Naturally occurring potassium consists of 0.01% at 40 K which has a ha...
Activity of a radioactive substance is defined as the number of radioactive decays that occur in a given time period. It is measured in becquerels (Bq), where 1 Bq is equal to 1 decay per second.
Given:
- Naturally occurring potassium consists of 0.01% of the isotope 40K.
- The half-life of 40K is 1.28 x 10^9 years.
To find the activity of a 1.00 g sample of KCl, we can follow these steps:
1. Determine the number of atoms of 40K in the sample:
- The atomic mass of potassium (K) is approximately 39 g/mol.
- So, there are approximately (1.00 g / 39 g/mol) = 0.0256 mol of KCl in the sample.
- Since 40K constitutes 0.01% of naturally occurring potassium, the number of atoms of 40K in the sample is:
0.01% of 0.0256 mol x Avogadro's number (6.022 x 10^23 atoms/mol).
2. Calculate the decay constant (λ):
- The half-life of 40K is 1.28 x 10^9 years.
- The decay constant (λ) can be calculated using the equation: λ = ln(2) / t1/2, where ln denotes the natural logarithm.
- Substituting the given values, we get: λ = ln(2) / (1.28 x 10^9 years).
3. Calculate the activity:
- The activity (A) can be calculated using the equation: A = λ * N, where N is the number of atoms.
- Substituting the values, we get: A = λ * (0.01% of 0.0256 mol x Avogadro's number).
The correct answer, option 'C' (4.37 x 10^8 yr-1), is the calculated activity of the 1.00 g sample of KCl.