A
buffer solution is a solution that changes
pH only slightly when small amounts of a
strong acid or a strong base are added.
 A buffer contains significant concentrations
of both
a
weak acid and its conjugate
base, or
 a weak base and its conjugate
acid.
 This
buffer relies on the dissociation reaction
of acetic acid.
CH3COOH
Buffer animation
CH3COO- + H+
 Our
blood is buffered to a pH of 7.4
 Buffers are used when pH must be controlled
in experiments.


Proteins
Enzymes
Pure water increases in pH by
about 5 pH units when the OH– is
added, and decreases by about 5
pH units when the H3O+ is added.
In contrast, the same amounts of
OH– and H3O+ added to a buffer
solution barely change the pH.
There is a limit to the ability of a buffer solution to
neutralize added acid or base.
 This buffer capacity is reached before either buffer
component has been consumed.
 As a rule, a buffer is most effective if the
concentrations of the buffer acid and its conjugate
base are equal or nearly so.

 Determine
the buffer capacity of 3 different
concentrations of sodium acetate buffer
using an acid and a base.
 We
will be using HCl and NaOH so you must
wear lab coat, goggles, and gloves at all
times!
1.
2.
3.
4.
Label one 250 mL beaker acid and the
other one base.
Pour 50 mL of 1.0 M acetic acid buffer into
each of the beakers.
In the beaker labeled base, add 1 mL of
Universal Indicator. In the beaker labeled
acid, add 1 mL methyl orange.
Measure and record the pH of each
solution.
5.
6.
7.
8.
Using a disposable pipet, add 1 mL of
1.0 M HCl to the beaker labeled acid.
Mix well. Measure and record the pH.
Continue adding HCl 1 mL at a time
until the pH and the color of solution
changes.
Repeat steps 5-6 using the NaOH and
the base beaker.
Rinse both beakers out and repeat steps
3-7 using the 0.1 M buffer and then the
0.01 buffer.
 Make
a Data Table to record your pH values.
Buffer
mL of HCl
Concentration
1.0 M
0.1 M
0.01
pH
mL of NaOH
pH
 Graph
your data with pH on the y-axis and
volume of acid/base on the x-axis.
 Don’t forget to include the units and titles
for each axis. Your graph should also have a
main title and a legend.
1.
2.
3.
4.
How does the concentration of the buffer
affect the buffer capacity?
How is the HCl graph different from the NaOH
graph?
Write reaction equations to explain how your
acetic acid-acetate buffer reacts with an acid
and reacts with a base.
What is the buffer capacity of each buffer
used (for both HCl and NaOH)?