Vapour in Air Diffusion
Innovation Lab Experiment
Name
Roll Number
Abhishek Singh
190041
Ayush Anand
200238
Mobashsharah Ali
200585
Yash Manihar
201145
Objective
To study the diffusion coefficient for a liquid mixture of CCl4 and
Ethanol
Aim
To determine the diffusion coefficient of an organic vapour mixture (CCl4 and
(C2H5OH) in air at fixed T=55˚C
Introduction
-> Diffusion is concerned with the movement of individual molecules through
a substance by virtue of their thermal energy.
-> The phenomenon of molecular diffusion ultimately leads to a completely
uniform concentration of substances throughout a solution that may initially
have been non-uniform.
Theory
-> If two gases are inter-diffusing with continual supply of fresh gas
and removal of the products of diffusion, this diffusion reaches an
equilibrium state with constant concentration gradients.
-> This is known as steady state diffusion. If also there is no total flow
in either direction, the diffusion rates of A+B and B, NA and NB are
equal but have opposite signs.
Description of the experiment
The equipment consists of a T tube made of glass, placed in a constant
temperature water bath. The temperature of the bath is controlled by the
DTC. An air pump is used to supply the air, passed through the T tube. The
volatile component is filled in the T tube and air is passed over it by the
pump and a change in the level is seen by the sliding microscope.
Nomenclature Used
Formulas Used
Data used
Apparatus and Utilities Required
●
Electricity Supply: Single phase, 220 VAC, 50 Hz, 515 A Socket with earth connection.
●
Floor Area Required: 1.5 m x 0.75 m
●
Required Chemicals & Laboratory Glassware
Procedure
● Clean the apparatus and make it free from dust.
● Fill 3/4th water bath with water.
● Set the water bath temperature at 55˚C and wait till the bath attains the set
temperature. Note the steady temperature of the bath.
● Fill the T-tube with liquid mixture up to within two centimetres of the top of
capillary leg. Note down the initial diffusion height of liquid in the capillary.
● Make the connection with the Air or vacuum pump and allow a gentle current of
air to flow over the capillary.
● Record the height of liquid (x) in the capillary after every 15 min manually and
through camera through computer
● Repeat the steps 1 through 5 for different compositions.
Observations
Calculations
Graphs
Graphs
Graphs
Graphs
Results and Discussion
1) In the D vs z curve, we observe the value of D goes from 5.91 x 10-3 cm2
/s for pure CCl4, minimum at 4.04 x 10-3 cm2 /s for 0.6 mol fraction CCl4
and then 9.3 x 10-3 cm2 /s for pure C2H5OH
2) Though the accuracy of the vernier scale is 0.001mm, the human eye
resolution is not so accurate, and the factor of human error is present in
the observations.
3) The possibility of turbulent flow and a quicker rate of mass transfer exists
if air is blown through at a faster speed.
Conclusion
1)
Mixing property and volatility of mixture may have affected D.
2)
One possible reason for observing the trend may be that we took the assumption of an ideal
gas mixture and that equilibrium is reached by the mixture and maybe the situation may
better be described by nonequilibrium mechanics, hence deviation from these assumptions
may explain the observed behavior of lowering of Diffusion coefficient at high mixing.
3)
Since the involved species is three the assumptions in derivation may not apply
straightforwardly as in the case of single species diffusion.
Remark on experimental apparatus
We took the readings from the manual scale
and as seen in the image attached, 50 exact
divisions of the Vernier scale correspond to 49
main scale divisions, hence the readings would
be reliable and precise.
Remark on experimental apparatus
We see when VS and MS 0 coincide
no other division on VS matches
MS, this problem was also seen in
regular lab experiments hence we
didn’t choose this as it may lead to
a high degree of unreliability and
loss of precision.
References
1. McCabe, Smith, “Unit Operations of Chemical Engineering”, 7th
ed, McGrawHill, NY, 2005, Page 528, 531-532.
2. Binay K.Dutta, “Principles of Mass Transfer and Separation
Processes”, Prentice Hall of India Pvt Ltd., ND, 2007, Page 11-15
3. Data obtained by Peng-Robinson 78 Model and Antoine
Equation from Chemsep.
Thank You