1. Figure 3.2 Hydrogen bonds between water molecules Evolution Living cells are 70-95% H2O H2O covers 3/4 of the planet Solid Liquid Gas Polarity and H-bonds Polar Bonds Asymmetrical shape and charge Resist change in temp Increase heat of vaporization Evaporative cooling Expands below 4 degrees C Solvent Cohesion Adhesion Surface tension Structural organization Maximum of 4 H bonds per H2O molecule

2. Heat and Temperature Kinetic energy = the energy of motion Heat = 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. Calorie (cal)= amount of heat it takes to raise the temperature of one gram of water one degree Celsius, also the amount of heat that one gram of water releases when it cools by one degree Celsius. Kilocalorie (Kcal or Cal) =1000 cal Water has a high specific heat, that is it resists temperature changes when it absorbs or releases heat. Specific heat = amount of heat that must be absorbed or lost for one gram of a substance to change its temperature by one degree Celsius. Specific heat of water = 1 cal per gram per degree Celsius (1 cal/g/ o C Evaporative cooling Vaporization (evaporation) = transformation from liquid to gas. Heat of vaporization = quantity of heat a liquid must absorb for 1 gram to be converted to the gaseous state. Water has a high heat of vaporization at the boiling point due to hydrogen bonding. (540 cal/g or 2260 J/g; Joule = 0.239 cal) Evaporative cooling = cooling of a liquid’s surface when a liquid evaporates. Moderation of the Earth’s climate Humidity

3. Figure 3.5 The structure of ice Water density Water is most dense at 4 o C Water contracts as it cools to 4 o C As water cools from 4 o C to freezing 0 o C, it expands and become less dense due to hydrogen bonding--therefore ice floats Benefit to life

4. Figure 3.6 A crystal of table salt dissolving in water Solution Homogenous mixture Solvent Dissolving agent Solute Substance dissolved Aqueous solution Water as a solvent Ionic and polar compounds dissolve in water Ionic and polar substances are hydrophilic, but nonpolar compounds are hydrophobic. Hydrophilic = water loving (some large hydrophilic molecules can absorb water without dissolving). Hydrophobic = water fearing, not water soluble.

5. Figure 3.9 A water-soluble protein Hydration Shell

6. There are 2 important quantitative properties of aqueous solutions: solute concentration and pH. Molecular weight = sum of the weight of all atoms in a molecule (expressed in daltons) Mole = amount of a substance that has mass in grams numerically equivalent to its molecular weight in daltons. All substances have the same number of molecules in a mole = 6.02 X 10 23 (Avogadro’s number). Molarity = number of moles of a solute per liter of solution.

7. Acid and Bases At equilibrium in pure water at 25 o C The number of H+ = the number of OH- [H+] =[OH-] = 1/10,000,000 or M= 10 -7 M Therefore very few molecules are dissociated (only 1 of 554,000,000). Acid = substance that increases the relative concentration of H+ of a solution. Base = substance that reduces the relative concentration of H+ of a solution. A solution in which: [H+] = [OH-] is neutral [H+] > [OH-] is acidic [H+] < [OH-] is basic Strong acids and bases dissociate completely in water e.g. HCl and NaOH. i.e. HCl H + + Cl - Weak acids and bases dissociate only partially and reversibly e.g. NH3 (ammonia) and H2CO3 (carbonic acid) pH Scale In any aqueous solution [H+]X[OH-] = 1.0 X 10 -14 In a neutral solution both = 10 -7 M In a basic solution where [H+] = 10 -9 M, the [OH-] = 10 -5 In a acidic solution where [H+] = 10 -5 M, the [OH-] = 10 -9 pH scale = scale used to measure degree of acidity (ranges from 0 to 14) pH = negative log10 of the [H+] expressed in moles per liter. pH of 7 is neutral pH < 7 is an acid solution pH > 7 is a basic solution

8. Figure 3.9 The pH of some aqueous solutions Most biological fluids are within the pH range of 6 to 8 (some exceptions e.g. stomach acid with a pH of 2.0) Each pH unit represents a tenfold difference (scale is logarithmic), so a small change in pH represents a large change in actual [H+].

9. Buffers Buffer = substance that minimizes large sudden changes in pH---helps organisms maintain the pH of body fluids within a narrow range. Buffers are combinations of H+ donor and H+ acceptor forms in a solution of weak acids or bases. They work by accepting H+ ions from a solution when they are in excess and by donating H+ ions to the solution when they have been depleted. e.g. Bicarbonate buffer H2CO3 HCO3- + H+ H+ donorH+ acceptor (weak acid)(weak base)