The herbicide paraquat, N, N'-dimethyl-4,4'-bipyridiunium dication (N,N'-methyl viologen), is electrochromic. Experiments are described that investigate its redox chemistry (cyclic voltammetry), its optical properties (photometry and UV/Vis spectrophotometry), and its potential as a system for electrical "photoswitching" and as an accumulator for rechargeable devices. This set of teaching laboratory experiments closely reflects true procedures in commercial research and development endeavors, because the same system is probed with several quite different, but complementary, analytical methods.
The physical properties of oxygen, in particular, the
blue color of the liquid phase, the red glow of its chemiluminescence,
and its paramagnetism as shown by the entrapment or deflection of
liquid oxygen by a magnetic field, can be investigated in a regular
school setting with hand-held spectrophotometers and digital cameras.
In college-level chemistry courses, the paramagnetic property often
serves as a dramatic illustration of the usefulness of molecular orbital
(MO) theory. However, MO treatment of oxygen molecules alone cannot
explain the observed photon absorptions and emissions. In fact, it
is the formation of oxygen dimers (O2)2 that accounts for the observed optical phenomena and is also
responsible for the “not-quite-right” degree of deflection
of the liquid stream of oxygen near a magnet. A review of experimental
and theoretical studies of O4 and (O2)2 suggests that the so-called one-photon-two-O2-molecule
mechanism be considered a one-photon-one-O2-dimer process.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.