PASCO PASPort PS-2117 Instruction Sheet

®

Drop Counter

Micro Stir

Bar

Syringe

Support Rod

Stopcock (2)

Drop Tip

PS-2117 Drop Counter

PS-2117

Instruction Sheet

012-08470D

Included Parts

• Drop Counter • Stopcock (2)

• Micro Stir Bar • Drop Tip

• Syringe (60 mL) • Support Rod

Additional Parts Required

• PASPORT compatible PASCO interface or datalogger

• Three-finger Clamp (SE-9445)

• Support Rod and Stand (SE-9451)

• Multi Clamp (ME-9507)

• Magnetic Stir Plate (SE-77 00)

• Beaker , 150 mL

Additional Parts Recommended

• Buret, 50 mL (SE-7703)

• Chemistry Sensor (PS-2170)

• pH Sensor (PS-2102)

• Temperature Sensor (PS-2125)

• Other sensors for measuring conductivity or
oxygen-reduction potential (ORP)

• Micro Stir Bars, set of 5 (PS-2565)

Quick Start

1. Connect the Drop Counter to your PASPORT compatible
PASCO interface.

2. If you are using a computer, connect the interface to it and
start the data acquisition software.

3. Press or click the start button to begin recording data.

4. Allow drops of liquid to fall through the rectangular open-

ing.

Introduction

The Drop Counter measures the number of drops of fluid that fall
through the rectangular opening of the sensor. It is typically used
in conjunction with a pH sensor and other equipment to perform

®

Drop Counter PS-2117

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

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 sup­port 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).

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®

Drop Counter PS-2117

Select volume calculation

for horizontal axis

detector

collimating

lens

focusing
lens

sheet of light

dropinfrared light

source

Figure 4: Diagram of Drop Counter

When the Drop Counter detects a falling drop, the green indicator
light emitting diode (LED) flashes. If something stationary is
blocking the photodetector, the indicator LED remains on.

Troubleshooting

Problem Cause Solution

Figure 3: Graph of pH versus volume

Tips

• Except for opening and closing the stopcocks, do not touch
the syringe during the titration; otherwise, the drop size may
change significantly .

• The drop rate must remain approximately constant (about 2
drops per second) in order for the drop size to remain con­stant.

• Drop size depends on the exact position of the bottom stop­cock. Therefore, the average drop size will be different for
every titration. For each titration, re-enter the volume used
and drop count values in the calculation.

Other Titrations

Titrations with different solutions can be performed using the
same equipment and procedure. Other probes (such as conductiv­ity or ORP) can be used in place of the pH probe.

Indicator light flashes
twice for a single drop.
Drop Counter registers
more drops than
actually dispensed.

Indicator LED remains
on constantly. Drop
Counter does not
register drops.

Fluid is splashing
back into the drop
window.

Lenses in drop
window are dirty or
wet.

Adjust the position
of the beaker, Drop
Counter, or syringe
to eliminate splash
back

Clean lenses with
water and dry with a
cotton swab or
tissue.

Specifications

Maximum drop rate 40 drops per second
Default sample rate 5 samples per second
Maximum sample rate 10 samples per second
Minimum object detection size 0.64 mm diameter
Enclosure Polypropylene, water resistant,

Detector type Infrared photodetector with

chemically resistant to mild acids
and bases

collimating lens

Technical Support

For assistance with any PASCO product, contact PASCO at:

Theory of Operation

The Drop Counter uses an
infrared light source and a
photodetector. Lenses
spread the light into a
“sheet” and refocus it
onto the photodetector.
When a drop of fluid
passes through the Drop
Counter, it partially
blocks this sheet of light, and the photodetector registers a
momentary decrease in light intensity.

The Drop Counter uses infrared light and ignores visible light.
On power up, it automatically adjusts the light level for the best
sensitivity. Use the Drop Counter away from direct sunlight or
other sources of infrared that may interfere with it.

Address: PASCO scientific

10101 Foothills Blvd.
Roseville, CA 95747-7100

Phone: [phone] (worldwide)

800-772-8700 (U.S.)
Web: www.pasco.com
Email: [e-mail]

For more information about the Drop Counter and the latest revi­sion of this Instruction Sheet, visit the PASCO web site and enter
PS-2117 in the Search window.

Limited Warranty For a description of the product warranty, see the
PASCO catalog. Copyright The PASCO scientific 012-08470D Drop
Counter Instruction Sheet is copyrighted with all rights reserved. Permis­sion is granted to non-profit educational institutions for reproduction of any
part of this manual, providing the reproductions are used only in their labo­ratories and classrooms, and are not sold for profit. Reproduction under

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®

Drop Counter PS-2117

any other circumstances, without the written consent of PASCO scientific,
is prohibited. Trademarks PASCO, PASCO scientific, PASCO Cap­stone, PASPORT, and Xplorer GLX are trademarks or registered trade­marks of PASCO scientific, in the United States and/or in other countries.
All other brands, products, or service names are or may be trademarks or
service marks of, and are used to identify, products or services of, their
respective owners. For more information visit www.pasco.com/legal.

Product End of Life Disposal Instructions:

This electronic product is subject to disposal and recycling regu­lations that vary by country and region. It is your responsibility to
recycle your electronic equipment per your local environmental
laws and regulations to ensure that it will be recycled in a manner
that protects human health and the environment. To find out
where you can drop off your waste equipment for recycling,
please contact your local waste recycle/disposal service, or the
place where you purchased the product.

The European Union WEEE (Waste Electronic
and Electrical Equipment) symbol (to the right)
and on the product or its packaging indicates
that this product must not be disposed of in a
standard waste container.

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