Test Index

NCERT Class XII Chemistry
Chapter - Chemical Kinetics
Questions with Solutions

© examsnet.com
Question : 17
Total: 39
During nuclear explosion, one of the products is ‌90Sr with half-life of 28.1 years. If 1 µg of ‌90Sr was absorbed in the bones of a newly born baby instead of calcium, how much of it will remain after 10 years and 60 years if it is not lost metabolically ?
Solution:  
As radioactive disintegration follows first order kinetics. Hence Decay constant of 90 ‌Sr,(λ)=
0.693
t1∕2
=
0.693
28.1
 =2.466×10−2 yr−1
To calculate the amount left after 10 years
Given, [R0]=1µg,
t=10 years,
k=2.466×10−2 yr−1,[R]=?
Using formula, λ=
2.303
t
‌log‌
[R0 ]
[R]
or 2.466×10−2= 2.30310‌log‌
1
[R]
or,
2.466×10−2×10
2.303
=−log[R]
or, log[R]=−0.1071
or, [R]= Antilog (−0.1071)=0.7814µg
To calculate the amount left after 60 years, t = 60 years, [R0] = 1 µg, [R] = ?
or, 2.466×10−2=
2.303
60
‌log‌
1
[R]
or,
2.466×10−2×60
2.303
=−log[R]
or,log[R]=−0.6425
or, [R]= Antilog (−0.6425)=0.2278µg
© examsnet.com
Go to Question:
Prev Question
Next Question