What Could Cause Large Percent Deviation in Graham's Law Experiment?

[BayernBlues]

Homework Statement

This is for an experiment. I determined the theoretical diffusion ratio of ammonia to hydrogen chloride to be 1.46:1 but my experimental error to be 4.20:1. This means that my percent deviation was around 200%. Question is, what are the reasons for the large percentage deviation.

2. The attempt at a solution

I know that one reason is obviously a reading error, but what about other stuff like non ideal gas behaviour, how would I elaborate on that?

 

[chemisttree]

Please elaborate on the method and your calculation.

 

[erjkism]

did you use a large glass tube for the experiment? if you did, the length of the tube might have something to do with it. a really short tube would make measurements difficult.