Chap19 Ionic Equilibria (1)

Chap19 Ionic Equilibria (1) - Chapter 19 Ionic Equilibria...

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Chapter 19 Ionic Equilibria in Aqueous Systems 19-1
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Ionic Equilibria in Aqueous Systems 19.1 Equilibria of Acid-Base Buffers q 19.2 Acid-Base Titration Curves 19.3 Equilibria of Slightly Soluble Ionic Compounds 19.4 Equilibria Involving Complex Ions 19-2
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cid ase Buffers Acid-Base Buffers An acid-base buffer is a solution that lessens the impact of pH from the addition of acid or base. n acid ase buffer usually consists of a onjugate acid An acid-base buffer usually consists of a conjugate acid- base pair where both species are present in appreciable quantities in solution. An acid-base buffer is therefore a solution of a weak acid and its conjugate base, or a weak base and its conjugate acid . 19-3
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Figure 19.1 The effect of adding acid or base to an unbuffered solution. A 100-mL sample of dilute HCl is adjusted to pH 5.00. The addition of 1 mL of strong acid ( left ) or strong base ( right ) changes the pH by several units. 19-4
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Figure 19.2 The effect of adding acid or base to a buffered olution solution. A 100-mL sample of an acetate buffer is djusted to pH 5 00 The addition of 1 mL of strong acid ( left ) or strong base ( right ) changes the pH very ttle adjusted to pH 5.00. little. The acetate buffer is made by mixing 1 M CH 3 COOH ( a weak acid) with H OONa (which provides the conjugate base CH OO - 19-5 1 M CH 3 COONa (which provides the conjugate base, CH 3 COO ).
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uffers and the Common n Effect Buffers and the Common-ion Effect A buffer works through the common-ion effect . Acetic acid in water dissociates slightly to produce some acetate ion: CH 3 COOH (aq ) + H 2 O( l ) CH 3 COO - ( aq ) + H 3 O + ( aq ) acetic acid acetate ion If NaCH 3 COO is added, it provides a source of CH 3 COO - ion, and the equilibrium shifts to the left. CH 3 COO - is common to both solutions. The addition of CH 3 COO - reduces the % dissociation of 19-6 the acid.
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Table 19.1 The Effect of Added Acetate Ion on the Dissociation ab e 9 e ect o dded cetate o o t e ssoc at o of Acetic Acid [CH 3 COOH] init [CH 3 COO - ] added % Dissociation * [H 3 O + ]p H 0.10 0.00 1.3 1.3x10 -3 2.89 0.10 0.050 0.036 3.6x10 -5 4.44 0.10 0.10 0.018 1.8x10 -5 4.74 0.10 0.15 0.012 1.2x10 15 4.92 * % Dissociation = [CH 3 COOH] dissoc x 100 [CH 3 COOH] init 19-7
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ow a Buffer Works How a Buffer Works The buffer components (HA and A - ) are able to consume small amounts of added OH - or H 3 O + by a shift in equilibrium position . CH 3 COOH (aq ) + H 2 O( l ) CH 3 COO - ( aq ) + H 3 O + ( aq ) Added H 3 O + reacts with CH 3 COO - , causing a shift to the left. Added OH - reacts with CH 3 COOH, causing a shift to the right. The shift in equilibrium position absorbs the change in + or [OH - and the pH changes only slightly 19-8 [H 3 O ] or [OH ], and the pH changes only slightly.
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Figure 19.3 How a buffer works. Buffer has equal concentrations of A - and HA. Buffer has more HA after addition of H 3 O + . Buffer has more A - after addition of OH - . H 3 O + OH - +CH OOH H + CH OO - H OOH + OH - CH OO - H 19-9 H 2 O + CH 3 COOH 3 O + CH 3 COO CH 3 COOH + OH 3 COO + H 2 O
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elative Concentrations of Buffer Components Relative Concentrations of Buffer Components CH 3 COOH (aq ) + H 2 O( l ) CH 3 COO - ( aq ) + H 3 O + ( aq ) K a = [CH 3 COO - ][H 3 O + ] [CH 3 COOH] [H 3 O + ] = K a x [CH 3 COOH] [CH 3 COO - ] Since K a is constant, the [H 3 O +
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Chap19 Ionic Equilibria (1) - Chapter 19 Ionic Equilibria...

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