1. W ATER : S OLVENT OF L IFE Chapter 3

2. o ¾’s of the Earth is covered in water o Only substance that exists naturally in all 3 states of matter o Water makes up the majority of all organisms o Water is fundamental for the survival of all living organisms o 66% of body weight o Maintains internal temperature o Cells are 70-95% water o Blood is 55% plasma, 92% of which is water Why is Water so Important?

3. W ATER I S A P OLAR C OVALENT M OLECULE What makes it polar? Molecule has no net charge Oxygen end has a slight negative charge Hydrogen end has a slight positive charge Charged ends attract oppositely charged ends of other molecules Represents the electronegativity, pull on the electrons, by oxygen

4. ‘O PPOSITES ATTRACT ’ Hydrogen bonds form between molecules of water Slightly positive hydrogen is attracted to slightly negative oxygen As a liquid, the bonds are weak Break and reform readily Many molecules so there are always bonds

5. P ROPERTIES OF W ATER Cohesive and adhesive forces Temperature moderation States of matter Solvent of life Each property leads to the emergent properties that make water so beneficial

6. W ATER C OHESION Hydrogen bonding holds molecules in liquid water together Constantly changing, but ordered Allows water to move as continuous column upward through stems of plants Adhesion : H bonds with other substances to counter gravity Surface tension difficulty to break water surface Air and water H-bonded to create a ‘film’ ‘Belly flop’ Overfilling glassware

7. H EAT AND T EMPERATURE Kinetic energy : energy of motion Heat is a measure of the total kinetic energy created by moving matter Temperature is the intensity of heat (average KE) Heat moves from warmer to cooler objects until equilibrium is reached Ice cools drinks by absorbing heat, thus ice melts Celsius scale indicates temperature 0ºC freeze, 100ºC boil, 37ºC body, 20-25ºC room temp. Calorie : amount of heat needed to raise temperature of 1g of water 1°C Kilocalorie raises 1 kg by 1°C = calories on food pkgs

8. S PECIFIC H EAT Amount of heat that must be lost or absorbed to change 1g of a substance by 1°C This is higher than most substances Explains why water is resistant to temperature change Absorbing heat breaks H bonds Heat is released when H bonds form H bonds must be broke before molecules can move faster = increase temp Coastal effects Oceans absorb heat during day and releases at night to warm air

9. C HANGES OF S TATE Evaporation : liquid to gas Increased rate as KE increases Heat of vaporization : amount of heat that must be absorbed to convert 1g of liquid to gas H bonds must be broken for this to occur Steam burns occur as gas is converted to liquid on the skin Evaporative cooling : as liquid evaporates, the remaining surface cools Molecules with the hottest (highest KE) are first to leave Prevents overheating of life High humidity prevents evaporative cooling

10. I CE Ice floats because it is less dense than water 4°C water is most dense, above water behaves like a liquid (expand as warmed) As temps drop below 4°C, the movement of molecules slows and fewer H bonds are broken Water molecules expand at 0°C

11. W ATER AS A V ERSATILE S OLVENT Solution : homogeneuos liquid mix of 2+ substances Solvent : dissolving agent Aqueous solution when water is solvent Solute : substance that is dissolved Key is polarity ‘Like dissolves like’

12. H YDROPHILIC & H YDROPHOBIC S UBSTANCES Hydrophilic substances Polar or ionic Hydrogen bond with water Example: sugar, vinegar Hydrophobic substances Nonpolar or nonionic Repelled by water Example: oil, cell membranes

13. D ISSOCIATION OF W ATER Hydrogen atoms shift between molecules, leaving the electron behind H + ( hydrogen ion ) leaves to form H 3 O + ( hydronium ion ), OH - ( hydroxide ion ) stays Releases equal amounts with each reaction Neutral on pH scale at 7.0

14. A CIDS & B ASES Acids Donate H + when dissolved in water HCl H + +Cl - Proton donors Acidic solutions have pH < 7 Bases Release -OH when dissolved in water NaOH Na + +OH - Proton acceptors Basic solutions have pH > 7

15. The pH Scale

16. T HE P H S CALE Measures H + concentration of fluid Negative logarithmic scale Change of 1 on scale means 10X change in H + concentration Highest H + Lowest H + 0---------------------7-------------------14 Acidic Neutral Basic

17. B UFFER S YSTEMS Minimize shifts in pH Many created within the body Human blood at 7.4, can’t survive change to 7 or 7.8 Accept H + when in excess and donate when not Partnership between a weak acid and weak base

18. A CID R AIN Rain with an elevated pH Result of burning fossil fuels Damage to aquatic and terrestrial environments