Name ________________________________________________________ Th 2/20 and F 2/21
Buffer Lab
=
/ 100 points
/ 50 in gradebook
Your group will design a buffer using a weak acid or a weak
base (Thursday) and test its buffering capacity with HCl and NaOH (Friday).
Characteristic
Value
Explain how you created your buffer in the
space below.
HA
A[HA]
Write the two equations that describe your
buffer’s interaction with added H+ and OH-.
[A-]
Ka
pH of buffer
Each group will test 100 mL of their buffer with .100 M and HCl and NaOH (200 mL of buffer are
needed altogether). 100 mL of water will be tested in the same way with HCl and NaOH for
comparison.
Fill out the table below with the pH for each addition of acid/base to 100 mL of your buffer and 100
mL of water.
Buffer, 0.1 M HCl Water, 0.1 M HCl
Buffer, 0.1 M NaOH
Water, 0.1 M NaOH
0 mL added
25 mL added
50 mL added
100 mL added
125 mL added
150 mL added
Graph the data for your buffer and for water on the graphs provided on the last page of this lab.
Analysis
1) Qualitative
a. Did your buffer resist changes to its pH more effectively than water? Give evidence
for your answer.
2) Quantitative
a. Buffering capacity can be calculated by dividing the number of moles of strong acid
or strong base added to a buffer, by the resulting change in pH. Calculate the
buffering capacity of your buffer at each point in the table below.
pH of Buffer,
0.1 M HCl
0 mL added
Buffering Capacity,
0.1 M HCl
----
pH of Buffer,
0.1 M NaOH
Buffering Capacity,
0.1 M NaOH
----
25 mL added
50 mL added
100 mL added
125 mL added
150 mL added
b. What happens to buffering capacity as more HCl or NaOH is added? Give a
thorough explanation for your observations.
c. Calculate the buffering capacity of water at the 50 mL mark for both HCl and NaOH.
Show your work below, and comment on the difference between the buffering
capacity of water and the buffering capacity of water at the 50 mL mark.
Group
d. Compare your 50 mL added buffering capacity for HCl and NaOH with the other
groups in class. Record the class’s data below.
Buffer Used (HA and
50 mL Buffering
50 mL Buffering
[HA], A and [A ])
Capacity, 0.1 M HCl
Capacity, 0.1 M NaOH
e. Which buffer had the highest buffering capacity, and why?
3) What characteristics make a strong buffer? Also explain how you would change your buffer
if you wanted to increase its buffering capacity.
4) What real-world applications could your specific buffer solution serve?
This lab is half of a major grade. It is due on F 2/28 and will not be accepted late.
Buffering Capacity with HCl
14
13
12
11
10
9
8
pH
7
6
5
4
3
2
1
0
25
50
75
100
125
150
125
150
Volume of HCl Added (mL)
Buffering Capacity with NaOH
14
13
12
11
10
9
8
pH
7
6
5
4
3
2
1
0
25
50
75
100
Volume of NaOH Added (mL)