University Chemistry: Nuclear Chemistry Worksheet and Solutions

This chemistry assignment is a comprehensive worksheet exploring the concepts of nuclear chemistry. It covers a range of topics including calculating the number of protons and neutrons in various isotopes, writing balanced nuclear equations for alpha and beta decay, positron emission, and electron capture. The worksheet delves into identifying different types of nuclear decay, predicting decay modes based on nuclear composition, explaining the belt of stability, and working through half-life calculations using both approximations and equations. Additionally, the assignment includes questions on critical mass, the energy released in nuclear reactions, and the mass defect. The solutions provided offer a detailed understanding of the principles of nuclear chemistry and provide a valuable resource for students studying this subject.

Week 6 Worksheet
1. How many protons and neutrons are in: 55Mn, 201Hg, potassium-39, barium-141?
55Mn,
Number of protons: 25
Number of neutrons: 55 - 25 = 30
201Hg,
Proton: 80
Neutrons: 201-80 = 121
Potassium-39:
Protons: 19
Neutrons: 39 - 19 = 20
Barium-141:
Protons: 56
Neutrons: 141 - 56 = 85
2. How many protons and neutrons are in 60Co, 238U, thorium-232, radon-220?
60Co
Protons: 27
Neutrons: 60-27 =33
238U
Protons: 92
Neutrons: 238-132 = 146
thorium-232
Protons: 90
Neutrons: 232-90 = 142
radon-220
Protons: 86
Neutrons: 220-86 = 134

3. Write balanced equations for: bismuth-214 undergoes beta decay, plutonium-242
emits alpha radiation, selenium-81 undergoes beta decay, uranium-235 undergoes alpha
decay, 11C emits a positron, O-15 undergoes electron capture
Plutonium-242 emits alpha radiation:
Bi83
214 → Po+ e1
0
84
214
Plutonium-242 emits alpha radiation:
Pu94
238 → U92
238 + He2
4
Selenium-81 undergoes beta production
Se34
81 → Br+ e1
0
35
81
Uranium-235 undergoes alpha decay:
U92
235 → Th+ He2
4
90
231
11C emits a positron:
C6
11 → β+ e1
0
5
1 1
O-15 undergoes electron capture:
O+ e1
0 → N7
15
8
15
4. Write balanced equations for: 241Am emits alpha radiation, chromium-51 undergoes
electron capture, 99Tc emits a gamma particle, fluorine-18 emits a positron, 124Sb emits a
beta particle.
241Am emits alpha radiation:
Am → Np97
237
95
241 + He2
4
Chromium-51 undergoes electron capture,
Cr+ e1
0
24
51 → Mn25
51
99Tc emits a gamma particle:
Tc →43
99 m Tc+γ43
99 m

Fluorine-18 emits a positron
F → O+ e1
0
8
18
9
18
124Sb emits a beta particle.
Sb → Te+ β−1
0
52
124
51
124
5. What kind of nuclear decay/capture is each of the following (write equations and
name process): I-131 to Xe-131, Ra-226 to Rn-222, Rb-81 to Sr-81, Hg-201 to Tl-201,
Th-231 to Ra-227, N-13 to C-13, Pu-242 to Pu-242, Be-7 to Li-7
6. What kind of nuclear decay/capture is each of the following (write full equations and
name process):
216Rn  42He + ____ alpha decay
___  42He + 239Bk alpha decay
40K  40Ca + ___
40K + ___  40Ar
40K  40Ar + ___
60Co  60Co + ___
7. What kind of decay, and why, would you expect from each of the following? Note that
if you look these up on the internet, you may find that each decays by more than one
mechanism. The only correct/acceptable answers will be those that could be reasonably
predicted based upon nuclear makeup.
35S

226Ac
11C
52Ti
257Md
15O
8. Explain the belt of stability in words (do not quote from lecture or copy from any other
source). Cover the following: why are n:p ratios 1:1 for smaller nuclei and >1:1 for larger
nuclei? How are nuclei above the belt of stability likely to decay, and why? How are
nuclei below the belt of stability likely to decay, and why? Why are elements larger than
Pb radioactive? What is likely to be among the decay modes of these large nuclei, and
why?
9. What is the product when Th-228 decays by: alpha, alpha, alpha, alpha, beta, beta
(write out equations).
10. The half-life of tritium is 12.3 years. What mass of a 48.0g sample remains after 24.6
years? Answer using approximations, giving your best educated guess for answer (do not
use equations).

11. The half-life of tritium is 12.3 years. What mass of a 48.0g sample remains after 24.6
years? Answer using equation(s).
12. The half-life of tritium is 12.3 years. How long does it take for a 48.0g sample to be
reduced to 2.0g? Answer using approximations, giving your best educated guess for
answer (do not use equations).
13. The half-life of tritium is 12.3 years. How long does it take for a 48.0g sample to be
reduced to 2.0g? Answer using equation(s).
14. A radioactive sample of 100. g has been reduced to 1.56g in 85 years. How long is
the half-life? Answer using approximations, giving your best educated guess for answer
(do not use equations).
15. A radioactive sample of 100. g has been reduced to 1.56g in 85 years. How long is
the half-life? Answer using equation(s).
16. 13N decays with a half-life of approximately 10 min to produce 13C, a stable isotope of
carbon. For a 1.0g sample of 13N, after one half-life, what mass of 13N remains? What has
happened to the remaining mass?

17. 223Ra decays by alpha emission with a half-life of 11.43 days. For a 1.0g sample of
223Ra, after one half-life, what mass of 223Ra remains? What has happened to the
remaining mass?
18. Define and explain critical mass.
A critical mass is the smallest amount of fissile material needed for a sustained nuclear
chain reaction.
19. Why is the neutron-induced fission of U-235 potentially self-sustaining?
20. A reaction takes place with a mass defect of 0.030kg. How much energy does this
correspond to?
E=mC2
E=1 amu ¿

21. How much mass defect is required to release 5.5 x 1020 J of energy?
22. A reaction of 2.5kg of fissionable material takes place. Assuming a 0.10% mass
defect, how much energy is released?