Chpt 15 Lec - Chemistry 8/e Steven S. Zumdahl and Susan A....

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Chapter 15 Chemistry 8/e Steven S. Zumdahl and Susan A. Zumdahl Applications of aqueous equilibria 1
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• Acid-Base Equilibria – Common Ion Effect – Buffers – Titration Curve – Indicators • Solubility – Solubility Product – Common Ion Effect – pH and Solubility • Complex Equilibria – Complexes and Solubilities Applications of Aqueous Equilibria 2
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Common Ion in Acid-Base • Le Châtelier’s Principle: restoration of equilibrium consumes addends . • Addition of an ion already in equilibrium (Common Ion Effect) restores K by consuming the common ion. NH 3 + H 2 O → NH 4 + + OH Add HO - 3
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The common ion effect is the shift in equilibrium caused by the addition of a compound having an ion in common with the dissolved substance. The presence of a common ion suppresses the ionization of a weak acid or a weak base. Consider mixture of CH 3 COONa (strong electrolyte) and CH 3 COOH (weak acid). CH 3 COONa ( s ) Na + ( aq ) + CH 3 COO - ( aq ) CH 3 COOH ( aq ) H + ( aq ) + CH 3 COO - ( aq ) common ion 4
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What is the pH of a solution of 0.10 M CH 3 COOH and 0.20 M CH 3 COONa? 5
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Buffers A solution that is resistant to change in pH upon addition of small amounts of acid or base Mixture of weak acid - HX and its conjugate base - X - Buffer has: acidic species to neutralize base basic species to neutralize acid OH - + HX X - + H 2 O [X - ] [HX] constant => pH doesn’t change Examples: CH 3 COOH + CH 3 COO - H 2 PO 4 - + HPO 4 -2 acid conj. base 6
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Which of the following are buffer systems? (a) KF/HF (b) KCl/HCl, (c) Na 2 CO 3 /NaHCO 3 7
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What is the pH of a solution containing 0.30 M HCOOH and 0.52 M HCOOK?
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Calculate the pH of the 0.30 M NH 3 /0.36 M NH 4 Cl buffer system. 9
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Buffers 1) Mixture of weak acid HX and its conjugate base X - 2) Mixture of weak base B and its conjugate acid BH + What happens when a strong base or strong acid is added to a buffer? pH changes. Calculate pH of a buffered solution: 10 Kw = Ka x Kb or pka + pKb = 14
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What is the pH after the addition of 20.0 mL of 0.050 M NaOH to 80.0 mL of the buffer solution?
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How a Buffer Withstands Large Changes in pH (CH 3 COO)H/Na(CH 3 COO - ) 12
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Consider an equal molar mixture of CH 3 COOH and CH 3 COONa Add strong acid H + ( aq ) + CH 3 COO - ( aq ) CH 3 COOH ( aq ) Add strong base OH - ( aq ) + CH 3 COOH ( aq ) CH 3 COO - ( aq ) + H 2 O ( l ) How a Buffer Withstands Large Changes in pH (CH 3 COO)H/Na(CH 3 COO - ) Base of buffer removes excess H + Acid of buffer removes excess OH - 13
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A buffer solution is the most effective if . .. 1) there are large amounts of acid/conjugate base
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Chpt 15 Lec - Chemistry 8/e Steven S. Zumdahl and Susan A....

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