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Chemistry 1201 Section 4
Spring 1999
Professor Russo
Exam #3
Type of exam: Take-home. You can work with anyone on this exam, including me! You
better know how to do these problems, though. You will probably see similar problems again.
Due: Tuesday, February 23 at the beginning of class.
100 points. Show your work neatly. We will not grade papers that just show an answer,
nor can we assign partial credit if we don't see the work.
________________________________________________________________________
Question #1. (BLB Text 2.16) Fill in the table.
70
Symbol
Ga
Protons
23
Neutrons
28
Electrons
45
34
136
79
Atomic No.
86
Mass No.
197
Question #2. (BLB Text 2.56 --Oh dear, yet another density problem! But this density is
unusual). Using the mass of the proton from Table 2.1 and assuming its diameter is
1.0 x 10-15 m, calculate the density of a proton in g/cm3. About what fraction of water is
actually empty space?
__________________
Put the density here
Chem 1201 Sec. 4
__________________
Put the empty fraction here
Exam #3
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Question #3. (based on BLB Text 2.61; see the FAQ page on the website for help. This
question is phrased more directly than the one in your book, but it is essentially the same
problem. It is a very important, basic type of problem since this is how much of what we know
about chemical matter was determined).
Butane contains 82.8 % carbon by weight and hydrogen as the only other element. For
example, a 2.503 g sample of butane contains 2.072 g of carbon. Determine the empirical
formula of butane. Hint: another hydrocarbon called acetylene is found to contain 92.3%
carbon by mass. Of all hydrocarbons, acetylene has the highest percentage of carbon.
__________________
Put your answer here
Question #4. (BLB 6.8a) What is the frequency of the radiation whose wavelength is 1.73
nm? What kind of radiation do we call this?
___________________
Put the frequency here
Chem 1201 Sec. 4
Exam #3
__________________
Put the type of radiation here
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Question #5. (based on BLB #6.14) What is the smallest increment of energy in calories that
can be emitted or absorbed at a wavelength of 146 nm?
__________________________
Put your answer here
Question #6. (BLB 6.20) A certain photographic film requires a minimum radiation energy of
80 kJ/mol to cause exposure. What is the longest wavelength, in meters, of radiation that
possesses the necessary energy to expose the film? Could the film be used for infrared
photography?
______________________
Put Longest Wavelength Here
Yes, OK No, Not OK
Circle One
Question #7. (BLB Text 6.32b) The hydrogen atom can absorb light of wavelength 1282 nm.
Determine the initial and final values of n associated with their absorption.
nfinal:__________
Chem 1201 Sec. 4
Exam #3
ninitial_________
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Question #8. (BLB Text 6.36) When an electron in an electron microscope is accelerated
through 100 V, it attains a speed of 5.93 x 106 m/s. Determine the characteristic wavelength of
this electron in Å. Is that wavelength comparable to the size of atoms?
____________________
Write wavelength here
Yes, comparable
No, not
Circle One
Question #9. (similar to BLB 6.75, which was not assigned--sorry). The little red laser
pointer that I use in class produces about 5 mW at 670 nm. How many photons will it emit in
15 s? Express your answer in mol.
__________________
Put your answer here
Question #10 (BLB 6.77). Chorophyll absorbs blue light,  = 460 nm, and emits red light,  =
660 nm. Calculate the net energy change in the chlorophyll system (in kilojoules) when a mole
of 460-nm photons is absorbed and a mole of 660-nm photons is emitted.
________________________
Put Answer Here
Chem 1201 Sec. 4
Exam #3
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