PASCO ME-6940 User Manual
®
Instruction Manual
Sensor
Mounting Stud
Semi-permeable
Membranes (25)
Diffusion-Osmosis
Apparatus
Tubing
Quick-release
Connectors
Caps
Bolts
Bolt
Bolt
Alignment
Tab s
Figure 1
012-10962A
*012-10962*
Diffusion-Osmosis Apparatus
ME-6940
Introduction
semi-permeable membrane. With the use of other sensors like conductivity, pH, carbon dioxide gas or oxygen
gas, students can explore the diffusion of molecules
Open any biology textbook to the osmosis section and
across the semipermeable membrane.
you will find the image of a U-shaped tube composed of
two clear columns separated by a semi-permeable membrane. (See Figure 1.) This classic figure is the most
commonly used model to visualize the osmotic movement of water due to a concentration gradient. PASCO's
ME-6940 Diffusion-Osmosis Apparatus is a U-shaped
apparatus consisting of two cylinders separated by a
semi-permeable membrane. The transparent, graduated
cylinders allow students to observe and measure volume
changes due to osmosis. In conjunction with the
PASPORT Dual Pressure Sensor, the apparatus allows
students to measure the changes in pressure and volume
caused by the osmotic movement of water across a
800-772-8700 www.pasco.com
Model No. ME-6940 About the Membrane
The ME-6940 Diffusion-Osmosis Apparatus is patent pending.
Sensor Model
PASPORT Dual Pressure Sensor PS-2181
Optional Sensors Model
PASPORT Carbon Dioxide Gas Sensor PS-2110
Carbon Dioxide Gas Sensor CI-6561
PASPORT Oxygen Gas Sensor PS-2126
Oxygen Gas Sensor CI-6562
Other Model
Replacement Membranes (20) ME-6941
Diffusion-Osmosis Kit* ME-6942
*The ME-6942 Diffusion-Osmosis Kit includes the Diffusion-Osmosis Apparatus and the PASPORT Dual Pressure
Sensor.
The PASPORT sensors work with a PASPORT interface such as the ones listed below. The CI-6561 Carbon Dioxide
Oxygen Gas Sensor and CI-6562 Oxygen Gas Sensor work with a ScienceWorkshop interface or can work with a
PASPORT interface when connected to a PS-2158 Analog Adapter..
PASPORT Interface Model ScienceWorkshop Interface Model
Xplorer GLX PS-2002 ScienceWorkshop 750 CI-7650
Xplorer PS-2000 ScienceWorkshop 500 CI-6400
PowerLink PS-2001
USB Link PS-2100 Other Model
SPARK Science Learning System PS-2008 PASPORT Analog Adapter PS-2158
SPARKlink PS-2009
See the PASCO catalog or the PASCO web site at www.pasco.com for more information about PASCO sensors and
interfaces.
About the Membrane
• The Diffusion/Osmosis membrane is a regenerated cellulose membrane preserved in glycerol.
• In order to conserve moisture, membranes should be stored in an airtight, moisture-proof container in a cool
location. If the membranes are not stored correctly, they can dry out, lose flexibility and develop microscopic
holes that will alter expected experimental results.
• Tension on the membrane in one direction can reduce pore size slightly. Tension on the membrane in both
directions can increase pore size slightly.
• Membranes can be reused if the wetted membranes are stored in either acid or formaldehyde. Be sure to soak
and rinse again.
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Model No. ME-6940 Using the Apparatus
• Membranes cannot be reused if they are allowed to dry out. Drying causes unrecoverable collapse of the pore
structure.
• Membranes are resistant to the following groups: halogenated hydrocarbons, alcohols, ketones, esters, oxides
and solvents containing nitrogen.
• Membranes are not resistant to the following: greater than 25% hydrochloric, nitric or perchloric acids; 96%
sulfuric acid; 1 N potassium hydroxide; and 10% phenol.
Specifications
Pore size 40-50 m (micrometers)
Molecular weight cut-off 6,000 daltons
Temperature range 4 °C - 60 °C
pH range 2 - 12
Maintenance and Care
• Always disassemble the apparatus after an experiment. Empty all fluid from the cylinders and separate the
two cylinders to remove the membrane. Rinse the inside and outside of the cylinders, including the O-rings
and the area around the O-rings, with cool, warm or hot water. Soap may be used, but is not necessary. Dry the
rinsed pieces of the apparatus on a paper towel or drying rack.
• Reassembling the apparatus before long-term storage will help to ensure that all of the pieces stay together.
• The columns are dishwasher-safe but be sure to remove the O-rings first! Do not put the blue caps and plastic
tubing in the dishwasher.
Safety
• Be careful when removing the caps from the columns as pressure may have built up during your experiment.
• Protect your eyes by wearing protective eyewear. Do not lean over the apparatus if pressure has accumulated,
or when removing the caps.
• Pressure in the columns can be as great as 15 pounds per square inch (psi).
Using the Apparatus
1. Soak the membranes: Before using the membrane, soak it in distilled water for at least 30 minutes (at room
temperature) to remove the preservative on the membrane. Then rinse the membrane thoroughly with distilled
water.
2. Prepare your solutions: Prepare the solutions necessary for your experiment. If the solutions have been prepared beforehand and stored in refrigerator, be sure to bring the solutions to room temperature before starting the
experiment.
3. Assemble the apparatus:
• Start with a clean, dry apparatus and a soaked, rinsed membrane. Unscrew the four bolts and place them in a
safe location. Separate the two cylinders.
• Line up two of the four corner holes on the soaked membrane with the two raised pegs on one of the cylinders.
It does not matter which cylinder you put the membrane on.
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Model No. ME-6940 Using the Apparatus
Membrane
Cylinder
Peg
Peg
Figure 2
Figure 3
Dual Pressure
Sensor
• Ensure that the two holes of the membrane are lined up with the pegs on the cylinder and then carefully place
the other cylinder against the membrane so that the two raised pegs on the second cylinder go into the two
empty holes on the membrane. Ensure that the membrane is securely in place between the two O-rings, all
four raised pegs are inserted into the membranes holes and the membrane is pulled tightly across the space,
with no folds or gaps. Make sure that the two alignment tabs near the top of the cylinders are aligned.
• Quickly and carefully, screw in the four bolts and ensure that they are tight. The two cylinders should be
tightly secured to each other with the membrane separating the space between the two cylinders.
*You may wish to label the two cylinders (1 & 2) with a sticker or marker. This will help reduce confusion if
the solutions are similar in color.
4. Fill the cylinders: Immediately after placing the membrane in the apparatus, fill the cylinders with your solutions. Do not allow the membrane to dry out! Pour the required amount of solution into the first cylinder. Tilt the
apparatus in all directions (careful not to spill the solution) to allow any bubbles in the bottom of the cylinder to
escape. Repeat with the second cylinder. If you expect the volume within the cylinder to increase during your
experiment, do no fill the cylinder with greater than 60 mL of solution, as the solution will overflow, or enter the
plastic tubing and harm the sensor.
If you are using a Dual Pressure Sensor (or other PASPORT pressure sensor) in your experiment, place the
blue cap into the first cylinder, press it down and then turn the cap to seal the cylinder. Repeat with the second
cylinder.
5. Set up your interface: Connect the sensor to the interface. View
Absolute Pressure 1, Absolute Pressure 2 and 1-2 Differential pressure in a digits display. Also view 1-2 Differential Pressure in a
graph display.
6. Reduce the sampling rate: Because diffusion and osmosis experiments take time, reducing the sampling rate of the sensor is necessary so that the interface is not overloaded with massive amounts of
data. The default sampling rate of the PASPORT Dual Pressure
Sensor is 10 Hz (or 10 samples per second). Reduce the sampling
rate to 1 or 2 samples per minute.
7. Connect the apparatus to the sensor: Attach the quick-release
connectors at the ends of the two plastic tubes to the Dual Pressure
Sensor. (See Figure 3.) After you connect the apparatus to the pressure sensor, allow the system to equilibrate for five minutes before
beginning data collection.
8. Calibrate the sensor: If you are using the PASPORT Dual Pressure Sensor, calibrate Absolute Pressure 1 and Absolute Pressure 2
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