Question

Bromine-82 has a half-life of about 35 hours.

After 140 hours, how many milliliters of an 80 mL sample will remain?

65 mL
20 mL
10 mL
5 mL

Answer 1

`\huge\boxed{\sf 5 \ mL}`

Explanation:

Amount of Br-82 = 80 mL

Half-life = 35 hours

Total time = 140 hours

No. of half lives spent:

= Total time / Half-life

= 140 / 35

= 4 half lives

After 1st half life:

= 80 / 2

= 40 mL

After 2nd half life:

= 40 / 2

= 20 mL

After 3rd half life:

= 20 / 2

= 10 mL

After 4th half life:

= 10 / 2

= 5 mL

`\rule[225]{225}{2}`