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Buffers and Acid/Base Titration. Reaction of Weak Bases with Water. The base reacts with water, producing its conjugate acid and hydroxide ion:. CH 3 NH 2 + H 2 O CH 3 NH 3 + + OH - K b = 4.38 x 10 -4. K b for Some Common Weak Bases.

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## Buffers and Acid/Base Titration

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**Reaction of Weak Bases with Water**The base reacts with water, producing its conjugate acid and hydroxide ion: CH3NH2 + H2O CH3NH3+ + OH- Kb = 4.38 x 10-4**Kb for Some Common Weak Bases**Many students struggle with identifying weak bases and their conjugate acids.What patterns do you see that may help you?**Reaction of Weak Bases with Water**The generic reaction for a base reacting with water, producing its conjugate acid and hydroxide ion: B + H2O BH+ + OH- (Yes, all weak bases do this – DO NOT endeavor to make this complicated!)**Buffered Solutions**A solution that resists a change in pH when either hydroxide ions or protons are added. Buffered solutions contain either: A weak acid and its salt A weak base and its salt**Acid/Salt Buffering Pairs**The salt will contain the anion of the acid, and the cation of a strong base (NaOH, KOH)**Base/Salt Buffering Pairs**The salt will contain the cation of the base, and the anion of a strong acid (HCl, HNO3)**Titration of an Unbuffered Solution**A solution that is 0.10 M CH3COOH is titrated with 0.10 M NaOH**Titration of a Buffered Solution**A solution that is 0.10 M CH3COOH and 0.10 M NaCH3COO is titrated with 0.10 M NaOH**Comparing Results**Buffered Unbuffered**Comparing Results**Unbuffered Buffered • In what ways are the graphs different? • In what ways are the graphs similar?**Henderson-Hasselbalch Equation**This is an exceptionally powerful tool, and it’s use will be emphasized in our problem solving.**Weak Acid/Strong Base Titration**A solution that is 0.10 M CH3COOH is titrated with 0.10 M NaOH Endpoint is above pH 7**Strong Acid/Strong Base Titration**Endpoint is at pH 7 A solution that is 0.10 M HCl is titrated with 0.10 M NaOH**Strong Acid/Strong Base Titration**A solution that is 0.10 M NaOH is titrated with 0.10 M HCl Endpoint is at pH 7 It is important to recognize that titration curves are not always increasing from left to right.**Strong Acid/Weak Base Titration**A solution that is 0.10 M HCl is titrated with 0.10 M NH3 Endpoint is below pH 7**Indicator Transitions**Source: Wikipedia

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