Question

A sample initially contains 8.0 moles of a radioactive isotope. How much of the sample remains after four half-lives? Express your answer using two significant figures.

Answer 1

0.50 mol

Step-by-step explanation:

The half-life is the time required for the amount of a radioactive isotope to decay to half that amount.

Initially, there are 8.0 moles.

• After 1 half-life, there remain 1/2 × 8.0 mol = 4.0 mol.

• After 2 half-lives, there remain 1/2 × 4.0 mol = 2.0 mol.

• After 3 half-lives, there remain 1/2 × 2.0 mol = 1.0 mol.

• After 4 half-lives, there remain 1/2 × 1.0 mol = 0.50 mol.