Relative rates of effusion through punctured balloons

Graham's Law and Perpetuation of Error

“…Errors taught in introductory chemistry are passed on to the student's students' students. This is illustrated by two recent contributions (1,2) to this Journal. Graham's law of diffusion applies only to gases that are diffusing into each other, so it does not apply to the case in ref 1 comparing the rates of diffusion of HCl and an amine vapor by the relative distances they diffuse in air, paralleling the well-known erroneous demonstration with HCl and NH 3 .…”

“…As calculated above, the ratios of HCl to methylamine or dimethylamine should be 1.04 or 0.96 compared to 1.09 or 0.90 from misinterpretation of Graham' s law or to the 1.0 or 0.91 the authors found experimentally (1). When ammonia is used, the ratio is 1.23 calculated as above (or 1.28 if the cross sections are allowed for [2]) instead of the 1.47 from misusing Graham's law; so the customary demonstra-…”

“…(neglecting the correction for unequal cross sections). The quantities in parentheses do not cancel to leave Graham's ratio unless the molecular weights of the amine and HCl are equal (2). Ammonia fails because its molecular weight, 17, is very different from the 36.5 of HCl, but the two amines used in (1) are closer to 36.5 so that the misinterpretation of Graham's law is not so obviously disobeyed.…”

A Balloon Filled with Nitrogen Gas Does Not Satisfy the Air- or Moisture-Free Reaction Condition

“…8 The theoretical permeation rate of CO2 was estimated as about 1.5 times slower than that of H2O. Grignard reagents can react with CO 2 to be converted into the corresponding carboxylic acids.…”

Balloon—Toy of Many Colors

“…Articles on balloons have appeared in JCE since the 1930s. Many of these describe experiments and demonstrations to teach gas law concepts: Charles' Law (4-6), molar mass (7), Graham's Law (8), and Avogadro's Law (9). A series of three papers (10)(11)(12) describing experiments relating PV work and the energy needed to increase the surface area of the balloon will interest faculty teaching physical chemistry.…”