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NAME ____________________________________________ GRADED: LET IT BEGIN!!!
____ / 30 pts
DIRECTIONS: Use your summer work, your overall grasp of chemistry, and the reading of technical writing and concept
mapping to complete the following questions. Please download a copy of this from my website and word process your
short answer responses to question 1. All other work may be in your handwriting. Thank You ….The Management.
Necessary Background: When an isotope is a nuclear radioactive isotope, it means that it can spontaneously
breakdown, by emitting alpha particles (effectively He-4 nuclei each equaling 2 protons and 2 neutrons, and of
course, 0 electrons), beta particles (high speed e- from degenerating neutrons) or gamma rays (high frequency
energy). A radioactive isotope can spontaneously transmute into (turn into) an isotope of another element when
these changes to the nucleus, changes the number of protons!
Nuclear fission is a nuclear reaction in which a heavy nucleus (such as uranium) splits into two or more, lighter
nuclei. As this splitting (transmutation) occurs, new, smaller / different isotopes are produced and there is a
release of energy. The release of energy occurs whenever new nuclei are made, due to a mass defect and a
conversion of that lost mass to energy.
Here’s the Issue: Uranium is a highly radioactive element. Every isotope of uranium can undergo nuclear
fission, and other decay sequences. Some isotopes are more efficient at this process than others. It turns out
that U-235 is a far more fissile fuel than U-238. During WWII it became imperative to efficiently separate the
more useful (but rarer) U-235 from the more plentiful (but less useful) U-238, on a large scale.
One means of this separation begins by converting solid yellowcake ore (U3O8) to UF4, a green solid compound
with a normal boiling point of 1,415 °C. The UF4 is then converted to the easily vaporized UF6, with a normal
boiling point of only 56.5 °C. Once vaporized, gaseous diffusion is used to separate the molecules of UF6 made
with U-235 and U-238, thereby concentrating (purifying) a samples of made with U-235.
It is important to note that fluorine has only a single naturally-occurring stable isotope, so differences in the
mass of molecules of UF6, made with U-235 and U-238, are due solely to the uranium isotope present. This
made gaseous diffusion an efficient means of separating molecules of UF6 with the more fissionable
uranium-235 from the more plentiful, but less fissile, uranium-238.
The Lewis structural formula of UF6 is:
1) An AP student recalled from their first year course that as the oxidation state of a metal increases, so does
the degree of covalent bonding. When the oxidation state of the metal is highly positive (roughly +4 or
larger) we should expect a significant covalent nature in the bonds formed with nonmetals (as opposed to
ionic bonding).
a) A student argued that the name of UF6 should be uranium hexafluoride. Her lab partner disagreed and
suggested the name uranium(VI) fluoride would be more correct.
Using your grasp of the summer work, and this worksheet, take a stand on the name of UF6 and defend
your reasoning in a well-developed short answer. (Please word process) (1 pt answer, 4 pts defense/supporting argument(s)/organization)
b) Given the polyatomic ion, dichromate, would you expect the bonding between the chromium and oxygen
to be ionic or covalent? Defend your reasoning. (Please word process) (1 pt answer, 4 pts defense/supporting argument(s)/ organization)
2) a) Write the balanced chemical reaction equation for conversion of U3O8 (a form of milled oxide ore, called
yellowcake to UF6, water and UO2. To achieve this conversion, the yellowcake is reacted with HF. (2pts)
b) Assuming 500.0 grams of U3O8 are available, how many kilograms of HF would be required to
consume the yellowcake mass completely? (Show your work, using unit cancellation and sig figs for partial credit) (2 pts)
c) Why was it desirable to produce UF6? Why didn’t chemists simply use the more common UF4 to
help in the separation of compounds containing the different uranium isotopes? (2 pts …Use APS)
d) Based upon your grasp of laboratory techniques, would
you claim that gaseous diffusion is a physical
process or a chemical process? ________________________
(1 pt)
e) The density of UF6 is 5.09 g/cm3. The molar mass of UF6 equals 352.02 g/mol. What would the density
of 0.500 mol of UF6 equal? _________________g/cm3 (1 pt)
f) Using your understanding of intensive and extensive properties, defend your response to 2e). (2 pts Use APS)
3) Based upon the summer work, what is the most proper name for UO2? ________________________ (1 pt)
4) Based upon the summer work, what is the formula for gold(I) sulfide? ________________________ (1 pt)
5) With how many significant figures should the solution to: 320.55 - (6104.5/2.3) be recorded? _____ (1 pt)
6) a) It is estimated that uranium is relatively common in the earth's crust, occurring in amounts of
4.0 g / metric ton. A metric ton is equivalent to 1000. kg. At this concentration, what mass of uranium, in
grams is present in 1.5 mg of the earth's crust? (Show your work, using unit cancellation and sig figs for partial credit) (2 pts)
____________ grams
b) With how many significant figures should your answer to 6a) be recorded? ________
(1 pt)
7) Select 1 pair of terms from the following list and use the 2 Frayer diagrams on the following pages to
compare and contrast the paired terms. (2pts per Frayer Diagram)
substance and mixture
extensive property and intensive property
chemical reaction and physical change
element and compound
ionic compound and molecular compound
dipole molecule vs. non-dipole molecule