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?

 

[DeeNos]

it

Thank you for sharing your experiment and results. It is clear that you have put effort into designing and conducting your experiment. However, I would like to offer some suggestions for improvement.

Firstly, it is important to clearly state the purpose of your experiment. In this case, it seems that you are trying to determine the diffusivity of HCl in air. It would be helpful to explain why this information is important or relevant to your research or field of study.

Additionally, it would be helpful to provide more details about your experimental setup. For example, what type of glass tube did you use? How was the temperature of the air inside the tube measured and controlled? How was the concentration of HCl in the cotton piece determined? These details can help readers understand the reliability and accuracy of your results.

Furthermore, it would be helpful to include a control group in your experiment. This could be a tube with just air (no HCl) to compare the movement of the indicators and the time it takes for the litmus papers to change color. This can help to rule out any external factors that may have influenced your results.

In terms of the model you used, it is important to choose a model that is appropriate for your experiment and has a clear connection to your research question. It seems that the Skellam model you initially used is not suitable for this experiment. I would suggest consulting with a mentor or conducting further research to find a suitable model for your experiment.

Overall, your experiment is a good starting point but there are some areas for improvement. I would recommend revisiting your research question and experimental design to ensure that your results are reliable and accurately reflect the diffusivity of HCl in air.