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IUB BIOL-L 112 - The Unique Properties of Water

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BIOL-L 112 1nd Edition Lecture 2 Outline of Last Lecture I. Water’s Role in LifeA. Electronegativity and the Difference Between Polar and Nonpolar MoleculesII. Water’s Ability to Form Hydrogen BondsIII. Four Emergent Properties of WaterA. Water is CohesiveB. Water Moderates TemperatureOutline of Current Lecture I. Four Emergent Properties of Water (Continued) a. Water Expands Upon Freezingb. Water is a Versatile SolventII. Acids and BasesCurrent LectureI. Water has four unique properties because of hydrogen bonding that make life possible. A. The third unique property of water is the fact that it expands upon freezing. In liquid water, the hydrogen bonds are unstable and change arrangement causing the molecules to be closer together. In a solid crystal of ice, each water molecule is in a fixed structure with other water molecules around it and is 10% less dense than liquid water. Ice floats on water because it is less dense, which allows life to exist under frozen surfaces. B. The fourth property of water is its versatility as a solvent (dissolving agent). Because water is a polar molecule and forms hydrogen bonds easily, it forms a hydration shell. It is even able to dissolve large protein molecules if it has many ionic and polar regions present. Definitions: - Hydration shell: A sphere of water molecules that surround a substance when it is dissolved in water. - Hydrophilic: Has affinity for water- Hydrophobic: Does not have affinity for water (repels water)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.C. Acidic and basic conditions affect living organisms. For example, the lumen of thestomach is very acidic with a pH of 2. The function of the acid in the stomach is to denature proteins and kill microorganisms. Acidic and basic conditions modify the H+ and OH- concentrations in a solution. An acid serves to increase the protonconcentration, while a base serves to reduce the proton concentration in a solution. In order to describe the acidity or basicity of a solution, biologists use the pH scale. - Buffers are used to keep the pH of a solution from fluctuating. They contain both a weak acid and its corresponding weak base. If the pH of a substance increases, the buffer will act to maintain homeostasis by reacting to lower the H+ concentration (alkalosis). If the pH of a substance drops, the buffer will maintain homeostasis by reacting to increase the H+ concentration and raise the pH (acidosis). Helpful formulas:- [H+][OH-]=10-14- pH of a solution=


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IUB BIOL-L 112 - The Unique Properties of Water

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