Chapter 3 Concept 3 1 Polar covalent bonds in water molecules result in hydrogen bonding Water is a polar molecule Polarity allows water molecules to form hydrogen bonds with each other Concept 3 2 Four emergent properties of water contribute to Earth s suitability for life 1 Cohesive behavior 2 Ability to moderate temperature 3 Expansion upon Freezing 4 Versatility as a solvent Cohesion of water molecules Cohesion Hydrogen bonds holding water molecules together Adhesion Attraction between different forces Surface tension Measure of how hard it is to break the surface of a liquid Related to cohesion Moderation of temperature by water Absorbs heat Water can act to minimize temperature changes Water can release energy with only a slight change in its temperature Heat and temperature motion water by 1 degree Celsius Kinetic Energy is the energy of motion Heat is a measure of the total amount of kinetic energy die to molecular Calorie Cal amount of heat required to raise the temperature of 1 gram of Kilocalories kcal where 1kcal 1 000 Cal Also the calories on the food Joule j is another unit of energy where 1 J 239 Cal or 1 Cal 4 184 J Water s high Specific Heat Specific heat of a substance is the amount of heat that must be gained or lost for 1g of that substance to change by 1 degree Celsius Water s specific heat is 1 Cal G C Has a high specific heat due to hydrogen bonds it minimizes temperature fluctuations to allow life Evaporative Cooling Liquid to gas Heat of vaporization is how a liquid converts to a gas Water requires 580 Cal g at 25 degrees Celsius bodies of water Evaporative cooling of water stabilizes temperatures in organisms and Ice Solvent Water is at it s greatest density at 4 degrees Celsius Ice floats because its molecules are more ordered than its liquid form By being less dense it floats protecting organisms around it Water as a solvent dissolves polar molecules Not universal solvent When it acts as a solvent it creates a hydration cell around the ions Hydrophilic Hydrophobic Hydrophilic compounds will dissolve in water Colloids are fine suspensions in water Cotton although it can dissolve wont because it is to big of a molecule Hydrophobic compounds will not dissolve in water Most biological chemical reactions occur in aqueous solutions Concept 3 3 Acid Base affects living organisms 2H2O H3O OH Hydronium H OH Hydroxide Rate is constant for disassociation and re association Concept 3 3 Acid Base effect living organisms Acid has high H and low OH Base has low H and high OH pH Scale At 25 degrees Celsius H and OH H OH 10 14 pH of a solution is determined by pH log H For a neutral solution H is 10 7 pH 7 7 Most biofluids have between 6 to 8 pH Buffers Minimize changes in pH
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