Buffers

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Slide 1

Buffers and Acid/Base Titration

Slide 2

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

Slide 3

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?

Slide 4

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!)

Slide 5

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

Slide 6

Acid/Salt Buffering Pairs

The salt will contain the anion of the acid, and the cation of a strong base (NaOH, KOH)

Slide 7

Base/Salt Buffering Pairs

The salt will contain the cation of the base, and the anion of a strong acid (HCl, HNO3)

Slide 8

Titration of an Unbuffered Solution

A solution that is

0.10 M CH3COOH

is titrated with

0.10 M NaOH

Slide 9

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

Slide 10

Comparing Results

Buffered

Unbuffered

Slide 11

Comparing Results

Unbuffered

Buffered

In what ways are the graphs different?

In what ways are the graphs similar?

Slide 12

Henderson-Hasselbalch Equation

This is an exceptionally powerful tool, and it’s use will be emphasized in our problem solving.

Slide 13

Weak Acid/Strong Base Titration