In this experiment, students build
a spectrometer to explore infrared
radiation and greenhouse gases in an inquiry-based investigation to
introduce climate science in a general chemistry lab course. The lab
is based on the exploration of the thermal effects of molecular absorption
of infrared radiation by greenhouse and non-greenhouse gases. A novel
feature of the experiment has students building an infrared spectrometer,
using a hot plate as an IR source, a sample compartment employing
a plastic cuvette holder with open sides (to standardize the path
length), and a low-cost infrared thermometer. Students, working in
groups, (1) explore a PhET simulation; (2) design a set of experiments
in response to a scientific question, “comparing the absorption
of infrared light in the presence and absence of each different sample
of gas, are there any significant differences that can be observed
experimentally?”; (3) reflect on climate science and their
experimental results by visiting the American Chemical Society Climate
Science Toolkit; and (4) communicate their results in lab by constructing
and presenting a poster. Assessment of student responses to a pre-
and postexperiment question suggests that the lab has a positive influence
on student understanding of the concepts involved in identifying greenhouse
gases. Results from postexperiment questions also provide information
for what aspects of the online resources students found useful.
The mechanism of gold(i)-thiolate, disulfide exchange was investigated by using initial-rate kinetic studies, 2D ((1)H-(1)H) ROESY NMR spectroscopy, and electrochemical/chemical techniques. The rate law for exchange is overall second order, first order in gold(i)-thiolate and disulfide. 2D NMR experiments show evidence of association between gold(i)-thiolate and disulfide. Electrochemical/chemical investigations do not show evidence of free thiolate and are consistent with a mechanism involving formation of a [Au-S, S-S], four-centered metallacycle intermediate during gold(i)-thiolate, disulfide exchange.
Phosphine gold(I) thiolate complexes react with aromatic disulfides via two pathways: either thiolate-disulfide exchange or a pathway that leads to formation of phosphine oxide. We have been investigating the mechanism of gold(I) thiolate-disulfide exchange. Since the formation of phosphine oxide is a competing reaction, it is important for our kinetic analysis to understand the conditions under which phosphine oxide forms.
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