Question

A rock is found to contain 2.2 grams of uranium-235, a radioactive isotope. If the rock has undergone 2.75 half-lives, what was the original amount of uranium-235 in the rock and how old is the rock

Answer 1

Answer:

=14.8 grams

Explanation:

The remaining amount is normally calculated using the formula:

Remaining mass= 1/2ⁿ × Original mass where n is the number of half-lives.

Therefore, original mass= Remaining mass × 2ⁿ

Remaining mass= 2.2 grams

Number of half lives= 2.75 half lives

Original mass= 2.2g × 2²·⁷⁵

=14.8 grams