IISER Chemistry - Nuclear Chemistry
Exam Duration: 45 Mins Total Questions : 30
Initial mass of a radioactive element is 16 gm. How many grams of it would be left after 24 years if its half life is 8 years?
- (a)
8
- (b)
4
- (c)
2
- (d)
1
For a first order, \({ C }_{ n }=\frac { 1 }{ { 2 }^{ n } } \times { C }_{ 0 }\) , where C0 where C0 and Cn are the initial and final concentration of the radioactive substance and n represents the number of half-life period elapsed.\({ C }_{ n }=\frac { 1 }{ { 2 }^{ n } } \times 16=2\)
Which of the following is radioactive?
- (a)
Li
- (b)
Rb
- (c)
Cs
- (d)
Fr
Outof four alkali metals francium is only radioactive
A photon of hard gamma-rays knocks a proton of 26Mg nuclues. The substance produced is
- (a)
an isotope nucleus 25Na
- (b)
an isobar nucleus 23Na
- (c)
an isotope nucleus 26Na
- (d)
an isobar nucleus 26Mg
\(_{ 12 }^{ 26 }{ Mg }+\Upsilon \rightarrow _{ 11 }^{ 25 }{ Na }+_{ l }^{ l }{ H }\)
The isotope 40K transforms into the isotope 40Ca. What kind of radioactive decay occurs in this case?
- (a)
k-electron capture
- (b)
\(\alpha-decay\)
- (c)
\(\beta-decay\)
- (d)
positron decay
\(_{ 19 }^{ 40 }{ K }\overset { -\beta }{ \longrightarrow } \quad _{ 20 }^{ 40 }{ Ca }\)
initial mass of a radioactive element is 160 g. How many grams of it would be left after 24 years if its half-life period is 6 years?
- (a)
6
- (b)
8
- (c)
10
- (d)
40
\({ C }_{ n }=\frac { 1 }{ { 2 }^{ 4 } } \times 160=10g\)
The fundamental particle responsible for keeping the nucleus together is
- (a)
meson
- (b)
antiproton
- (c)
positron
- (d)
hyperon
According to Yukawa, forces between nucleons result from an exchange of matter (mesons \(\pi \) ) or energy (photons) or both. Exchange forces are represented between unlike nucleons as
\(p\rightleftharpoons { \pi }^{ + }+n;n\rightleftharpoons { n }^{ - }+p\) or between like particles as:
\(p\rightleftharpoons { \pi }^{ o }+p;n\rightleftharpoons { \pi }^{ o }+n\)
The isotopic mass of \(_{ 92 }^{ 238 }{ U }\) is 238. 15 amu. its packing fraction is
- (a)
1.25
- (b)
0.125
- (c)
5.25
- (d)
9.5
Packing fraction = \(\frac { actual\quad isotopic\quad mass-mass\quad number\quad \times { 10 }^{ 4 } }{ mass\quad number } \)
= \(=\frac { 238.125\times 238 }{ 238 } \times { 10 }^{ 4 }=5.25\)
A device used for the measurement of radioactivity is
- (a)
mass spectrometer
- (b)
cyclotron
- (c)
nuclear reactor
- (d)
G.M. Counter
(a) is used to determine e/m ratio.
(b)Cyclotron and synchrotron are particle accelerators (25,000 miles per second)
(c)for counting the number of particles emitted per unit time Scintillation counter Wilson Cloud Chamber is also used for the same purpose.
Isobars are produced as a result of emission of
- (a)
\(\alpha\)-particle
- (b)
\(\beta\) -particle
- (c)
X-rays
- (d)
\(\gamma\)-rays
The radio isotope used in the treatment of cancer:
- (a)
C-12
- (b)
Co-60
- (c)
I-131
- (d)
P-32
(a) comprising atomic mass
(c) 1-131 hyperthyroidism.
(d) Leukemia, also used for temperature control in blood disease
Which of the following particles cannot be accelersted?
- (a)
\(\alpha\) -particles
- (b)
electrons
- (c)
neutrons
- (d)
protons
Neutrons being neutral cannot be accelerated
The artificial transmutation of elements was discovered by
- (a)
Bohr
- (b)
Rutherford
- (c)
J.J. Thomson
- (d)
Madam Curie
By Rutherford in 1915:
For(4n+2)series known as Uranium series the end product is \(_{ 82 }^{ 206 }{ Pb }\)
For (4n) series known as Thorium series, the end product is \(_{ 82 }^{ 206 }{ Pb }\)
For (4n+l) series known as series, the end product is product is \(_{ 83 }^{ 209 }{ Bi }\)
For (4n+3) series known as actinium series, the end product is \(_{ 82 }^{ 207 }{ Pb }\)
The half-time of a radioactive element depends on
- (a)
amount of element
- (b)
pressure
- (c)
temperature
- (d)
NONE OF THE ABOVE
Which of the radioactive isotopes is used for temperature control in blood disease?
- (a)
P-32
- (b)
H-3
- (c)
Rn-223
- (d)
I-131
An isotope is formed when successive radioactive emissions of an elements are
- (a)
\(\alpha, \alpha, \alpha\)
- (b)
\(\alpha, \beta, \alpha\)
- (c)
\(\alpha, \beta, \beta\)
- (d)
\(\beta, \beta, \beta\)
The half-life of \(_{ 84 }^{ 216 }{ Po }\) is 0.16 sec. How long will it take a sample of this nucleus to decay to 90 %
- (a)
0.16 sec
- (b)
0.32 sec
- (c)
0.48 sec
- (d)
0.53 sec
\(\frac { 0.693 }{ 0.16s } =\frac { 2.303 }{ t } log\frac { 100 }{ 10 } \)
\(t=\frac { 2.303\times 0.16s }{ 0.693 } =0.53s\)
Number of neutrons in a parent nucleus X, which gives \(_{ 7 }^{ 14 }{ N }\) after two successive \(\beta \) - emissions would be
- (a)
6
- (b)
7
- (c)
8
- (d)
9
\(_{ 5 }^{ 14 }{ X }\overset { -\beta }{ \longrightarrow } \quad _{ 6 }^{ 14 }{ Y }\overset { -\beta }{ \longrightarrow } \quad _{ 7 }^{ 14 }{ N }\)
No.of neutrons=14-5=9
In a radioactive decay which one of the following moves dastest?
- (a)
\(\alpha \)-particle
- (b)
\(\beta\)-particle
- (c)
\(\gamma\)-particle
- (d)
positron
⋎-rays has the lightest mass amongst all species given. The one with lightest mass shall move the fastest.
A radioactive element has t1/2 of 60 minutes. The amount remaininig after 3 hours is
- (a)
17.5%
- (b)
12.5%
- (c)
25%
- (d)
50%
t1/2 =60 min ;Total time 3 hrs:
No.of half lives =\(\frac { 180 }{ 60 } =3\)
Now: Nt = N0 \(\left[ \frac { 1 }{ 2 } \right] ^{ n }\)
Given N0 =100
∴ Nt =100 \(\left( \frac { 1 }{ 2 } \right) ^{ 3 }\)
\(\frac { 100 }{ 8 } \) =12.5 %
After emission of one \(\alpha\)-particle followed by one \(\beta\)-particle from \(_{ 35 }^{ 238 }{ X }\) , the number of neutrons in the atom will be
- (a)
142
- (b)
146
- (c)
144
- (d)
143
\(_{ 92 }^{ 238 }{ X }\overset { -\alpha }{ \longrightarrow } \quad _{ 90 }^{ 234 }{ X }\overset { -\beta }{ \longrightarrow } \quad _{ 91 }^{ 234 }{ X }\)
No.of neutrons =234-91=143
If half-life of substance is 5 years, then the total amount of substance left after 15 years, when initial amount is 64 gram.
- (a)
16 g
- (b)
2 g
- (c)
32 g
- (d)
8 g
Nt = No \(\left( \frac { 1 }{ 2 } \right) ^{ n }\)
=64 X \(\left( \frac { 1 }{ 2 } \right) ^{ 3 }\)
=8 g.
Which of the following is incorrect?
- (a)
45SC + \(_{ 0 }^{ 1 }{ n }\) \(\rightarrow\) 45Cu + \(_{ 1 }^{ 0 }{ n }\)
- (b)
209Bi + 2H \(\rightarrow\) 210Po + \(_{ 0 }^{ 1 }{ n }\)
- (c)
7Li + 1H \(\rightarrow\) 7Be + \(_{ 0 }^{ 1 }{ n }\)
- (d)
75As + 4He \(\rightarrow\) 78Br + \(_{ 0 }^{ 1 }{ n }\)
This is incorrect
Which of the following will be called projectile in the nucleus reaction? 14N + 4He \(\rightarrow\) 17O + 1H
- (a)
14N
- (b)
4He
- (c)
17O
- (d)
1H
The bombarding particle, i.e., \(\alpha \)-particle
The activity of a sample is defined as the number of disintegrations per unit time. If \(\lambda \) represents the decay or disintegration constant, the activity of the sample is given by
- (a)
N/No
- (b)
\(\lambda\)N
- (c)
N/\(\lambda\)
- (d)
None of these
Number of disintegrations per unit time represents the rate of disintegration,\(\left( -\frac { dN }{ dt } \right) \) which is proportional to N.
∴ \(-\frac { dN }{ dt } \alpha N\quad or\quad -\frac { dN }{ dt } (Rate)=\lambda n\)
The end product of (4n+2) disintegration series is
- (a)
\(_{ 82 }^{ 204 }{ Pb }\)
- (b)
\(_{ 82 }^{ 208 }{ Pb }\)
- (c)
\(_{ 82 }^{ 209 }{ Pb }\)
- (d)
\(_{ 82 }^{ 206 }{ Pb }\)
In the radiaactive change\(_{ Z }^{ A }{ P }\) \(\rightarrow\) \(_{ Z+1 }^{ A }{ Q }\) \(\rightarrow\) \(_{ Z-1 }^{ A-4 }R\) \(\rightarrow\) \(_{ Z-1 }^{ A-4 }{ S }\)
- (a)
\(\alpha, \beta, \gamma\)
- (b)
\(\gamma, \alpha, \beta\)
- (c)
\(\beta, \gamma , \alpha\)
- (d)
\(\beta, \alpha, \gamma\)
\(_{ Z }^{ A }{ P }\rightarrow \quad _{ z+1 }^{ A }{ Q }\)
Atomic number increases by one so -particle emission
\(^{ A }{ Q }\rightarrow \quad _{ z-1 }^{ A+4 }{ R }\)
Atomic number decreases by two and mass number by 4.So -particle emission
\(_{ z-1 }^{ A-4 }{ R }\rightarrow _{ z-1 }^{ A-4 }{ S }\)
No change in atomic number or mass number;so, \(\gamma \)-particle emission.
In the nuclear reaction \(_{ 92 }^{ 238 }U\) \(\rightarrow\) \(_{ 82 }^{ 206 }Pb\) the number of \(\alpha\) and \(\beta\) particles emitted are
- (a)
7\(\alpha\), 5\(\beta\)
- (b)
6\(\alpha\), 4\(\beta\)
- (c)
4\(\alpha\), 3\(\beta\)
- (d)
8\(\alpha\), 6\(\beta\)
4 α= Change in mass number
=238-206 =32
∴ α=8
2α -β = difference in atomic number
2 X 8-β = 10,β =6
Which one of the following notation shows the product incorrectly?
- (a)
\(_{ 96 }^{ 242 }{ CM(\alpha ,2n)_{ 97 }^{ 243 }{ Bk } }\)
- (b)
\(_{ 5 }^{ 10 }{ B(\alpha ,n)_{ 7 }^{ 13 }{ N } }\)
- (c)
\(_{ 7 }^{ 14 }{ N(n,p)_{ 6 }^{ 14 }{ C } }\)
- (d)
\(_{ 14 }^{ 28 }{ Si(d,n)_{ 15 }^{ 29 }{ P } }\)
In nuclear reactions the sum of atomic mass and number of reactants should be equal to atomic masses and atomic number of products. (Group displacement law).
1 mole of an \(\alpha \)-emiting nuclide \(_{ Z }^{ A }{ X }\) (half-time 10 hrs) was placed in sealed container .4.52 x 1023 helium atoms will accumlate in the container in
- (a)
4.552 hr
- (b)
9.40 hr
- (c)
10.00 hr
- (d)
20.00 hr
No. of moles of helium atoms formed
= \(\frac { 4.52\times { 10 }^{ 23 } }{ 6.02\times { 10 }^{ 23 } } =0.75\)
This means that if we start with I mole, then number of moles = 0.75 moles or 75% reaction is completed.Since t0.75 is double of T0.5
∴ time for accumulating Helium =2 X 10 =20 hrs
Which does not take place by \(\alpha \)-disintegration?
- (a)
\(_{ 92 }^{ 238 }{ U }\rightarrow _{ 90 }^{ 234 }{ U }\)
- (b)
\(_{ 90 }^{ 232 }{ Th }\rightarrow _{ 88 }^{ 228 }{ Ra }\)
- (c)
\(_{ 88 }^{ 226 }{ Ra }\rightarrow _{ 86 }^{ 223 }{ Rn}\)
- (d)
\(_{ 83 }^{ 213 }{ Bi }\rightarrow _{ 84 }^{ 213 }{ Po }\)
Only this occurs with a β-decay
1654060945.png)
1654060942.png)
1653987551.png)
1653987086.png)
1582095229.jpg)
