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Chapter 3: Water is BEAST

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Marlene Michalek

on 15 September 2010

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Transcript of Chapter 3: Water is BEAST

Chapter 3:
Water is BEAST High Heat of Vaporization Expansion upon freezing Water- It's a Fact!!! Water is... Awesome!!! Hydrogen Bonds charged regions of a polar molecule are attracted to oppositely charged parts of neighboring molecules each molecule can hydrogen-bond to multiple partners each water molecule forms a maximum of 4 hydrogen bonds with neighboring water molecules these associations are constantly changing Water and It's Awesome Properties Cohesive Behavior High Specific
Heat Versatile Solvent cohesion: the ability of a substance to stick to itself -due to hydrogen bonding -contributes to upward transport
of H20 against gravity in plants adhesion: the ability of a substance to stick to other substances also plays a role in transport of H20 in plants against gravity Surface tension: measure of how difficult it is to stretch or break the surface of a liquid Amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1 degree Celsius Specific Heat of Water: 1 calorie per gram per degree Celsius or (1 cal/g/oC) Think of specific heat as a measure of how well a substance resists changing temperature when it absorbs or releases heat -due to hydrogen bondng Heat must be absorbed to break hydrogen bonds and is released when hydrogen bonds form Important because: - Large bodies of water act as “heat sinks” absorb heat from the sun during daylight & summer while warming up only a few degrees - At night & winter the gradually cooling water can warm the air - Also tends to stabilize ocean temperatures quantity of heat a liquid must absorb for 1 gram to be converted to the gaseous state conversion of water into vapor requires breaking of H-bonds High heat of water vaporization - to evaporate 1 gram of H2O at 25oC about 540 cal/gram is needed helps moderate Earth's climate evaporative cooling: hottest molecules (have more kinetic energy) leave as a gas leaving cooler water behind contributes to the stability of temperatures in lakes and ponds provides a mechanism that prevents animals from overheating (sweat) densest at 4 degrees C contracts as it cools to 4 degrees C expands (becomes less dense) as it cools from 4 degrees C to 0 degrees C oceans and lakes don't freeze solid because ice floats (water density) because of H-bonding, water is less dense as a solid than it is as a liquid (which makes ice float) - Exotic Behavior Water... does not have enough kinetic energy to break H-bonds as it is freezing as temp falls to 0 degrees C, water becomes locked into a crystalline form, each H2O molecule forms a max of 4 H-bonds, whick keeps each molecule farther apart than they would at a liquid state This benefits life because: 1. If ice sank, eventually all ponds, lakes and even the ocean would freeze solid...making life in water impossible 2. Floating ice insulates the liquid water below it...allowing life to exist...and ROCK!!! due to the polarity of water hydration spheres form (a sphere of water molecules) that surrounds each solute ion in an aqueous solution Hydrophilic: property of having an affinity for water Hydrophobic: property of not having an affinity for water, and not being water soluble ionic and polar substances are hydrophillic, but nonpolar compounds are hydrophobic Dissociation of Water Molecules an H atom participating in an H-bond between 2 H2O molecules can occasionally shift from one molecule to the other acid substance that increases the hydrogen ion concentration of a solution base substance tht reduces the hydrogen ion concentration of a solution pH and Buffers Living cells are 70-95% water Water covers about 75% of the earth Life on earth probably evolved in water Water exists naturally in 3 physical states- solid, liquid and gas water has several properties from its molecular structure and molecular interactions Water is a polar molecule Oxygen is more electronegative that hydrogen polar bonds and asymmetrical shape give water molecules opposite charges on opposite sides has a distinct V shape, with a slight positive charge on each hydrogen atom ph = 7 is a neutral solution ph < 7 is an acidic solution pH >7 is a basic solution Buffers substance that prevents large sudden changes in pH -by minimizing wide fluctuations in pH, buffers help organism maintain the pH of the body fluids within a narrow range (usually 6-8) required for life -works by accepting hydrogen ions from the solution when they are in excess & donating hydrogen ions to the solutions when they are depleted usually contains a weak acid and its corresponding base Example: (Bicarbonate Buffer) Acid Precipitation: rain, snow, or fog with a pH lower (more acidic) than 5.6

-can damage lakes and streams
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