Question

An isotope has a half life of 5 minutes. How much of a 100 gram sample of this isotope is left after 20 minutes?

Answer 1

Answer:

6.25 gram

Explanation:

Applying,

R = R'($2^{a/n}$)................ Equation 1

Where R = Original mass of the isotope, R' = mass of the isotope left after disintegration, a = Total time, n = half life.

make R' the subject of the equation

R' = R/($2^{a/n}$)................. Equation 2

From the question,

Given: R = 100 gram, a = 20 munites, n = 5 minutes.

Substitute these values into equation 2

R' = 100/($2^{20/5}$)

R' = 100/$2^{4}$

R' = 100/16

R' = 6.25 gram