Lecture Two - Water pH buffers

Lecture Two - Water pH buffers - What chemical properties...

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What chemical properties contribute to water's uniqueness? Polarity and H - bonding a) leads to hydrogen bonding b) contribute to its uniqueness Reversible ionization a) dissociation of water is an equilibrium reaction b) equilibrium can be shifted in one direction or another c) for an equilibrium reaction there will be an equilibrium constant associated with it d) the higher the equilibrium constant, the higher tendency for the reaction to go to completion Water, pH, buffers (Lecture Outline) water: common but so unique a) chemical properties that contribute to its uniqueness pH a) definition of pH b) ionization of water as the basis for pH scale c) equilibrium reactions d) Henderson-Hasselbalch equation e) Titration curves and pK a buffers a) definition b) how do they work? c) what determines their effectiveness d) importance of buffers in physiology; consequences of failure in regulation I. Water undergoes reversible ionization: H 2 O ←→ H + + OH - (The dissociation of water) Equilibrium constant (K eq ) = [H + ][OH - ] = 1.8 x 10 -16 [H 2 O] This small value of K eq inicates that the actual number of dissociated molecules is very small relative to the number of undissociated. Thus the concentration of H 2 O is unchanged. The equation becomes: K eq = 1.8 x 10 -16 = [H + ][OH - ] [55.5M] [55.5M][1.8 x 10 -16 ] = [H + ][OH - ] 1 x 10 -14 M 2 = [H + ][OH - ] The ion product of water, K w , is a constant K w = 1 x 10 -14 = [H + ][OH - ] This property of water is central to its role as a biological solvent.
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II. The pH scale is derived from the ionization of water 1 x 10 -14 = [H + ][OH - ] pH is defined as - log[H + ] pH ranges from 0 - 14 Note that the pH scale is logarithmic - a difference of 1 pH unit means that a solution has 10X [H + ] than the other Why are we concerned about pH in biological systems? III. Metabolism produces changes in [H
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Lecture Two - Water pH buffers - What chemical properties...

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