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REVIEW UNIT #16
AP CHEMISTRY
Nuclear
1. Which nuclear particle has the most energy
associated with it alpha, beta or gamma?
Gamma Particles have the highest power
2. Which has the least penetrating power?
Alpha particles are the least penetrating
3. 93.75 percent of a sample of pure 131I
decays in 48 days, what is the half-life of 131I?
(A) 6 days
(B) 8 days
(C) 12 days
(D) 14 days
(E) 21 days
If 93.75% decays that means 6.25%
remains… Make a chart
# ½ lives
0
1
2
3
4
% remaining
100
50
25
12.5
6.25
4 half-lives = 48 days
So 1 half-life =
(C) 12 days
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4. Neutron bombardment of uranium can induce the
reaction represented below. Nuclide X is which of the
following?
238 U + neutron --> X + 142 Cs
92
55
(A)9235Br (B)9435Br (C)9137Rb (D)9237Rb (E)9737Rb
• A neutron is 10n and adding to 23892 U gives
you (E)9737Rb
5. The radioactive decay of 116C to 126C
occurs by the process of
(A) beta particle emission (B) electron capture
(C) alpha particle emission (D)neutron capture
(E) positron emission
11
12 C
6
The only answer that makes sense is
adding a neutron to 116C
(D) Neutron capture
6.
6C
When 23390 Th decays, the emission consists
consecutively 2 alpha particles, then one beta
particle. The resulting stable nucleus is
(A) 20684Po (B) 23392U (C) 22989Ac
(D) 22587Fe (E) 21081Tl
233
90
Th 2 42He + 0-1e = 22587Fr = (D)
2
7. 23993Np ---> 3 beta particles + 3715 P + _____
What is the missing product in the nuclear
reaction represented above?
(A) 11842Mo
(B) 23996 Cm
(C) 20281Tl
(D) 12044Ru (E) 15278Pt
239
---> 3 0-1e + 3715 P + _____
239-37 = 202
93 +3-15 = 81
(C) 20281Tl
93Np
8. What type of decay is expected in the
following situations?
a.
Fermium- 258?
b.
Nickel-70?
c.
Oxygen-14?
a. All elements beyond Bi (Z=83) are unstable and you
expect alpha decay
b. Beta emission occurs in isotopes that have too many
neutrons ( more neutrons than protons in small
atoms) like Cobalt – 60 ( 27 protons and 33 neutrons)
c. Isotopes that have too few neutrons (like nitrogen-13)
would attain stability by electron capture or positron
emission
9. Write the decay series for 23590 Th losing 2
beta particles, then an alpha particle, 2 gamma
particles, followed by the loss of another alpha
particle and one more beta particle.
235
Th 0-1e + 235 91 Pa 0-1e + 23592U
231 Th 0 γ(no change in
2He +
90
0
numbers, only energy) + 23190 Th 00 γ +
231 Th 4 He + 227 Ra 0 e + 227 Ac
90
2
88
-1
89
90
4
3
10. The half-life of cobalt-60 is 9.27 minutes.
How long before the original sample of 3.45 x
102 mmol is reduced to 1.27 x 101 mmol?
t1/2 = 9.27 minutes
A = 1.27 x 101mmol
t = ????
A0 = 3.45 x 102 mmol
k = .693/9.27minutes
k= 0.0748 min-1
ln [A/A0] = -kt
ln[1.27 x101mmol / 3.45x102mmol] = -(0.0748 min-1)t
t = 44.1 min
11. What is the half-life of a newly found
isotope is after 0.34 hours the amount has
changed from 42.5 g to 37.5 g? Give the halflife in minutes.
t = 0.34 hrs = 20.4 min
A = 37.5 g
A0 =42.5 g
ln [A/A0] = -kt
ln [37.5g / 42.5 g] = -k (20.4 min)
k = 0.00614 min-1
t1/2 = .693/k
t1/2 = .693/ 0.00614 min-1
t1/2 =110 min
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