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Acid-Base Equilibrium Chapter 18
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Acids and Bases Arrhenius acids:generate H + in water bases:generate OH - in water Brønsted-Lowry acids:H + donors bases:H + acceptors HCl + H 2 O Cl + H 3 O + acid base acid base
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H 3 O + = H + (aq) = proton in water
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Conjugate acid-base pairs Conjugate base: remains after H + is lost acid: HClconj. base:Cl - Conjugate acid: remains after H + is gained base: NH 3 conj. acid:NH 4 + BaseAcid+ Base+ Conjugate Pair
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Strong and Weak Acids Strong:100% dissociation good H + donor equilibrium lies far to right (HNO 3 ) generates weak base (NO 3 - ) Weak:<100% dissociation not-as-good H + donor equilibrium lies far to left (CH 3 COOH) generates strong base (CH 3 COO - )
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Very strong Strong Weak Very weak Relative Acid Strength Relative Conj. Base Strength Very weak Weak Strong Very strong
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Acid Dissociation Constant
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K a Increases Strength vs. K a
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Acid Base Conj. Acid Conj. Base Acid Base Conj. Acid Conj. Base Water is amphoteric
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Proton Transfer in Water OH H OH H OH H OH H OH H O H H OH H OH H + - OH H O H - H OH H OH H
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[H 3 O + ] and [OH - ] [H 3 O + ] 1x10 0 to 1x10 -14 in water [OH - ] 1x10 -14 to 1x10 0 in water
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Finding [H 3 O + ] and [OH - ]
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pH Scale pH 0 to 14 in water pOH 14 to 0 in water pK w = pH + pOH = 14
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H+H+ H+H+ H+H+ OH - 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Acidic Neutral Basic pH and pOH As [H 3 O + ] rises, [OH - ] falls As pH falls, pOH rises
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Indicators
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Polyprotic Acids 1.H 3 PO 4 H 2 PO 4 - + H + K a1 = 7.2 x 10 -3 2.H 2 PO 4 - HPO 4 2- + H + K a2 = 6.3 x 10 -8 3.HPO 4 2- PO 4 3- + H + K a3 = 4.2 x 10 -13 K a1 > K a2 > K a3
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Strength of Bases Strong: 100% dissociation OH - supplied to solution NaOH (s) Na + (aq) + OH - (aq) Weak: <100% dissociation OH - by reaction with water CH 3 NH 2(aq) + H 2 O (l) CH 3 NH 2(aq) + OH - (aq)
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Base Dissociation Constant
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K w, K a and K b
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Structure and Acid-Base Behavior Binary hydrides: 1.Bond polarity (high acid strength) 2.Bond strength (low acid strength)
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Structure and Acid-Base Behavior Binary oxides: 1.Acidic oxides (acid anhydrides) O—X bond:strong and polar SO 2, SO 3, NO 2, P 4 O 10, … 2.Basic oxides (basic anhydrides) O—X bond:ionic K 2 O, CaO, …
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Structure and Acid-Base Behavior Oxoacids (H a X b O c ): 1.Same number of O on different X EN of X 2.Different number of O on same X more O
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Relative Strengths of Oxoacids
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Cl OH Electron density ClOH Electron density O ClOH Electron density O O ClOH Electron density O O O 1 O 2 O 3 O 4 O Increasing Acid Strength
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Lewis Acids and Bases Lewis Acid: electron pair acceptor Lewis Base: electron pair donor Acid Base
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