Gas Diffusion Essay

Aim:
Determine the gas diffusion coefficient of propanone utilizing the established Winkelmann’s method

KEYWORDS
Diffusivity. Gas Diffusion Coefficient. Winkelmann’s method

Overview

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The cognition of physical and chemical belongingss of certain stuffs is of import because really frequently process technology trade with the transmutation and distribution of these stuffs in majority. One such belongings is diffusivity. Mass transportation by diffusion takes topographic point when there is a concentration gradient of the diffusing constituent. Naturally. the diffusion in gas stage is much faster than the diffusion in liquid stage due to the little infinites between the molecules that hinder other molecule motion. Other factors that will consequence the diffusion are temperature. denseness. concentration and other external factors.

1. Introduction

This experiment has been designed for pupils experiment on the technique of finding diffusivity of the vapour of a volatile liquid based on the established Winkelmann’s method. In this method the volatile liquid is allowed to vaporize in a perpendicular glass tubing over the top of which a watercourse of vapor-free gas is passed. A H2O bath is provided for keeping a steady temperature so that there is no eddy current in the perpendicular tubing and mass transportation takes topographic point from the surface by molecular diffusion entirely. The rate of vaporization can be followed by the rate of autumn of the liquid surface. A going microscope is provided for finding. the liquid autumn. With the cognition of the concentration gradient. the diffusivity of the vapour of the volatile liquid can so be calculated.

2. Theory

When a concentration gradient exists within a unstable consisting of two or more constituents. there is a inclination for each component to flux in such a way as to cut down the concentration gradient. This is called mass transportation. Mass transportation takes topographic point in either a gas stage or a liquid stage or in both at the same time.

When a liquid is allowed to vaporize in a narrow perpendicular tubing and a steady temperature is maintained. mass transportation takes topographic point from the surface by molecular diffusion entirely. This is the technique developed by Winkelmann to find the diffusivity of the vapour of a volatile liquid. By supervising the vaporization rate. which is the rate of autumn of liquid surface. and with the cognition of concentration gradient. one may so cipher the diffusivity.

The rate of mass transportation is given by:

( 1 )
where.
D=diffusivity [ m2/s ]
CA=saturation concentration at interface [ kmol/m3 ]
L=effective distance of mass transportation [ m ]
CT=total molar concentration [ kmol/m3 ]
CBm=logarithmic average value of CB [ kmol/m3 ]





Sing the vaporization of the liquid:

( 2 )

where.
L=density of liquid [ kg/m3 ]
M=molecular weight [ kg/kmol ]

Uniting equations 1 and 2 we get.

( 3 )

Integrating and seting L = L0 at t = 0:

( 4 )

Valuess of L0 or L will non be measured accurately but accurate values of ( L – L0 ) are available.

Therefore. rearranging equation 4:

or. ( 5 )

A secret plan of t/ against will give a incline s:

( 6 )

Diffusivity D can so be calculated from equation 6:

3. Get down UP AND SHUT- DOWN PROCEDURES

3. 1Start-up Procedure

Prior to running an experiment. pupils are advised to execute the undermentioned start-up process:

1. Fill the H2O bath with clean ( sooner filtered ) H2O to about 30 millimeter from the top.

2. Plug the brinies overseas telegram to the electrical supply. Be certain that the electromotive force of the supply is right to accommodate the equipment.

3. Switch over on the chief power on the control panel.

4. Adjust the set-point value on the temperature accountant to 50 °C.

Warning! ! Do non put the temperature accountant beyond 70 °C.

5. Switch over on the warmer. Detect the H2O temperature heats up to 50 °C and remains changeless.

6. Switch over on the air pump. Adjust the needle valve so that a steady low speed of air watercourse is detected at the terminal of the flexible tube.

7. The equipment is now ready for student experiment.

B ) Priming Procedure for the Capillary Tube

Before utilizing the capillary tubing in an experiment utilizing propanone. pupils are advised to clean the interior of the tubing.

1. Fix a weak solution of detergent.

2. Use a Hirschmann pipette to make full the tubing with the solution. Taping the exterior of the tubing may be necessary if the solution is trapped and does non flux down.

3. Turn the tubing inverted and agitate. Empty the tubing.

4. Repeat steps 2 to 3 with propanone.

5. The tubing is now ready for student experiment.

degree Celsiuss ) Shut-down Procedure

After the completion of an experiment. pupils are advised to close down the equipment as follows:

1. Switch over off the warmer and air pump.

2. Adjust the set-point value of the temperature accountant to about 5 grade below the room temperature.

3. Let the H2O to chill down until it is safe to touch. Open the drain valve and empty the H2O armored combat vehicle.

4. Detach the flexible tube and clean the capillary tubing for following usage. ( Refer to priming process )

5. Switch over off the chief power. Unplug the chief overseas telegram if the equipment will non be used for a long period.

4. EXPERIMENTAL PROCEDURES

1. Perform the start-up process as outlined in subdivision 3.

2. Initially exchange off the air pump.

3. Partially fill the capillary tubing with propanone to a deepness of about 35 millimeters.

4. Carefully insert the capillary tubing through the adjustment on top of the H2O bath screen. Make non over-tighten the adjustment.

5. Detect the initial degree of propanone through the microscope. Record the degree in the tabular array.

6. Connects the flexible tube from the air pump line to one terminal of the capillary tubing. Switch over on the air pump.

7. After 10 proceedingss. exchange off the air pump. Unplug the flexible tube and detach the capillary tubing from the adjustment. Observe and enter the degree of the propanone.

8. Repeat steps 5 to 6 at 10 proceedingss intervals.

9. Record the clip. acetone degree and liquid autumn in the tabular array below.

5. 0RESULT

Time.
T
( Kansas )
Degree of
Acetone. L
( millimeter )
Liquid Fall
( L – L0 )
( millimeter )







t/ ( L – L0 )
( ks/mm )

6. 0TUTORIALS

6. 1 Plot t/ against. Determine gas diffusivity. D from the obtained incline. s. Attached all of your computation at the appendix in the experiment study. 6. 2 Compare the experimental value with the theoretical value that can be predicted from empirical equations ( e. g. modified Maxwell’s equation by Gilliland ) . 6. 3 Discuss the factors that consequence the diffusion of propanone from the graph that have been plotted. 6. 4 Base on aim of the experiment and the theory in gas diffusion makes a decision from your determination.

7. 0 SAFETY AND MAINTENANCE

General Safety Procedure

1. Always read and understand the manual properly before trying to run the equipment. 2. Always wear proper garb during research lab session. It is extremely recommended that oculus protection and baseball mitts are used. 3. Be careful when managing risky stuff. Always refer to the stuff safety informations sheet. Avoid inhaling in great sum any risky stuff. 4. Avoid any spillage onto electrical constituents to forestall electrical daze. 5. Avoid touching hot surfaces ( e. g. warmer ) to forestall skin burn. 6. Always conduct experiment in a decently ventilated room.

General Maintenance Procedure

1. Make non run the equipment if any of the constituents is found to be defective. Consult the teacher for aid. 2. Unplug the equipment from electrical supply when non in usage. 3. Drain the H2O from the H2O bath.

4. Clean the H2O bath exhaustively after usage.

Valuess for Calculation:

1. ? L = 760. 0 kg/m3
2. M = 58. 08 kg/kmol
3. Partial force per unit area P* = 0. 8062 standard pressure

4.

where for propanone.
CB1=0. 0377 kmol/m3
CB2=0. 00731 kmol/m3
CA=0. 0304 kmol/m3
CT=0. 0377kmol/m3



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