A sample of wooden air craft is found to undergo 9 dpm \(g^{-1}\) of \(C^{14}\). What is approximate age of air craft? The half life of \(_{6} \mathrm{C}^{14}\) is 5730 year and rate of disintegration of wood recently cut down is 15 dpm \(\mathrm{g}^{-1}\) of \(_{6} \mathrm{C}^{14} ?\)

Short Answer

Expert verified
The approximate age of the wooden aircraft is 4224 years.

Step by step solution

01

Determine the Disintegration Rate

Identify the disintegration rates for both the wooden aircraft sample and the freshly cut wood. The aircraft sample has a disintegration rate of 9 dpm (disintegrations per minute) per gram, and freshly cut wood has a rate of 15 dpm per gram.
02

Calculate the Ratio of the Disintegration Rates

Calculate the ratio of the disintegration rate of the aircraft sample to the disintegration rate of fresh wood. This is done by dividing the disintegration rate of the aircraft sample by the disintegration rate of the fresh wood: \( \frac{9 \ dpm/g}{15 \ dpm/g} = 0.6 \).
03

Use the Radioactive Decay Formula

Use the formula for radioactive decay, which relates the remaining amount of a substance to its half-life. The formula is \( N(t) = N_0 \times \left(\frac{1}{2}\right)^{t/T} \) where \( N(t) \) is the remaining amount of substance at time \( t \) and \( N_0 \) is the initial amount. In this case, \( N(t) / N_0 = 0.6 \) and \( T \) is the half-life of \( C^{14} \) which is 5730 years.
04

Solve for the Age of the Air Craft

Plug the known values into the decay formula and solve for \( t \) (time elapsed or the age of the aircraft) by taking the logarithm of both sides: \( t = T \times \frac{\log(N(t)/N_0)}{\log(1/2)} \). Plugging in the values gives us: \( t = 5730 \times \frac{\log(0.6)}{\log(0.5)} \. \)
05

Calculate the Logarithm and the Age

Perform the calculations to find the age of the wooden aircraft: \( t = 5730 \times \frac{\log(0.6)}{\log(0.5)} \approx 5730 \times 0.737 \), which yields \( t \approx 4224 \) years.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Radioactive Decay
Radioactive decay is a fundamental process by which an unstable atomic nucleus loses energy by emitting radiation. In the context of carbon-14 (C14), it refers to the transformation of this radiocarbon isotope into a more stable nitrogen-14 (N14) nucleus over time. This process occurs at a predictable rate, characterized by the nuclide's half-life. When an organism dies, it stops absorbing C14, and the amount of C14 in its tissues begins to decrease through radioactive decay. By measuring the remaining C14, scientists can estimate the time since the organism's death, which is the principle behind carbon-14 dating.

Understanding radioactive decay enables us to estimate the age of ancient objects, such as the wooden aircraft in our problem. This natural clock provides invaluable time stamps for archaeological and geological materials, making it one of the most widely used tools in science for dating artifacts.
Half-Life Calculation
The half-life of a radioactive isotope is the time required for half of the radioactive atoms in a sample to decay. For carbon-14 (C14), this value is approximately 5730 years. A crucial aspect of half-life calculation is understanding that it is a constant value that does not depend on the size of the sample or its initial amount. Instead, it solely depends on the properties of the isotope itself.

In the calculation for the wooden aircraft's age, we use the half-life to determine how many years have passed for the disintegration rate to drop from 15 dpm/g to 9 dpm/g. Since half-life remains consistent, we can input it into calculations as a known variable to help solve for the age of our sample. This principle enables us to decode historical timelines, geologically date layers of earth, and even measure the decay in living systems.
Logarithmic Equations in Chemistry
Logarithmic equations are indispensable in chemistry, especially for analyzing processes that follow an exponential trend such as radioactive decay. The logarithm essentially allows us to solve for the power to which a number must be raised to get another number, which in the case of decay, helps to determine the time involved in the process.

Using logarithms, we can rearrange the decay formula to solve for the age of the wooden aircraft. By taking the natural log (ln) or log to base 10 of both sides of the decay equation, we isolate the variable representing time. This mathematical operation converts an exponential equation into a linear one that we can solve using algebra. In our exercise, it was necessary to employ a logarithmic equation to figure out how long the C14 had been decaying in the aircraft wood. This utilization of logarithms is a textbook example of applying mathematical concepts to solve practical problems in chemistry and beyond.

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Most popular questions from this chapter

A piece of wood from an archeological source shows a \({ }^{14} \mathrm{C}\) activity which is \(60 \%\) of the activity found in fresh wood today. Calculate the age of the archeological sample. \(\left(t_{1 / 2}{ }^{14} \mathrm{C}=5770\right.\) year \()\)

A \(0.2 \mathrm{~mL}\) sample of a solution containing \(1.0 \times 10^{-7}\) curie of \(_{1} \mathrm{H}^{3}\) is injected to the blood stream of an animal. After sufficient time for circulatory equilibrium to be established, \(0.10 \mathrm{~mL}\) of blood is found to have an activity of \(20 \mathrm{dpm}\). Calculate the volume of blood in animal, assuming no change in activity of sample during criculatory equilibrium.

The \(\beta^{-}\) -activity of a sample of \(\mathrm{CO}_{2}\) prepared from a contemporary wood gave a count rate of \(25.5\) counts per minute (c.p.m.). The same mass of \(\mathrm{CO}_{2}\) from an ancient wooden statue gave a count rate of \(20.5 \mathrm{cpm} .\), in the same counter condition. Calculate its age to the nearest 50 year taking \(t_{1 / 2}\) for \({ }^{14} \mathrm{C}\) as 5770 year. What would be the expected count rate of an identical mass of \(\mathrm{CO}_{2}\) from a sample which is 4000 year old?

Give one example each of (a) \(\alpha\) -emission, (b) \(\beta^{+}\) -emission, and (c) K-capture. Write the equation for these nuclear changes.

\begin{aligned} &\text { How many } \alpha-\text { and } \beta \text { -particles will be emitted when }{ }_{90} \mathrm{Th}^{232} \text { changes }\\\ &\text { into }{ }_{82} \mathrm{~Pb}^{208} \text { ? } \end{aligned}

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