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Diffusion Coefficient Apparatus Essay

General Start-up Procedure:
 Prior to running an experiment, students are advised to perform the following startup procedure.
 Fill the water with clean (preferably filtered) water to approximately 20 mm from the top.
 Plug the main cable to the electrical supply. Be sure that the voltage of the supply is correct to suite the equipment.
 Switch on the main power on the control panel.
 Adjust the set-point value on the temperature controller to 500C.

Warning!!

Do not set the temperature controller beyond 700C.

Switch on the heater. Observe the water temperature heats up to 50 0C and remain constant.
The equipment is now ready for experiment.

Priming procedure for capillary Tube:
Before using the capillary tube in an experiment using acetone, students are advised to clean the inside of the tube.
 Prepare a weak solution of detergent.
 Use the Hirschman pipette to fill the tube with the solution. Tapping the of side of the tube may be necessary if the solution is trapped and does not flow down.
 Turn the tube upside-down and shake. Empty the tube.

 Repeat steps 2 to 3 with acetone.
 The tube is now ready for student experiment.

General Shut-down Procedure:
 After the completion of an experiment, students are advised to shut down the equipment as follows:

 Switch off the heater and air pump.
 Adjust the set-point value of the temperature controller to approximately 5 degree below the room temperature.

 Allow the water to cool down until it is safe to touch. Open the drain valve and empty the water tank.

 Detach the flexible tubing and clean the capillary tube for next use. (Refer to priming procedure)

 Switch off the main power. Unplug the main cable if the equipment will not be used for a long period.

EXPERIMENT
OBJECTIVE:
To determine gas diffusion coefficient of acetone using the established Winkelmann’s method.

Procedure:
1. Perform the start-up procedure.
2. Partially fill the capillary tube with acetone to a depth of about 35 mm.
3. Carefully insert the capillary tube through the fitting on the top of the water bath cover. Do not over-tighten the fitting.
4. Observe the initial level of acetone through the telescope. Record the level of acetone.
5. Connect the flexible tubing from the air pump line to one end of the capillary tube. Switch on the air pump.
6. After 30 minutes, switch off the air pump. Disconnect the flexible tubing and close the two capillary tubes ends with the cap provided. Observe and record the level of acetone.
7. Repeat steps 4 to 6 at 30 minutes intervals.

ANALYSIS & DISCUSSION:
Plot t/ (L-L0) against (L-L0).Determine gas diffusivity, D from the obtained slope, S. Compare the experimental value with the theoretical value that can be predicted from empirical equations (e.g. modified Maxwell’s equation by Gilliland).


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