Lecture 3,4 - Lectures 3,4 Water and pH Water is essential...

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Lectures 3,4 Water and pH Water is essential for life; and it has unusual physical properties related to the weak forces that connect atoms covalent: strong (142 –O:O- to 946 N:::N, -C:C- 343 kJ/mol; 0.15 nm) hydrogen: weak (12-30 kJ/mol ; 0.3 nm; combine two electronegative atoms, O,N, e.g. H ... O-H: water, note 10-ps “flickering clusters”) ionic: moderate (20 kJ/mol ; 0.25 nm in crystal; but moderated by H 2 O: F = Q 1 Q 2 / ε r 2 and ε [dielectric constant] = 1 in vacuum, 80 in H 2 O) Vanderwaal’s: weak (0.4-4.0 kJ/mol ; 0.1 nm) hydrophobic: moderate (<40 kJ/mol; depend on hydrocarbons disrupting the H-bonds “flickering clusters” of H 2 O) Dissociation of H-O bonds in water H 2 O + H 2 O H 3 O + + OH - [H 3 O + ] = [OH - ] = 10 -7 in pure H 2 O as with hydrogen bonds, note “flickering” as H is traded around H 2 O molecules Note the convention: H 2 O H + + OH - and [H 3 O + ] = [H + ] K eq = [H + ][OH - ]/[H 2 O] Because [H 2 O] is approx. constant, define K w = K eq *[H 2 O] K w = [H + ][OH - ] = (10 -7 )( 10 -7 ) = 10 -14 M 2 Define the p function: p(X) = - log
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Lecture 3,4 - Lectures 3,4 Water and pH Water is essential...

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