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Chemical Kinetics and Nuclear Chemistry question

2024 · 1 Feb · Shift 1 · Q30
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Chemical Kinetics and Nuclear Chemistry question

2024 · 1 Feb · Shift 1 · Q30

JEE MainChemistryChemical Kinetics and Nuclear ChemistryNumerical+4 / −1
The ratio of 14C12C\frac{{ }^{14} \mathrm{C}}{{ }^{12} \mathrm{C}}12C14C​ in a piece of wood is 18\frac{1}{8}81​ part that of atmosphere. If half life of 14C{ }^{14} \mathrm{C}14C is 5730 years, the age of wood sample is ‾\underline{\hspace{2cm}}​ years.
Numerical answer
View written solutionFree

Correct answer: 17190

  1. Let the initial ratio of 14C12C\dfrac{^{14}\mathrm{C}}{^{12}\mathrm{C}}12C14C​ in the living wood be the same as that in the atmosphere.

  2. After the wood is cut, 14C^{14}\mathrm{C}14C starts decaying while 12C^{12}\mathrm{C}12C remains unchanged. Hence, the ratio 14C12C\dfrac{^{14}\mathrm{C}}{^{12}\mathrm{C}}12C14C​ decreases exactly like the amount of 14C^{14}\mathrm{C}14C.

  3. Given: (14C12C)wood(14C12C)atmosphere=18\frac{\left(\dfrac{^{14}\mathrm{C}}{^{12}\mathrm{C}}\right)_{\text{wood}}}{\left(\dfrac{^{14}\mathrm{C}}{^{12}\mathrm{C}}\right)_{\text{atmosphere}}} = \frac{1}{8}(12C14C​)atmosphere​(12C14C​)wood​​=81​ So, the amount of 14C^{14}\mathrm{C}14C left is: NN0=18\frac{N}{N_0} = \frac{1}{8}N0​N​=81​

  4. Radioactive decay formula: N=N0(12)t/T1/2N = N_0\left(\frac{1}{2}\right)^{t/T_{1/2}}N=N0​(21​)t/T1/2​ where T1/2=5730T_{1/2} = 5730T1/2​=5730 years.

  5. Substitute the given ratio: 18=(12)t/5730\frac{1}{8} = \left(\frac{1}{2}\right)^{t/5730}81​=(21​)t/5730

  6. Since 18=(12)3\frac{1}{8} = \left(\frac{1}{2}\right)^381​=(21​)3 we get: (12)t/5730=(12)3\left(\frac{1}{2}\right)^{t/5730} = \left(\frac{1}{2}\right)^3(21​)t/5730=(21​)3

  7. Equating powers: t5730=3\frac{t}{5730} = 35730t​=3 t=3×5730=17190t = 3 \times 5730 = 17190t=3×5730=17190

  8. Therefore, the age of the wood sample is: 17190 years\boxed{17190\text{ years}}17190 years​

Comparison with stored correct answer:

  • Stored correct answer = 171901719017190
  • Derived answer = 171901719017190
  • They match.
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