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Study Guide Answers
Chapter 21
AP Chemistry
1. The splitting of the nucleus into lighter nuclei is called fission .
2. When light mass nuclei combine to form a heavier, more stable nucleus this is called fusion .
3. Write an equation for the alpha decay of bismuth-213. 21383Bi ๏ฎ 42He + 20981Tl .
4. Write an equation for the beta decay of silver-106. 10647Ag ๏ฎ 0-1e + 10648Cd .
5. Describe the difference between beta decay and electron capture. In beta decay, an electron is emitted from the
nucleus as a neutrons transforms into a proton. In electron capture (or K capture or beta capture) an electron is taken in
from the electron cloud by the nucleus to convert a proton into a neutron. .
6. The mass of a lithium-7 atom* is 7.01600amu. Calculate it mass defect.
p+ mass = 3 x 1.007276 amu = 3.021828 amu
no mass = 4 x 1.008665 amu = 4.034660 amu
e- mass = 7 x 0.0005486 amu = 0.0016458 amu (* mass is for atom, not nucleus)
Theoretical Mass = 7.0581338 amu
Mass defect = 7.0581338 amu โ 7.01600 amu = 0.04213 amu
7. Calculate the nuclear binding energy of one lithium-6 atom. The actual measured atomic mass of lithium-6 is 6.015amu.
p+ mass = 3 x 1.007276 amu = 3.021828 amu
no mass = 3 x 1.008665 amu = 3.025995 amu
e- mass = 7 x 0.0005486 amu = 0.0016458 amu (* mass is for atom, not nucleus)
Theoretical Mass = 6.0494688 amu
Mass defect = 6.0494688 amu โ 6.015 amu = 0.0344688 amu (must be expressed in kg to use E=mc2)
0.0344688 amu
1 gram
1 kilogram
= 5.723812687 x 10-29 kg
6.022 x 1023 amu
1000 grams
E = mc2 = 5.723812687 x 10-29 kg โ (3.00x108m/s)2 = 5.15x10-12J
Since I used 3 sig figs for โcโ, I rounded the final answer to 3 sig figs.
8. Oxygen has an unstable isotope O-17 that has a mass of 17.00454. Calculate the binding energy of the oxygen nucleus in
MeV.
p+ mass = 8 x 1.007276 amu = 8.058208 amu
no mass = 9 x 1.008665 amu = 9.077985 amu
e- mass = 8 x 0.0005486 amu = 0.0043888 amu (* mass is for atom, not nucleus)
Theoretical Mass = 17.1405818 amu
Mass defect = 17.1405818 amu โ 17.00454 = 0.1360418 amu (must be expressed in kg to use E=mc2)
0.1360418 amu
1 gram
1 kilogram
= 2.25908004 x 10-28 kg
6.022 x 1023 amu
1000 grams
E = mc2 = 2.25908004 x 10-28 kg โ (3.00x108m/s)2 = 2.03382036x10-11J
1eV = 1.60 x 10-19 joules (Iโd give this value to you in the test.)
2.03382036x10-11J
1 eV
1 MeV
= 127 MeV
1.60 x 10-19 J
1000 000 eV
Since I used 3 sig figs for โcโ and the eV conversion, I rounded the final answer to 3 sig figs.
Proton Mass 1.007276amu
Neutron Mass 1.008665amu
Electron Mass 0.0005486amu
