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Diffusion Tube Assignment (mass method, 1 tube) In this experiment you will be taking data to compute the diffusion coefficient of cyclohexane and perhaps acetone in air, comparing the results to predicted and literature values, and discussing the possible sources of discrepancies between values. Meet with the TA to discuss plans for recording data- you should all take turns getting data throughout the day on ___________ and ___________. Procedure: 1) Measure the initial diffusion path length. 2) Record the mass of the tube and air temperature at time zero. Note what air currents are in the room and how exposed the tube is to these currents. 3) Record mass and temperature approx. every hour for 8-10 hours Analysis: 1) Plot your data by modifying equation 6.26-26 in such a way that all of the time data is used and the diffusion coefficient may be obtained from the inverse slope. Is the data linear- are there any patterns? Why or why not? How long would you expect it to take for the system to come to steady state? What does scatter in the data represent? Use linear regression and statistical output (Excel or Polymath) to estimate the uncertainty in the value of diffusivity based solely on the the assumption of random scatter in the data. 2) Calculate the expected value of diffusivity using both the ChapmanEnskog equation (6.2-44) and the Fuller, Schettler and Giddings method.(eqn. 6.2-45, table 6.2-2). 3) Compare your experimental value of the diffusivity coefficient with the estimated values from number 2 above, as well as with the literature value for air-cyclohexane and air-acetone. Are the results consistent? What degree of accuracy would you expect using those equations? 4) What uncertainties are present as a result of the methods and materials you used to measure the diffusion coefficient? 5) What assumptions were made in the derivation of equation 6.2-26? How does the method outlined in the Lee and Wilke paper correct for some of the “non-idealities” of the system? (explain fully). 6) Was the initial height of the liquid in the tube chosen wisely? Why or why not. References: 1) Transport Processes and Separation Processes, 4th ed. by Geankoplis (esp, sect. 6.2C) 2) Perry’s Handbook 3) CRC or Lang’s Chemical Handbook or similar 4) Lee, C.Y. and Wilke, C.R., Industrial and Engineering Chemistry, Nov. 1964 5) Any other library or on-line references you think will be of help 6) Handouts from class