The purpose of this activity is to introduce the concept of a buffer. Students will learn that a buffer is a system
that resists a change in pH.
In doing this activity, students will learn to collect data
as selected events, use the store run
option under file, and learn that they can display two plots simultaneously (L2 and L3 versus L1) using EasyData. Materials:
- CBL2 system
- pH probe
- 2 beakers (100 mL)
- magnetic stirrer
- wash bottle
- tonic water
- 1 M NaHCO3 solution
- 1 M HCl in a labeled pipet
In this experiment, the pH
will be monitored as five drops of 1M HCl are added drop by drop to a beaker of water. EasyData will be used to collect the data
in the selected events format. After storing this run, the same procedure will repeated using 50 mL of a buffered solution
(25 mL of tonic water and 25 mL of 1M NaHCO3). The plots will be compared to illustrate how a buffered solution
resists a change in pH.
As an extension, students could be asked to repeat the process, substituting 1 M NaOH for the 1 M HCl.
Note: This activity serves to introduce the topic of buffers by allowing students to graphically visualize how resistant buffers are to changes in pH. Students actually create a two component buffer consisting of H2CO3 and NaHCO3
. With this knowledge, the teacher can build the concept of buffer consisting of a weak acid
and weak base
containing a common ion. This buffer system
is of particular relevance since it is responsible for maintaining pH
stability in the blood.