecules) Hydrophobic Nonpolar compounds (have a symmetrical distribution of charge) Are NOT water soluble 

Molarity – number of moles of solute per liter of solution 9. Define molarity and list some advantages of measuring substances in moles. Molarity – number of moles of solute per liter of solution Advantages – 1. upscales weighing of single molecules from daltons to grams 2. A mole (mol) of one substance has the same number of molecules as a mole of any other substance (6.02 x 1023) 3. Allows one to combine substances in fixed ratios of molecules 

10. Write the equation for the dissolution of water, and explain what is actually transferred from one molecule to another. H2O + H2O  H3O+ + OH- (waters) (hydronium ion) (hydroxide ion) Only a H+ ion is actually transferred; it binds to the unshared orbital of the 2nd H2O molecule making H3O+ Is expressed as the dissociation into H+ and OH- The reaction is reversible At equilibrium, most H2O is not ionized Only 1 out of 554,000,000 H2O molecules are dissociated 

11. Explain the basis for the pH scale, and describe how acids and bases affect the hydrogen ion concentration of a solution. pH scale is used to measure the degree of acidity 0-14 Strong acids and bases dissociate completely in water (Ex: NaOH  Na+ + OH- ; HCl  H+ + Cl- ) Acids increase the relative [H+] in a solution Bases reduce the relative [H+] in a solution [H+] = [OH-] in a neutral solution [H+] > [OH-] in an acidic solution [H+] < [OH-] in a basic solution 

(H+ donor, w.a.) (H+ acceptor, w.b.) (ion) 12. Using the bicarbonate buffer system as an example, explain how buffers work. H2CO3  HCO3 + H+ (H+ donor, w.a.) (H+ acceptor, w.b.) (ion) Buffer = a substance that minimizes large sudden changes in pH - works by accepting H+ ions from solution where there is excess and donates H+ ions to the solution where they are depleted (s.a.) (buffer) (w.a.) Acid ex: HCl + NaHCO3  H2CO3 + NaCl Base ex: NaOH + H2CO3  NaHCO3 + H2O (s.b.) (buffer) (w.b.) 

13.  Describe the causes of acid precipitation, and explain how it adversely affects the fitness of the environment. Acid precipitation = rain/snow/fog more strongly acidic that pH 5.6 (lowest recorded 1.5 in VA) Causes = 1. Sulfur & nitrogen oxides in atmosphere react w/H2O to form acids 2. Major source is fossil fuel combustion Effects = 1. Lowers soil pH & affects mineral solubility (may leach out nutrients and increase toxicity) 2. Lowers pH of lakes, runoff carries bad soil into aquatic ecosystems Ex: Adirondack Mtns with lakes pH <5 = no fish! 