Question

Uranium–232 has a half-life of 68.9 years. A sample from 206.7 years ago contains 1.40 g of uranium–232. How much uranium was originally present?

Answer 1

11.2 is the answer, the guy above just copied it from a guy on another question I think. And they are both wrong. 11.3 is not the answer.

Answer 2

Original amount of uranium is 11.3 g.

Step-by-step explanation:

Given data:

Half life of uranium = 68.9 years

Time taken in decaying= 206.7 years

Amount left after decaying = 1.40 g

Original amount of uranium = ?

Solution;

Formula:

K = 2.303/t log[A₀]/[A] ..... (1)

A₀ = initial amount

A = amount left after decaying

Value of K from first order kinetics.

Half life of uranium = 0.693 /K

68.9 years = 0.693 /k

k = 0.693/68.9 years

k = 0.0101 year⁻¹

Now we will put the values in formula (1)

K = 2.303/t log[A₀]/[A]

0.0101 year⁻¹ = 2.303/206.7 year log [A₀]/[1.40 g]

[A₀] = 11.3g

Original amount of uranium is 11.3 g.