(a) A research chemist used a mass spectrometer to study the two isotopes of
an element. Over time, she recorded a number of mass spectra of these
isotopes. On analysis, she noticed that the ratio of the taller peak (the more
abundant isotope) to the shorter peak (the less abundant isotope) gradually
increased with time. Assuming that the mass spectrometer was functioning
normally, what do you think was causing this change?
(b) Mass spectrometry can be used to identify the formulas of molecules having
small molecular masses. To illustrate this point, identify the molecule which
most likely accounts for the observation of a peak in a mass spectrum at: 16
amu, 17 amu, 18 amu, and 64 amu.
(c) Note that there are (among others) two likely molecules that would give
rise to a peak at 44 amu, namely, \(\mathrm{C}_{3} \mathrm{H}_{8}\) and
\(\mathrm{CO}_{2}\). In such cases, a chemist might try to look for other peaks
generated when some of the molecules break apart in the spectrometer. For
example, if a chemist sees a peak at 44 amu and also one at 15 amu, which
molecule is producing the 44 -amu peak? Why?
(d) Using the following precise atomic masses:
\({ }^{1} \mathrm{H}(1.00797\) amu \(),{ }^{12} \mathrm{C}(12.00000
\mathrm{amu}),\) and
\({ }^{16} \mathrm{O}(15.99491 \mathrm{amu}),\) how precisely must the
masses of \(\mathrm{C}_{3} \mathrm{H}_{8}\) and \(\mathrm{CO}_{2}\) be measured to
distinguish between them?
(e) Every year millions of dollars' worth of gold is stolen. In most cases the
gold is melted down and shipped abroad. This way the gold retains its value
while losing all means of identification. Gold is a highly unreactive metal
that exists in nature in the uncombined form. During the mineralization of
gold, that is, the formation of gold nuggets from microscopic gold particles,
various elements such as cadmium (Cd), lead (Pb), and zinc \((\mathrm{Zn})\) are
incorporated into the nuggets. The amounts and types of the impurities or
trace elements in gold vary according to the location where it was mined.
Based on this knowledge, describe how you would identify the source of a piece
of gold suspected of being stolen from Fort Knox, the federal gold depository.
Explanations 
Textbooks 
Flashcards 
91影视 AI 
Notes 
Study Plans 
Study Sets 
Find a degree 
Magazine 
