Question

Element X decays radioactively with a half life of 11 minutes. If there are 870 grams

of Element X, how long, to the nearest tenth of a minute, would it take the element to
decay to 154 grams?
y = a(.5) t/h​

Answer 1

27.5 minutes

Explanation:

Using,

R/R' = 2ᵃ/ᵇ------------------ Equation 1

From the equation,

R = mass of Element X before radioactive decay, R' = mass of element X after radioactive decay, a = Time taken, b = half life.

Given: R = 870 grams, R' = 154 grams, b = 11 minutes.

Substitute these values into equation 1

870/154 = 2ᵃ/¹¹

(870/154)¹¹ = 2ᵃ

Solve for a

2ᵃ = (5.649)¹¹

2ᵃ = 187061.26

Taking the logarithm of both side,

Log2ᵃ = Log(187061.26)

⇒ a = log(187061.26)/log2

a = 8.272/0.301

a = 27.5 minutes