Bio Lecture 4 - Lecture 4 Guide August 31...

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Lecture 4 Guide August 31 See EXAM 1 READINGS, Chapter 3 (Moodle), Water – (H 2 O) Biological Importance a. Living cells are 70-95% H 2 O b.Solvent for biological reactions c. 71% of the earth’s surface is covered by water Water molecule Polar covalent bonds Hydrogen bonds between water molecules – produces cohesion Some Important Properties Of H 2 O a. High specific heat – 1 cal/g/ ° C (stabilizes temperatures) b. High heat of vaporization – 580 cal/g  (produces evaporative cooling) c. Maximum density at 4 ° C (ecological importance for organisms living in  aquatic habitats)  
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Solutions  - a homogeneous mixture consisting of a solvent , and a solute(s) Water is an excellent solvent for ionic  or polar  molecules (see Figs. 3.6 and  3.7) Solute Concentration in Aqueous Solutions Concentration  = mass (weight)/ volume a.  In reactions, molecules combine by number b. A mole of any compound possesses 6.02 X 10^23 c.Molarity(concentration) – moles per liter of solution (mol/liter) Mole (mol) - sum of the atomic weights (mass numbers) in daltons (= grams) Examples: Molecule                         grams/mol H 2 O (2+16)                      ~18 NaCl (23+35) ~58 Sucrose (C 12 H 22 O 11 ) (144+22+176)       ~342   Calculating Molarity - molar concentration (mol / L)  
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