St Peter the Apostle High School
Nuclear Chemistry
N5 Homework Questions
Answer questions as directed by
your teacher.
Chemistry Department
National 5 Questions
Radiation
1. Alpha, beta and gamma radiation have different penetrating properties. Name the
type of radiation which is:
(a) able to penetrate 5cm lead
(b) stopped by a sheet of paper
(c) stopped by a sheet of aluminium.
(3)
2.
(1)
Nuclear Equations
1. Uranium 238 decays by alpha-emission to form isotope X. Isotope X then decays,
emitting Y to form protactinium 234. Identify X and Y.
2. What is formed when an atom of
A
3.
240
91
Pa
B
239
91
239
92
(2)
U emits a beta particle?
Pa
C
239
93
Np
D
238
U
92
(1)
Protactinium 231 is formed by beta emission from a radioisotope of thorium.
What is the mass number of the radioisotope of thorium?
A 230
4.
B 231
C 232
D 235
(1)
What is formed when radium 224 emits an alpha particle?
A radon 220 B radon 222
5.
C actinium 224
D thorium 228
(1)
Copy and complete the following equations:
6.
(a)
234
90
Th
+
0e
-1
(1)
(b)
222
86
Rn
+
4
2
(1)
He
Find X, Y and Z in:
(a)
(b)
(c)
6 Li
3
234
U
92
+
1
0
3
1
n
Y
+
212
Bi
83
Z
+
H
4
He
2
0
-1
+
X
(1)
(1)
e
(1)
Half Life
1.
24
Na is a beta emitter with a half life of 15 hours. What percentage of the original
isotope would remain after 45 hours?
A 12.5
B 25
C 75
D 87.5
(1)
2.
14
C has a half life of 5600 years. An analysis of charcoal from a wood fire shows
that its 14 C content is 25% that of living wood. How many years have passed since
the wood for the fire was cut?
A 1400
3.
5.
6.
7.
8.
C 11200
D 16800
(1)
After 48 years the level of radioactivity in a sample of an isotope was found to be
1/8th of the level originally. What is the half life of the isotope?
A 6 years
4.
B 4200
The half-life of
84 years.
B 12 years C 16 years D 24 years
210
(1)
Pb is 21 years. Calculate the mass left of a 40g sample after
Calculate the half-life of
(2)
220
Rn if it takes 220s to decrease its radioactivity to 1/16.
(2)
24
Na has a half life of 15 hours. What fraction of a sample’s activity will remain
after 5 days.
(2)
A luminous watch dial containing 147 Pm (t1/2 = 2.5 years) has only 1/8 of its
original ‘glow’. How old is the watch?
(2)
The radioisotope 131I is used in hospitals. It has a half-life of 8 days and decays to
give a stable product. A bag of hospital linen contaminated with 131 I was found to
give a count rate of 320 counts s-1.
(a) Draw a graph to show how the count rate of the linen will change with time.
(b) Hospitals are not allowed to dispose of material contaminated with I 131
until the count rate has fallen to 30 counts s-1. Use the graph to determine
how long the bag of linen must be stored before disposal.
(3)
(1)
Radioisotopes
1.
2.
The isotope 60Co has a half life of 5.3 years and is used to supply gamma radiation
from outside the body of a patient. Give two reasons why this isotope would not be
suitable for use inside the body.
(2)
Radioisotopes are used in a wide variety of ways.
(a) Name a radioisotope used in medicine and give its use.
(b) Describe an industrial use for a radioisotope.
(2)
Miscellaneous
1.
14C
is a radioactive isotope of carbon. It is produced in the upper atmosphere
when 14N atoms are bombarded by neutrons from space. If a neutron is captured
by a 14N nucleus, a 14C isotope is produced along with one other particle.
(a)
Copy and complete the nuclear equation for the formation of carbon-14.
(b)
14C
(c)
decays by beta emission. Why does the atomic number increase by
one unit when a 14C nucleus decays?
(1)
(1)
Carbon dating can be used to estimate the age of wood found in archaeological
sites. The decay curve shows the decrease in the percentage of 14C against the
number of half-lives.
(i) A piece of wood was found to contain 5% of the original 14C content. The half
life of 14C is 5700 years. Calculate the age of the wood in years.
(ii) Suggest a reason why 14C is unsuitable for dating samples that are more than
50,000 years old.
(1)
(1)
2. The age of a rock found in Canada was determined by measuring the amounts of
argon-40 and potassium-40 present in a sample.
(a) Each potassium-40 atom can emit a single positron particle to form an argon-40
atom. Work out the mass number and atomic number for a positron.
(b) 75% of the potassium-40 atoms originally present in the rock sample were found
to have undergone radioactive decay. The half-life of potassium-40 is
1.26 x 109 years. Calculate the age of the rock in years.
(1)
(1)
3. Phosphorous-32 and strontium-89 are two radioisotopes used to study how far
mosquitoes travel.
(a) Strontium-89 decays by emission of a beta particle. Copy and complete the
nuclear equation for the decay of strontium-89.
89Sr
(b)
(c)
In an experiment, 10g of strontium-89 chloride was added to a sugar solution used
to feed mosquitoes.
(i) The strontium-89 chloride solution was fed to the mosquitoes in a laboratory at
20oC. When the mosquitoes were released the outdoor temperature was 35oC.
What effect would the increase in temperature have on the half-life of the
strontium-89?
(ii) Calculate the mass, in grams, of strontium-89 present in the 10g sample
of strontium-89 chloride, SrCl2.
A mosquito fed on a solution containing phosphorous-32 is released. Phosphorous
-32 has a half-life of 14 days. When the mosquito is recaptured 28 days later, what
fraction of the phosphorous-32 will remain?
(1)
(1)
(1)
4. Positron emission tomography, PET, is a technique that provides information about
biochemical processes in the body. Carbon-11, 11C, is a positron-emitting radioisotope
that is injected into the bloodstream. A positron can be represented as 0 e.
1
(a)
Complete the nuclear equation for the decay of
11C
by positron emission.
11C
(b)
(c)
A sample of 11C had an initial count rate of 640 counts min-1. After 1 hour the
count rate had fallen to 80 counts min-1. Calculate the half-life, in minutes, of 11C.
(1)
(1)
11C
is injected into the bloodstream as glucose molecules (C6H12O6). Some of the
carbon atoms in these glucose molecules are 11C atoms. The intensity of radiation
in a sample of 11C is compared with the intensity of radiation in a sample of glucose
containing 11C atoms. Both samples have the same mass.
Which sample has the higher intensity of radiation? Give a reason for your answer.
(1)
5.
(1)