6611 2222 Chapter 19 Ionic Equilibria in Aqueous Systems NOTE the steeply

6611 2222 chapter 19 ionic equilibria in aqueous

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6/6/11 2222 Chapter 19 Ionic Equilibria in Aqueous Systems NOTE: the steeply rising curve at the equivalence point NOTE: the pH at the equivalence point of a strong acid-strong base titration is at 7.00. Only neutral substances are present at this point.
6/6/11 2323 Chapter 19 Ionic Equilibria in Aqueous Systems 2. Weak Acid-Strong Base Titrations HA(aq) + OH (aq) H 2 O( l ) + A (aq) Weak acid Weak conjugate base Equilibrium calculations will be required to find the pH of a solution of a weak acid and/or weak base. Example Problem : Calculate the pH at each point during the titration of 40.0 mL of 0.100 M HC 3 H 5 O 2 with 0.100 M NaOH. a. 0.00 mL of NaOH added - What is in the flask? -calculate the pH:
6/6/11 2424 Chapter 19 Ionic Equilibria in Aqueous Systems b. 10.0 mL of NaOH added: - What is in the flask? Do the stoichiometry: - Calculate the pH:
6/6/11 2525 Chapter 19 Ionic Equilibria in Aqueous Systems c. 20.0 mL of NaOH added: - What is in the flask? Do the stoichiometry HC 3 H 5 O 2 (aq) + OH (aq) H 2 O( l ) + C 3 H 5 O 2 (aq) - Calculate the pH
6/6/11 2626 Chapter 19 Ionic Equilibria in Aqueous Systems d. 40.0 mL of NaOH added: - What is in the flask? Do the stoichiometry HC 3 H 5 O 2 (aq) + OH (aq) H 2 O( l ) + C 3 H 5 O 2 (aq) - Calculate the pH
6/6/11 2727 Chapter 19: Ionic Equilibria in Aqueous Systems
6/6/11 2828 Chapter 19 Ionic Equilibria in Aqueous Systems HA(aq) + OH (aq) H 2 O( l ) + A (aq) Weak acid Weak conjugate base NOTE: pH changes more slowly near the equivalence point. NOTE: the pH at the equivalence point of a weak acid-strong base titration is > 7
6/6/11 2929 Chapter 19 Ionic Equilibria in Aqueous Systems 3. Strong Acid-Weak Base Titration B(aq) + H + (aq) BH + (aq) Weak base Conjugate weak acid Equilibrium calculations will be required to find the pH of a solution of a weak acid and/or weak base. NH 3 (aq) + H + (aq) NH 4 + (aq) 1. NOTE: The pH at the equivalence point of a strong acid-weak base titration is < 7.
6/6/11 3030 Chapter 19 Ionic Equilibria in Aqueous Systems
6/6/11 3131 Chapter 19 Ionic Equilibria in Aqueous Systems Characteristics of Acid-Base Titrations (Spectator ions marked in bold ) Strong acid-strong base titration Weak acid-strong base titration Strong acid-weak base titration Example H NO 3 + K OH H 2 O + K + + NO 3 HF + K OH H 2 O + K + + F H NO 3 + NH 3 NH 4 + + NO 3 pH at equivalence point 7.0 > 7.0 < 7.0 Species present at the equivalence point H 2 O and spectator ions H 2 O, conjugate weak base and spectator cation Conjugate weak acid and spectator anion
6/6/11 3232 Chapter 19 Ionic Equilibria in Aqueous Systems Acid-Base Indicators Acid-Base Indicators: HIn(aq) H + (aq) + In (aq) Acid form (one color) Base form (different color) Indicator pK a pH range of color change Acid Color Base color methyl orange 3.4 3.2 - 4.4 red yellow bromophenol blue 3.9 3.0 - 4.6 yellow blue bromocresol green 4.7 3.8 - 5.4 yellow blue methy red 5.0 4.8 - 6.0 red yellow thymol blue 8.9 8.0 - 9.6 yellow blue phenolphthalein 9.4 8.2 - 10.0 colorless pink alizarin 11.7 11.0 - 12.4 red purple
6/6/11 3333 Chapter 19 Ionic Equilibria in Aqueous Systems
6/6/11 3434 Chapter 19 Ionic Equilibria in Aqueous Systems HIn(aq) H + (aq) + In (aq) When [HIn] 10 : [In ] - When [HIn] 0.1 : [In ] - When [HIn] 1 : [In ] -
6/6/11 3535 Chapter 19 Ionic Equilibria in Aqueous Systems Each indicator has a particular value of K a that affects at what pH values a color change occurs.

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• Spring '08
• AMATEIS
• Chemistry, pH, Ionic equilibria, Aqueous Systems