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Water and Mixtures

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BIOL 1117
Christopher Richardson

L4 -The Chemistry of Life: Water and Mixtures 9/11/13 • Mixtures: substances are physically blended, but not chemically combined • Most mixtures in our bodies consist of chemicals dissolved in water • First, water atoms are joined by polar covalent bonds • Second, those bonds are arranged in a non-balanced form • Water o Water molecule is polar and forms hydrogen bonds. o Water’s polarity creates a set of properties that account for its ability to support life.  solvency  cohesion  adhesion  chemical reactivity  thermal stability o Solvency  Solvency: ability to dissolve other chemicals  Water is called the universal solvent • Hydrophilic: substances that dissolve in water • Hydrophobic: substances that do not dissolve in water  Water as a solvent • Amolecule must be polarized or charged (ionic compounds are charged) in order to be dissolved in water • Hydration spheres are multiple arrangements of water molecules that are attracted to an ion (prevent bonding of ions) • Most energetically stable arrangement • Ionic bonds are broken by the energy released from the formation of hydration spheres o Adhesion and Cohesion  Adhesion: tendency of one substance to stick to another  Water adheres to other substances such as tissues in body and forms a lubricating film  Cohesion: tendency of molecules of same substance to stick to each other • water is very cohesive due to its hydrogen bonds • surface film on surface of water is due to molecules being held together by a force called surface tension o Chemical Reactivity of Water  Ability to participat+ in chem-cal reactions  Water ionizes into H and OH  Water ionizes other chemicals (acids and salts)  Water is involved in hydrolysis and dehydration synthesis reactions • Hydrolysis: the splitting of a water molecule as a chemical breaks up a macromolecule • Dehydration synthesis reaction: the forming of a water molecule as a macromolecule is created o Thermal Stability of Water  Heat capacity: the amount of heat required to raise the temperature of 1 g of a substance by 1 degree C. • Water has a high heat capacity • Can absorb a lot of energy without changing temperature or state. • High heat capacity because the absorbed energy is used to push apart the H bonds (to oppose the H bonds) before water molecules can be physically pushed farther apart; only when the H bonds are opposed can water molecules separate more and the temperature of water is raised • Water’s high heat capacity gives it thermal stability: means certain amount of energy is absorbed by water in the body which stabilizes internal body temperature • Effective coolant: because water can absorb a lot of heat, it can carry away heat energy as it evaporates • Mixtures in Water o Asolution consists of particles of matter called a solute mixed with a more abundant substance, usually water, called a solvent.  Solute particles will pass through most selectively permeable membranes. When the solution stands, the solutes do no sepa
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