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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

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