Water ä Water is necessary for life ä Life evolved in water

Water ä Cells are 70-90% water

Water ä 75% of Earth covered by water

Water is Polar ä Uneven distribution of electrons ä Partial charge distribution

Hydrogen Bonds   + hydrogen attracted to  oxygen of neighboring molecule ä up to 4 bonds per molecule

Cohesion ä Water molecules hydrogen bonding to other water molecules surface tension

Adhesion ä Water molecules hydrogen bonding to other substances

Water Transport in Plants ä Cohesion, adhesion, & evaporation combine to lift water to tree tops

Phases of Water ä Only substance to exist in three phases at normal Earth temperatures solid liquid gas

Temperature ä Average molecular kinetic energy of an object ä Measured with thermometer

Temperature ä Standard unit is degree Celsius (°C) “Thirty is hot Twenty is nice Ten is chilly Zero is ice.” 0 °C water freezes 10 °C 20 °C 30 °C 100 °C water boils body 37 °C

Heat ä Energy moving from a hotter substance to a colder substance 30°C10°C heat

Heat ä Standard unit is calorie caloriecal kilocalorieCal jouleJ

Specific Heat ä Amount of heat it takes to raise the temperature of 1 g of a substance 1°C

Specific Heat of Water ä Water has a very high specific heat specific heat H 2 O = 1 cal/g/°C

Specific Heat ä Added heat used to break hydrogen bonds, not speed up molecules ä Forming hydrogen bonds releases considerable heat

Water Moderates Temperatures ä Oceans & large lakes change temperature very slowly ä Moderates coastal climates ä Water-filled cells resist changes in temperature

Phase Changes in Water Heat of Vaporization 540 cal/g Heat of Fusion 80 cal/g

Changing Phase ä Heat of vaporization - heat required to change 1 g of water to 1 g of vapor

Changing Phase ä Water has high heat of vaporization due to hydrogen bonds heat vaporization H 2 O = 540 cal/g

Evaporative Cooling ä Evaporation cools remaining water

Heat Distribution ä Evaporation cools tropical oceans ä Condensation of vapor at higher latitudes releases heat

Ice Floats ä Solid less dense than liquid ä Expands as it freezes Hydrogen bonds in ice keep molecules separated

Ice Floats ä Water densest at 4°C ä Expands as it cools from 4°C to 0°C and freezes 4°C 0°C

Ice Floats ä Floating ice insulates water below from freezing 4°C 0°C

Solutions ä Molecules or atoms of the solute are evenly distributed throughout the solvent Sugar solutesolvent

“Universal Solvent” ä Water is a very versatile solvent because it is polar 1 st Place

Ionic Solutions ä Solute dissolves by separating into ions ä NaCl

Polar Compounds ä Dissolve in water ä Sugars, proteins

Hydrophilic ä “water loving” ä Substance with affinity for water ä Ionic & polar solutes ä Cotton

Hydrophobic ä “water fearing” ä Substance without an affinity for water ä Non-ionic & nonpolar solutes ä Oils

Mole = amount equal to gram equivalent of molecular weight of solute Solute Concentration ä Measured as molarity

Mole ä Ex. table sugar C 12 H 22 O 11 ä Molecular weight = 12(12) + 22(1) + 11(16) = 342 da 1 mole sucrose weighs 342 g

Mole ä A mole of any substance contains 6.02 x molecules Avogadro’s number yum

Molarity ä Number of moles solute per liter of total solution ä Dissolving 1 mole solute in enough water to make 1 liter of solution creates a 1 molar (1M) solution

342 g Molarity 1L Sugar 1M aqueous sucrose solution

Dissociation of Water H 2 O H + + OH - hydrogen ion hydroxide ion

Dissociation of Water ä Only 1 molecule in every 554 million dissociates ä Concentrations of H + & OH - is M at 25°C

Acids ä Compounds that release H + ions into solution HCl H + + Cl - H 2 SO 4 H + + SO 4 -- HNO 3 H + + NO 3 -

Acid ä Carbonic acid is a weak acid ä 1% of molecules dissociate H 2 CO 3 HCO H +

Bases ä Compounds that release OH – ions into solution NaOH Na + + OH - Ca(OH) 2 Ca (OH - ) KOH K + + OH -

Base ä Ammonia reduces H + concentration NH 3 + H + NH 4 +

Acids & Bases ä A solution in which: [H + ] = [OH - ] is neutral [H + ] > [OH - ] is acidic [H + ] < [OH - ] is basic

pH scale ä In any aqueous solution: [H + ] [OH - ] = 1.0 x

pH scale if [H + ] = M then [OH - ] = M the solution is neutral

pH scale if [H + ] = M then [OH - ] = M the solution is acidic

pH scale if [H + ] = M then [OH - ] = M the solution is basic

pH scale pH = negative log 10 [H + ] in moles/liter

pH scale 0147 pH Basic Neutral Acidic [H + ] > [OH - ] [H + ] < [OH - ]

pH scale ä Scale is logarithmic ä Each unit = 10x difference in [H + ]

0147 pH Basic Neutral Acidic pH & Life ä Living cells must maintain an internal pH of 6.5 to 7.5 to survive

pH & Life ä Most biological fluids between pH 6 & pH 8 ä Stomach acid = pH 1.5

Buffers ä Substances which minimize changes in pH ä Blood pH (7.4) maintained by buffers

Buffers ä Ex. Carbonic acid/ bicarbonate ion buffer H 2 CO 3 HCO H + Bicarbonate ion Carbonic acid

Buffers ä Ex. Carbonic acid/ bicarbonate ion buffer OH - + H 2 CO 3 HCO H 2 O if pH increases if pH decreases H + + HCO 3 - H 2 CO 3

Acid Precipitation ä Rain, snow, fog with pH < 5.6 ä Sulfur oxides & nitrogen oxides react with H 2 0 in air ä From burning fossil fuels

Acid Precipitation ä Leaches minerals from soil ä Concentrates toxic minerals (Al) ä Kills trees and aquatic life

Oven cleaner Bleach Ammonia solution Soap Sea water Human blood Pure water Milk Normal rainfall Acid rain Tomato juice Lemon juice Stomach acid Neutral Increasingly Basic Increasingly Acidic

Cl - Water Cl - Na + Water Na +