Chapter02

Chapter02 - BCH 4053Spring 2003Chapter 2 Lecture Notes...

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Chapter 2, page 1 BCH 4053—Spring 2003—Chapter 2 Lecture Notes Slide 1 Chapter 2 Water, pH and Ionic Equilibria Slide 2 Physical Properties of Water • High boiling point • High melting point • High heat of vaporization • High heat of fusion Slide 3 Physical Properties of Water • High specific heat • good heat exchange medium • High surface tension • High dielectric constant • Density of ice < density of liquid • (Ice floats)
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Chapter 2, page 2 Slide 4 Structure of Water • Bent Polar Molecule (Fig 2.1) • Tetrahedral ice structure(Fig 2.2) • hydrogen bonding • Liquid still highly hydrogen bonded • “Flickering Cluster” 10 psec (Fig 2.3) Slide 5 Interaction with Solutes • Solvation of ions (Fig 2.4) • Dielectric constant of water • Hydrogen bonding with polar molecules Slide 6 Interaction with Solutes, (con’t) • Non-polar solutes—“Hydrophobic Effect” • Clathrate “ice-like” structure around non-polar molecule (Fig 2.5) • Water becomes “more ordered”, therefore entropy disfavors solubility • “attraction” between non-polar molecules is really an “expulsion” from water
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Chapter 2, page 3 Slide 7 Interaction with Solutes, (con’t) • Amphipathic molecules (Fig 2.6) • Micelles (Fig 2.7) • Bilayers (Fig 9.2) • lamellar structures (Fig 9.4) • protein folding • base stacking in DNA • Chaotropic Agents • urea and guanidinium ion disrupt ordered structure Slide 8 Interaction with Solutes, (con’t) • Colligative Properties (depends on # of solute particles) • freezing point depression • boiling point elevation • vapor pressure lowering • osmotic pressure increase (Fig 2.8) Slide 9 Acids and Bases • Definition of Acid and Base • Arrhenius—effect on [H + ] • Bronsted-Lowery—proton donor/acceptor • Lewis—electron pair donor/acceptor • The hydrated proton [H 3 O + ] (Fig 2.10)
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Chapter 2, page 4 Slide 10 Auto-ionization of water - 2 23 3 eq 22 2 2 14 w HO + + OH [HO][OH] K = [H O][H O] or H OH [H][OH] K [HO] K [H][OH ] 10 + +- +-- + = == & & Slide 11 Range of [H + ] and [OH - ] • [H 2 O] = 55.5 M • Therefore for Acids [H 3 O + ] << 55.5 M [OH - ] >> 10 -14 /55.5 M • Or for Bases • [OH - ] << 55.5 M • [H 3 O + ] >>10 -14 /55.5 M Slide 12 Definitions of pH and pOH • Because of large concentration range (between about 10 M and 10 -15 M) a logarithmic scale of concentrations is defined: pH = -log[H + ] pOH = -log[OH - ]
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Chapter 2, page 5 Slide 13 Relationship of pH and pOH Since [H + ][OH - ] = 10 -14 -log[H + ] + -log[OH - ] = -log[10 -14 ] pH + pOH = 14 So pH = 14 – pOH and pOH = 14 –pH Neutral solution, pH = pOH = 7 Acid solutions, [H + ] > [OH - ], pH < 7 Basic solutions, [H + ] < [OH - ], pH > 7 (See Table 2.2) Slide 14 Review of Logarithmic Calculations • What is pH if [H + ] is 3.2 x 10 -4 M? 4 log 3.2 x 1 0 log3. 2 log10 0.51(the mantissa ) 4(the characteristic) -3.49 so pH = -(-3.49) = 3.49 - =+ =- = -4 What is [H + ] if pH is 8.56? + p H 8.5 6 0.4 49 9 [H ] 1 0 1 0 1 0 x 10 2.75 x 10 - -- - === = Slide 15 Need Review in such calculations?
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This note was uploaded on 07/22/2011 for the course BCH 4053 taught by Professor Logan during the Spring '06 term at FSU.

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Chapter02 - BCH 4053Spring 2003Chapter 2 Lecture Notes...

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