Name: __________________________,__________________
Nuclear Chemistry Worksheet # 2
1) Nuclei above the belt of stability can lower their neutron-to-proton ratio by________.
A) beta emission.
B) gamma emission.
C) positron emission.
D) electron capture.
E) Any of the above processes will lower the neutron-to-proton ratio.
2) What is the largest number of protons that can exist in a nucleus and still be stable __________?
A) 206
B) 50
C) 92
D) 83
E) 84
3) The largest number of stable nuclei have an __________ number of protons and an __________ number of
neutrons.
A) even, even
B) odd, odd
C) even, odd
D) odd, even
E) even, equal
4) At approximately what number of protons, or neutrons, does the 1:1 ratio of protons to neutrons start to produce
unstable nuclei?
A) 10
B) 20
C) 30
D) 50
E) 80
5) Which of these nuclides is most likely to be radioactive?
127
243
39
27
A)
K
B)
Al
C)
I
D)
Am
53
95
19
13
E)
209
Bi
83
Free Response:
1)
240 grams of a sample of radium-226 has a half-life of 1600 years. How many grams
of radium-226 will remain after 6400 years?
2)
A 200-mg sample of an unknown radioisotope decays to 25-mg in 60 minutes. What
is the half-life of the isotope?
3)
What is the number of half-life periods required for a sample of a radioactive material
to decay to one-sixteenth of its original mass?
4)
A sample of iodine-131 emits 48: Ci of radiation on May 2nd. How many : Ci of
radiation will the sample emit on May 26th?
5)
A 40.0 mg sample of phosphorus-33 decays to 10.0 mg in 50.0 days. What is the
half-life of phosphorus-33?
6)
After 112 years, only 2.0 grams of a sample of strontium-90 remains unchanged.
What was the mass of strontium-90 in the original sample?
7)
After 75.0 hours, 5.0 mg of a sample of a substance with a half-life of 15.0 hours
remains in a container. What was the mass of the sample in the container when the
experiment began?
8)
25-mg of francium-220 (Fr) has a count rate of 960 counts per minute at 2:00:00 pm.
What will be the count rate at 2:02:45 pm?
9)
A student performed an experiment designed to determine the half-life of copper-59.
At 11:05 am on a certain day, he measured the activity of a sample of copper-59 to be
3584 counts per minute. By 11:55 am the same day, the count rate had dropped to
112 counts per minute. What is the half-life of copper-59?
10)
10:00 am this morning, a scientist measured the activity of a sample of potassium-42
to be 460 disintegrations per second (dps). What must have been the activity at 9:12
am yesterday morning?
11)
A sample of iodine-131 contains 2000 atoms of iodine-131. How many atoms of
radioactive iodine would remain after 30 days? The half-life of iodine-131 is 8.07
days.
12)
What fraction of a sample of radioactive atoms would remain in the sample after 2.49
months if the nuclide has a half-life of 6.00 months?
13)
How long will to take a sample of radium-226 to decay to 40.0% of its original
amount? t1/2 = 1600 years.
14)
When 85 grams of a radioisotope is allowed to decay naturally for 20. days, 74 grams
remain. Calculate the half-life of this nuclide.
15)
A tissue sample from a certain mummified body was found to contain 2232 atoms of
carbon-14. A similar live tissue sample was found to contain 2400. Atoms of carbon14. If the half-life of carbon-14 is 5730 years, how old in the mummy?
16)
How many grams of phosphorus-32 would remain in a sample containing 250. mg
after it has been allowed to decay for 50.0 days? (t½ = 14.3 days)
AP Chemistry
1989 D
The carbon isotope of mass 12 is stable. The carbon isotopes of mass 11 and mass 14 are unstable.
However, the type of radioactivity decay is different for these two isotopes. Carbon-12 is not produced in
either case.
(a) Identify a type of decay expected for carbon-11 and write the balanced nuclear reaction
for that decay process.
(b) Identify the type of decay expected for carbon-14 and write the balanced nuclear reaction
for that decay process.
(c) Gamma rays are observed during the radioactive decay of carbon-11. Why is it
unnecessary to include the gamma rays in the radioactive decay equation of (a)?
(d) Explain how the amount of carbon-14 in a piece of wood can be used to determine when the
tree died.