1M_05_WeakAcid - 1 Weak Acids: Titration Curves, Buffers,...

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Unformatted text preview: 1 Weak Acids: Titration Curves, Buffers, and the Henderson- Hasselbach Equation Experiment 5 #5 Weak Acids: Titration Curves, Buffers, and the Henderson-Hasselbach Equation Goal: s Use titration pH curve and melting point to identify an unknown weak organic acid Method: s Find n acid , MM acid , K a and from titration of acid solution s Find melting point range of solid acid from melting point experiments 2 Acid-Base Definitions Acids s generate H + in water s H + donors s excess H + Bases s generate OH- in water s H + acceptors s Excess OH- Equilibrium in Water 14 25 3 10 1- + + × = = = = o @-- w eq ] ][OH [H ] ][OH O [H K K Small K ≡ equilibrium favors reactants 3 As [H + ] rises, [OH- ] falls H + H + H + OH- OH- OH- 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Acidic Neutral Basic H + and pH [H + ] 1 × 10 to 1 × 10-14 in water pH 1 to 14 in water 14 10 1- + × = = ] ][OH [H K- w ] [OH K ] [H- w = + ] [H- pH + = log 4 Relationships H + OH- [H + ] >[OH- ] Acidic solution Basic solution [H + ] =[OH- ] [H + ] <[OH- ] Neutral solution H 2 O pH < 7 pH > 7 pH = 7 5 Strong Acids (exp. 4) 100% dissociation / good H + donor equilibrium lies far to right HA → H + + A- HCl H + Cl- HCl H + Cl- Relative # moles Before dissociation After dissociation 6 Weak Acids (exp. 5) <100% dissociation / not-as-good H + donor equilibrium lies far to left HA H + + A- HA H + A- Relative # moles Before dissociation After...
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1M_05_WeakAcid - 1 Weak Acids: Titration Curves, Buffers,...

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