Chapter16_LEC - Chapter 16 Aqueous Ionic Equilibrium...

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Chapter 16 Aqueous Ionic Equilibrium
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Tro, Chemistry: A Molecular Approach 2 Buffers buffers are solutions that resist changes in pH when an acid or base is added Neutralize added acid or base How to make buffer solution: 1. Mix a solution of a weak acid & salt containing its conjugate base anion, CH 3 3 COONa) ( weak acid/conj.base) 2. Mix a weak base, (B:), & soluble salt of its conjugate acid, H:B + Cl ( NH 3 in NH 4 Cl) ( weak base/conj.acid ) H 2 O ( l ) + NH 3 ( aq ) NH 4 + ( aq ) + OH
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Tro, Chemistry: A Molecular Approach 3 How Buffers Work HA ( aq ) + H 2 O ( l ) A ( aq ) + H 3 O + ( aq ) work by applying Le Châtelier’s Principle to weak acid equilibrium When you add base: weak acid molecules, HA – react with added base to neutralize it ( H 3 O + combine with OH to make H 2 O; & shift the equilibrium to right When you add acid: conjugate base anion, A - combine with added acid H + to make more HA (unionized) and keep the H 3 O + constant
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Tro, Chemistry: A Molecular Approach 4 If OH - is added to an equimolar solution of HF in NaF, the reacts with the OH to make F and water. If acid is added, the F reacts to form HF (unionized) and water.
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Tro, Chemistry: A Molecular Approach 5 Buffer Calculations equilibrium constant expression for the dissociation of a generic acid, HA p K a pH acid base
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Tro, Chemistry: A Molecular Approach 6 p K = pH − log [base] [acid] pH = p K + log [base] [acid] Henderson–Hasselbalch equation , is used to find the pH of a solution, Works good for weak acid & the initial concentrations of acid and salt are not very dilute, the K a is fairly small
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Tro, Chemistry: A Molecular Approach 7 Henderson–Hasselbalch Equation What is the pH of a buffer that is 0.12 M in lactic acid, HC 3 H 5 O 3 , and 0.10 M in sodium lactate? K a for lactic acid is 1.4 × 10 −4 .
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Tro, Chemistry: A Molecular Approach 8 pH = p K + log [base] [acid] pH = −log (1.4 × 10 ) + log (0.10) (0.12) pH = 3.85 + (−0.08) pH = 3.77 What is the pH of a buffer that is 0.12 M in lactic acid, HC 3 H 5 O 3 , and 0.10 M in sodium lactate? Ka for lactic acid is 1.4 × 10− 4 . Henderson–Hasselbalch Equation
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Tro, Chemistry: A Molecular Approach 9 Common Ion Effect HA ( aq ) + H 2 O ( l ) A ( aq ) + H 3 O + ( aq ) What happen if CH 3 COONa is added? (that is the conjugate base of the acid)- suppress H 3 O + -less acidic (causes the pH to be higher than the pH of the acid solution)- causes the equilibrium to shift to the left
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Tro, Chemistry: A Molecular Approach 10 If acetate ion is added to the solution of acetic acid, Le Châtelier says the equilibrium will shift to the left. ionization of a weak electrolyte is decreased by adding a strong electrolyte that has an ion in common with the weak electrolyte .”- common ion effect AABTGZYO
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Tro, Chemistry: A Molecular Approach 11 Practice: The Common-Ion Effect Calculate the fluoride ion concentration and pH of a solution that is 0.20
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Chapter16_LEC - Chapter 16 Aqueous Ionic Equilibrium...

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