Determining the diffusivity of HCl in air - an experiment

[hala.merghani]

we made an experiment to determine the diffusivity of HCl in air by knowing the Temperature, Distances moved by HCl molecules and correspondent times, the temperature of air inside the tube was equal to 27.8°C, and the procedure were: Five indicators (Litmus papers) were put inside the glass tube and separated by suitable distances. The distances between the indicators were measured using the ruler & were recorded. A small piece of cotton was held using a tongs and wetted with Conc. HCl from the burette. The cotton was placed inside the tube and immediately the tube was closed. At the same instant of putting the piece of cotton inside the tube, the stop watch was started. The time each piece of litmus started to turn its color from blue to red was recorded. The distance between the cotton & the first litmus was measured and recorded. When the last paper’s color changed, the cotton was removed from the tube, we obtained this results:

distance(cm)______________time (sec)
12_______________________79.8
27_______________________320.75
33.5_____________________510.14
42.5_____________________705.45
52.5_____________________923.87

we used a model by John Gordon Skellam; DAB = z^2/(π^2*t), but then I've found out that this model is a reaction-diffusion model of invasion biology, which has nothing to do with our experiment, I've been searching the internet and some books from my library for quiet a while for another simple model to use, but I haven't found anything helpful, and its also required to show a whole background about the model and who invented it and how

 

[NascentOxygen]

It sounds like an interesting experiment. Are others in your class also searching for an applicable model for this? Has their search been any more fruitful?

Would it be diffusion entirely due to Brownian motion?

 

[hala.merghani]

yes the others are also searching for an applicable model, but non of the people I know could make it any further

 

[NascentOxygen]

Try asking on the chemistry sub-forum https://www.physicsforums.com/forumdisplay.php?f=83 to see whether anyone there knows of a model for diffusion of gases.

Maybe diffusion in your expt is under the influence of both gravity and Brownian motion?