®
D r o p C o u n t e r
PS-2117
2
a titration. Data from the Drop Counter and other sensors are
recorded and displayed in software such as PASCO Capstone, or
on a datalogging interface such as an Xplorer GLX.
The Drop Counter can be mounted on a support rod and the sup-
port rod can be clamped to a rod stand. The counter is equipped
with three integrated probe holders. The included Micro Stir Bar
fits onto the end of a pH probe or probe of the same diameter.
Acid-base Titration
These steps explain a typical use of the Drop Counter.
Procedure
1.
Set up the equipment and consumables as illustrated in Fig-
ure 1. Attach both stopcocks to the syringe, and attach the
drop tip to the bottom stopcock. Line up the drop tip with the
rectangular opening in the Drop Counter.
2.
Start with the valves of the stopcocks turned parallel to the
table top. Add the solutions to the syringe and beaker.
3.
Write down the initial volumes of both solutions (in the
syringe and in the beaker), and the molarity of the titrant (in
the syringe).
4.
Connect the Drop Counter and pH sensor to your PASPORT
compatible PASCO interface (or interfaces).
5.
If you are using a computer, connect the interface to it and
start the data acquisition software.
6.
Start the stir plate.
7.
Click or press the start button to begin recording data.
8.
Open the top stopcock. Slowly adjust the bottom stopcock to
start delivering titrant at about 2 drops per second.
9.
Observe the data appearing on the pH versus drop count
graph (Figure 2). After the equivalence point is reached, wait
until the pH curve flattens.
Figure 2: Graph of pH versus drop count
10.
Close the stopcocks.
11.
Stop data recording.
12.
Read the final volume of fluid in the syringe and calculate
the net volume of titrant that was dispensed.
13.
Read the final drop count on the graph.
14.
In the calculator window of the software or datalogger, enter
a calculation as shown below, but using your own values of
total volume dispensed and final drop count. The calculation
gives the volume of titrant dispensed over time based on the
number of drops and the average volume per drop.
volume = [Drop Count (drops)] * 100/3050
In this example, “100” is the total volume dispensed (in mL)
and “3050” is the final drop count.
15.
In the graph, change the horizontal axis to the calculated
“volume” (Figure 3).
150 mL
beaker with
100 mL of
0.005 M HCl
Stir Plate
pH
Probe
Drop
Counter
Figure 1: Titration set-up
Micro
Stir Bar
60 mL syringe
with 50 mL of
0.1 M NaOH
Stopcock
Stopcock
Drop
Counter
Drop Tip
Three-finger
Clamp
Multi Clamp
equivalence point
final drop count
