Ch186 Nuclear Chemistry Exam Questions From Spring 2001 Semester Useful constants

CH186

Nuclear Chemistry Exam Questions

From Spring 2001 Semester

Useful constants:
Avogadro’s number (N_A) = 6.022137 x 10²³/mol

mass of proton = 1.007276 amu

mass of neutron = 1.008664 amu

mass of electron = 5.485799 x 10^-4 amu

speed of light (c) = 3.0 x 10⁸ m/s

6.022137 x 10²³ amu = 1g

1 J = 1 kgm²/s²

1 eV = 1.602 x 10^-19 J

1 Mev = 10⁶ eV
1) Complete and balance each of the following nuclear reactions.
a.
b.

c. 

d.
e.
2) Predict the most likely type of radioactive decay process for each of the following radionuclides. In each case, decay occurs only via beta emission, alpha emission, or positron emission.

a. (All isotopes of thorium are radioactive.) ___________________

b. ( is stable and nonradioactive.) ____________________
c. ( is stable and nonradioactive.) ____________________
d. ( is stable and nonradioactive.) ____________________
e. ( is stable and nonradioactive.) ____________________

3) Write balanced nuclear equations for each of the following processes.

a. bombardment of curium-246 (Cm) with carbon-12 produces nobelium-252 (No) and neutrons

b. positron emission by iron-53 (Fe)

c. electron capture by tellurium-111 (Te)

d. alpha emission by lawrencium-259 (Lr)

e. beta emission by platinum-201 (Pt)
4) In each of the following pairs, one of the nuclides is radioactive and the other is stable and nonradioactive. Predict which is radioactive and which is stable, and explain your choice briefly.
a. Y-90 or Zr-90

b. Cr-52 or Cr-49

5) Linen wrapped around the mummy of the great King Perseus of the ancient kingdom of Orangello gave 12.8 disintegrations of ¹⁴C per minute per gram of carbon. Assuming that the linen was less than a year old when used in the burial of the king, approximately how many years ago did the old boy die? Carbon from present-day living material gives 15.3 disintegrations of ¹⁴C per minute per gram of carbon. The half-life of carbon-14 is 5.715 x 10³ years.
6) The decay constant of gallium-67, a radioisotope used for imaging soft-tissue tumors, is 0.00886/hr (hr^-1). Calculate the half-life, t_1/2, in seconds (s) for ⁶⁷Ga.
7) Calculate the mass defect for palladium-106. The atomic mass of the ¹⁰⁶Pd nucleus is 105.87824 amu. Account briefly for the difference in mass observed.
8) Consider the fission reaction in which uranium-235 is bombarded by neutrons.
n + U  Rb + Ce + 3e + 3n
The atomic masses (in amu) are 235.043924 for uranium-235, 88.912278 for rubidium-89, 143.913643 for cerium-144, 5.485799 x 10^-4 for the electron (e), and 1.008664 for the neutron. Calculate the amount of energy released, E ( in kJ), when one gram of uranium-235 undergoes this fission reaction.
9) A sample of phosphoric acid, H₃PO₄, known to contain a significant amount of radioactive phosphorus-32, was accidentally spilled onto the lab floor. It was suggested by one of the technicians in the lab that the radioactivity could be neutralized by reacting the spilled acid with a base such as NaOH. Do you agree or disagree with this suggestion? Explain your answer.

Answers for Spring 2001 Nuclear Chemistry Exam Questions
1. a.

b.

c.
d.
e.
2. a. alpha

b. beta

c. positron

d. beta

e. positron
3. a.
b.
c.
d.
e.
4. a. Zr-90 is nonradioactive and Y-90 is radioactive. This is based on the fact that Zr-90 has a magic number of neutrons (50) and even numbers of both protons (40) and neutrons (50), whereas Y-90 does not.

b. Cr-52 is nonradioactive and Cr-49 is radioactive. This is based on the fact that Cr-52 has a magic number of neutrons (28), whereas Cr-49 does not.

5. 1471 years

6. 2.82 x 10⁵ seconds

7. 0.9763 amu

8. -7.62 x 10⁷ kJ/g

9. Disagree. Nuclear reactions take place inside the nucleus and involve changes in the nucleons. Chemical reactions take place outside the nucleus and involve valence electrons. Thus, the reaction suggested by the technician will only neutralize the acidity of the spilled acid, not the radioactivity of the P-32 in it. Nuclear reactions occur regardless of the chemical state of the radioactive atom.

Nuclear Chemistry Exam Questions

From Fall 1999 Semester
Useful constants:
Avogadro’s number (N_A) = 6.022137 x 10²³/mol

mass of proton = 1.007276 amu

mass of neutron = 1.008664 amu

mass of electron = 5.485799 x 10^-4 amu

speed of light (c) = 3.0 x 10⁸ m/s

6.022137 x 10²³ amu = 1g

1 J = 1 kgm²/s²

1 eV = 1.602 x 10^-19 J

1 Mev = 10⁶ eV
1) a. Complete and balance each of the following nuclear reactions.
N + Cf  __________ + 4n
As  __________ + Se
__________  Cf + He
Co  __________ + e
b. Write balanced nuclear equations for each of the following processes.
electron capture by

beta emission from

positron emission from

alpha emission from

2) Strontium-90 is one of the most hazardous products of atomic weapons testing because of its long half-life (t_1/2 = 28.1 years) and its tendency to accumulate in bones. Calculate the decay constant of this isotope in reciprocal minutes, i.e. min^-1 or 1/min?
3) An oil painting alleged by a dealer to be painted by Rembrandt (1606-1669) is subjected to carbon-14 dating. The canvas of the painting shows an average of 14.68 disintegrations/min per gram of carbon. The carbon in living organisms today undergoes an average of 15.3 disintegrations/min per gram. If the half-life of carbon-14 is 5730 years, could this painting be an original Rembrandt? Show your calculations to prove your answer.

4) A typical induced fission reaction is

n + U  Te + Zr + 2n
Calculate the energy released by the overall fission reaction in kJ per gram of uranium-235. The atomic masses are: U = 235.0439 amu, Te = 136.9254 amu, Zr = 96.9110 amu.
5) Chemical reactions can often be used to change a toxic chemical into another compound that is not as toxic. Why can’t chemical treatment technology be applied to make radioactive nuclear waste harmless? Explain!


Answers for Fall 1999 Nuclear Chemistry Exam Questions
1 a. Unp

e

Fm

Fe
b. Ca + e  K

Sb  e + Te
Cu  e + Ni

Fm  He + Cf
2. 4.68 x 10^-8/min

3. t = 342 years, yes

4. -7.62 x 10⁷ kJ/g

5. Chemical reactions involve the valence electrons and bond-making/bond-breaking. However, nuclear reactions take place in the nucleus of an atom. The nuclear reactions of an isotope are the same regardless of its chemical form.