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2 - Test 2 Water pH Special Qualities of Water Only...

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Test 2- Water & pH Special Qualities of Water - Only substance to exist in the natural environment in all 3 physical states (solid, liquid, gas) - Water is most dense at 4 degrees C - Polarity - Hydrogen bonds - Cohesion & Adhesion - Ability to moderate temperature - Expansion upon freezing - Versatility as a solvent Polar Molecule - Two ends of a molecule have opposite charges Water as a Polar Molecule - Contains 2 Hs covalently bonded to an O, but O is more electronegative than H (O is slightly -, H slightly +) = polar covalent bonds - H is attracted to the O of another water molecule (forming H-bond) Hydrogen Bonds in Water - Liquid: *H-bonds are fragile & weak *Constantly forming, breaking & reforming - Solid: *Water becomes locked in a crystalline lattice *Each water molecule is H-bonded to 4 others *H-bonds keep molecules an “arm’s length” apart (far enough apart of make ice 10% less dense than water) Cohesion - H-bonds hold water molecules together - Contributes to the transport of water & dissolved nutrients against gravity in plants Adhesion - The clinging of one substance to another - Adhesion of water to cell walls by H-bonds helps counter the downward pull of gravity Surface Tension - A measure of how difficult it is to stretch or break the surface of a liquid
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- At the surface of water, the molecules are H-bonded to each other & the molecules below them, forming an invisible film Moderation of Temperature - Water moderates temperature by absorbing heat from air that is warmer and releasing the stored heat into cooler air - It can absorb or release lots of heat without dramatically changing its temperature Kinetic Energy - Energy of motion - The faster an object moves, the higher the kinetic energy Heat - Measure of the matter’s total kinetic energy due to motion of its molecules - Depends on the matter’s volume - Heat passes from the warmer object to the cooler object until the two are equal Temperature - Average kinetic energy - Regardless of volume Calorie (cal) - The amount of heat it takes to raise 1 gram of water 1 degree C - Also amount of heat that 1g of water releases when it cools by 1 degree C Kilocalorie (kcal)
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