Problem 40 - A Complete Resource Book in Chemistry for JEE Main

Question

Carbon- 14 dating method is based on the fact that (a) C-14 fraction is same in all objects (b) C-14 is highly insoluble (c) ratio of carbon- 14 and carbon-12 is constant (d) all the above

Step-by-Step Solution

Answer

The correct option is (c) the ratio of carbon-14 and carbon-12 is constant.

Step 1: Understanding Carbon-14 Dating

Carbon-14 dating, also known as radiocarbon dating, is used to determine the age of carbonaceous materials up to about 60,000 years. It is based on the decay of carbon-14, a radioactive isotope of carbon.

Step 2: Examining the Options

Let's examine the given options to see which describes the principle of carbon-14 dating: a) C-14 fraction is same in all objects. b) C-14 is highly insoluble. c) Ratio of C-14 and C-12 is constant. d) All the above.

Step 3: Analyzing Option A

The statement that "C-14 fraction is same in all objects" is not correct. The fraction of C-14 varies as it depends on the life cycle and the environment of the organism.

Step 4: Analyzing Option B

The statement that "C-14 is highly insoluble" is irrelevant to the process of carbon-14 dating. Solubility has no significant effect on the decay used for dating.

Step 5: Analyzing Option C

The principle behind carbon-14 dating indeed involves the ratio of carbon-14 to carbon-12 being constant at the time of the organism's death. Living organisms maintain a constant ratio of C-14 and C-12 by exchanging carbon with their surroundings until they die, after which C-14 decays while C-12 remains constant. This change in ratio is used to date the age.

Step 6: Determining the Correct Answer

Based on our analysis, option c is the correct statement. It is the basis on which the carbon-14 dating method operates.

Key Concepts

Radiocarbon Dating

Radiocarbon dating is an essential tool for archaeologists and scientists in determining the age of ancient objects. This method is also known as carbon-14 dating, as it relies on measuring the decay of carbon-14, a radioactive isotope of carbon. When living organisms are alive, they absorb carbon dioxide, which includes a mix of carbon-12 and carbon-14 isotopes, in a ratio common to the atmosphere. Once the organism dies, it stops absorbing carbon, and the carbon-14 it contains slowly decays over time. By measuring the remaining amount of carbon-14 and comparing it to carbon-12, scientists can estimate how long it has been since the organism's death.

The technique is powerful because it allows us to date organic materials up to about 60,000 years old. It's widely used to date historical objects such as ancient artifacts, fossils, and geological samples. Since carbon-14 has a half-life of approximately 5,730 years, it is particularly useful for understanding human history and prehistoric life. However, for items significantly older than 60,000 years, other dating methods must be employed.

Radioactive Isotope

Radioactive isotopes are variants of chemical elements that have an unstable nucleus. The instability causes them to undergo radioactive decay, gradually transforming into other elements. Carbon-14 is a well-known radioactive isotope used in radiocarbon dating. The process of decay is consistent and occurs at a predictable rate, which is useful in dating historical items.

Here’s something interesting about radioactive isotopes:

• They decay over time, releasing particles and energy.
• This decay process can be used as a natural clock to date materials.
• The rate at which a radioactive isotope decays is expressed as its half-life, the time it takes for half of a sample of the isotope to decay.

For carbon-14, its half-life is around 5,730 years. This property makes radioactive isotopes particularly valuable to scientists, enabling them to track historical timelines accurately. Radioactive isotopes are not only useful in dating but also have diverse applications in medicine and energy.

Carbon-12

Carbon-12 is one of the stable isotopes of carbon and is non-radioactive. In the context of radiocarbon dating, it serves as a comparison standard for carbon-14. Living organisms maintain a consistent ratio of carbon-14 to carbon-12 in their bodies while they are alive. Once they die, the carbon-14 begins to decay, and the ratio changes, which is crucial for dating.

It’s important to note that:

• Carbon-12 makes up the majority of carbon found in nature, hence it's stable and non-decaying.
• The constant ratio of carbon-12 to carbon in the atmosphere allows a baseline for comparing the decay progress of carbon-14.
• This comparison enables scientists to calculate the time elapsed since the organism's death.

The stability of carbon-12 reinforces the reliability of radiocarbon dating, as it provides a steady measure against which carbon-14’s decay is tracked. Understanding the interaction between these isotopes helps give a clearer picture of their role in scientific dating techniques.