241section2-10-6A

241section2-10-6A - Chem 241 Summer 2010 Acid/Base...

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Chem 241 –Summer 2010 1 Acid/Base Definitions Arrhenius Acid - provides H + in H 2 O Arrhenius Base - provides OH - in H 2 O Bronsted Acid - H + donor + Bronsted Base - H acceptor Lewis Acid - e - acceptor Lewis Base - e - donor HCl + H 2 O H 3 O + + Cl - HCl - acid H O b Acid/Base Definitions H 2 O - base H 3 O + - conjugate acid Cl - - conjugate base Acid/Base Definitions NH 3 + H 2 O NH 4 + + OH - NH 3 -base H O acid H 2 O - NH 4 + - conjugate acid OH - - conjugate base Acid/Base Definitions H 2 O is amphiprotic - can be an acid or base Autoprotolysis dissociation Autoprotolysis - dissociation into both and acid and base Acid/Base Definitions Autoprotolysis 2 H 2 O H 3 O + + OH - (H O H + +OH (H 2 O + OH - ) K w = [ H 3 O + ][OH - ] = 10 -14 (at “room” temperature) Acid/Base Definitions Other solvents can undergo Autoprotolysis 2CH 3 OH CH 3 OH 2 + + CH 3 O - K=2 10 -17
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Chem 241 –Summer 2010 2 Acid/Base Definitions solvents ti ti aprotic (CH 3 CN) protic protogenic (acids) intermediate (H 2 O) protophilic (bases) Acid/Base Definitions K a is the “acid dissociation” constant - i.e. the equilibrium constant K is the “base hydrolysis constant” K b is the base hydrolysis constant Strong Acids »completely dissociate HC +H O H O + + C - Acid/Base Definitions HCl + H 2 O H 3 O + Cl 0 ] [ HCl ] [ ] ][ [ 3 HCl Cl O H K a Acid/Base Definitions Strong Bases »completely dissociate KOH K + +OH - KOH K + OH [] KOH 0 ] [ ] ][ [ KOH OH K K b Acid/Base Definitions Weak Acids »DO NOT completely dissociate CH 3 CO H H + + CH CO 2 - 2 3 CH CO H 32 0 ] [ ] ][ [ 2 3 2 3 H CO CH CO CH H K a Acid/Base Definitions (K a values in Appendix G)
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Chem 241 –Summer 2010 3 Acid/Base Definitions 1.1x10 -3 2.9x10 -5 Acid/Base Definitions Weak Bases »DO NOT completely associate NH 3 + H 2 O NH 4 + + OH - [] NH 3 0 ] [ ] ][ [ 3 4 NH OH NH K b Acid/Base Definitions Generic reactions - acids HA+ H 2 O H 3 O + + A - HA H + +A - HA H + A ] [ ] ][ [ HA A H K a Acid/Base Definitions Generic reactions - bases B + H 2 O BH + + OH - A - +H 2 O HA + OH - A + H O ] [ ] ][ [ ] [ ] ][ [ A OH HA K B OH BH K b b Equilibrium constant is a function of chemical activity Activity Coefficients A + B C + D at “low” concentration chemical activity = concentration B A D C B A D C B A D C K ] [ ] [ ] [ ] [ T T T T pH and pK a pH = -log [H + ] pOH = -log [OH - ] pK a = - log K a pK b = - log K b
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Chem 241 –Summer 2010 4 pH and pK a pOH = -log[OH - ] pH + pOH = -log[H + ] + -log[OH - ] = -log[H + ][OH - ] = -log K w = pK w = 14 pH + pOH = 14 pH and pK a HA H + + A - K a A - + H 2 O HA + OH - K b ] [ ] ][ [ ] [ ] ][ [ A HA OH HA A H K a K b = K a K b = [H + ][OH - ] = K w Calculation - Strong Acids two regimes to consider » high concentration » low concentration Calculation - Strong Acids high concentration » e.g. 0.010M HCl HCl + + Cl - K = a [H + ] = 0.010 pH = 2.00 Calculation - Strong Acids low concentration » e.g. 1.0 x 10 -8 M HCl » [H + ] = 1.0 x 10 -8 ?
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This note was uploaded on 03/14/2011 for the course CHEM 241 taught by Professor Tiani during the Spring '08 term at UNC.

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241section2-10-6A - Chem 241 Summer 2010 Acid/Base...

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