water - Properties of Water Properties Polarity...

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Unformatted text preview: Properties of Water Properties Polarity Temperature-Stabilizing Cohesive Solvent Water Is a Polar Covalent Molecule Covalent Molecule Molecule has no net charge charge Oxygen Oxygen end has a slight negative charge slight Hydrogen Hydrogen end has a slight positive charge slight O H H Hydrogen Bonding Hydrogen Molecule Molecule held together by polar covalent bonds has no NET charge However, However, atoms of the molecule carry different charges different Atom Atom in one polar covalent molecule can be attracted to oppositely charged atom in another such molecule another Liquid Water H+ + + _ O H H+ + _ O H + Examples of Hydrogen Bonds one large molecule another large molecule a large molecule twisted back on itself Fig. 2.12, p. 27 Hydrophilic & Hydrophobic Hydrophilic Substances Hydrophilic substances Polar Hydrogen Hydrogen bond with water Example: sugar Hydrophobic substances Nonpolar Repelled by water Example: oil Temperature-Stabilizing Effects Temperature-Stabilizing Liquid Liquid water can absorb much heat before its temperature rises before Why? Why? Much Much of the added energy disrupts hydrogen bonding rather than increasing the movement of molecules increasing Evaporation of Water Evaporation Large Large energy input can cause individual molecules of water to break free into air molecules As As molecules break free, they carry away some energy (lower temperature) some Evaporative Evaporative water loss is used by mammals to lower body temperature mammals Why Ice Floats Why In In ice, hydrogen bonds lock molecules in a lattice Water Water molecules in lattice are spaced farther apart then those in liquid water farther Ice is less dense than water Water Cohesion Water Hydrogen Hydrogen bonding holds molecules in liquid water together together Creates Creates Allows Allows surface tension water to move as continuous column upward through stems of plants plants Water Is a Good Solvent Water Ions Ions and polar molecules dissolve easily in water When When solute dissolves, water molecules cluster around its ions or molecules and keep them separated keep Spheres of Hydration – + + + + – Na+ – – – – – – – – – + + + + + Cl– + + + + + + + + + Fig. 2.16, p. 29 Hydrogen Ions: H Hydrogen + Unbound protons Have important biological effects Form when water ionizes The pH Scale The Measures H+ concentration of fluid Change of 1 on scale means 10X change Change in H+ concentration in Highest H+ Lowest H+ 0---------------------7-------------------14 Acidic Neutral Basic Examples of pH Examples Pure Pure water is neutral with pH of 7.0 Acidic Stomach Lemon acid: pH 1.0 - 3.0 juice: pH 2.3 Basic Seawater: Baking pH 7.8 - 8.3 soda: pH 9.0 Acids & Bases Acids Acids Donate Acidic H+ when dissolved in water solutions have pH < 7 Bases Accept Acidic H+ when dissolved in water solutions have pH > 7 Weak and Strong Acids Weak Weak acids Reluctant Can H+ donors also accept H after giving it up Carbonic Strong acid (H2CO3) is example acids Completely give up H+ when dissolved Hydrochloric acid (HCl) is example Buffer Systems Buffer Minimize shifts in pH Partnership Partnership between weak acid and base it forms when dissolved it Two work as pair to counter shifts in pH Carbonic Acid-Bicarbonate Buffer System Buffer When When blood pH rises, carbonic acid dissociates to form bicarbonate and H+ dissociates H2C03 -----> HC03- + H+ When When blood pH drops, bicarbonate binds H+ to form carbonic acid HC03- + H+ -----> H2C03 Salts Salts Compounds Compounds that release ions other than H+ and OH- when dissolved in water Example: Many Many NaCl releases Na+ and Cl– salts dissolve into ions that play important biological roles ...
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This note was uploaded on 10/12/2011 for the course BIO 101 taught by Professor Martin during the Spring '08 term at Rutgers.

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